Systematics, biodiversity, and paleoecology of an early Danian decapod crustacean assemblage from Alabama, United States

2025  47  13 geodiversitas Geodiversitas est une revue en flux continu publiée par les Publications scientifiques du Muséum, Paris Geodiversitas is a fast track journal published by the Museum Science Press, Paris Les Publications scientifiques du Muséum publient aussi / The Museum Science Press also publish: Adansonia, Zoosystema, Anthropozoologica, European Journal of Taxonomy, Naturae, Cryptogamie sous-sections Algologie, Bryologie, Mycologie, Comptes Rendus Palevol Diffusion – Publications scientifiques Muséum national d’Histoire naturelle CP 41 – 57 rue Cuvier F-75231 Paris cedex 05 (France) Tél. : 33 (0)1 40 79 48 05 / Fax : 33 (0)1 40 79 38 40 [email protected] / http://sciencepress.mnhn.fr © Publications scientifiques du Muséum national d’Histoire naturelle, Paris, 2025 ISSN (imprimé / print) : 1280-9659/ ISSN (électronique / electronic) : 1638-9395 Directeur De la publication / Publication director : Gilles Bloch, Président du Muséum national d’Histoire naturelle réDacteur en chef / editor-in-chief : Didier Merle assistant De réDaction / assistant editor : Emmanuel Côtez ([email protected]) Mise en page / Page layout : Audrina Neveu, Pénélope Laurin coMité scientifique / scientific board : Christine Argot (Muséum national d’Histoire naturelle, Paris) Beatrix Azanza (Museo Nacional de Ciencias Naturales, Madrid) Raymond L. 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Geodiversitas est indexé dans / Geodiversitas is indexed in: – Science Citation Index Expanded (SciSearch®) – ISI Alerting Services® – Current Contents® / Physical, Chemical, and Earth Sciences® – Scopus® Geodiversitas est distribué en version électronique par / Geodiversitas is distributed electronically by: – BioOne® (http://www.bioone.org) Les articles ainsi que les nouveautés nomenclaturales publiés dans Geodiversitas sont référencés par / Articles and nomenclatural novelties published in Geodiversitas are referenced by: – ZooBank® (http://zoobank.org) 577 GEODIVERSITAS • 2025 • 47 (13) © Publications scientifiques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com Systematics, biodiversity, and paleoecology of an early Danian decapod crustacean assemblage from Alabama, United States Adiël A. KLOMPMAKER P. George MARTIN Department of Museum Research and Collections & Alabama Museum of Natural History, University of Alabama, 500 Hackberry Lane, Tuscaloosa, Alabama 35487 (United States) [email protected] (corresponding author) [email protected] Matúš HYŽNÝ Earth Science Institute, Slovak Academy of Sciences, Dúbravská cesta 9, SK-840 05 Bratislava (Slovakia) and Department of Geology and Paleontology, Faculty of Natural Sciences, Comenius University, Ilkovičova 6, SK-842 15 Bratislava (Slovakia) [email protected] Andrew R. BOWMAN Geological Survey of Alabama, P.O. Box 869999, 420 Hackberry Lane, Tuscaloosa, Alabama 35486 (United States) [email protected] George E. PHILLIPS Mississippi Museum of Natural Science, 2148 Riverside Dr, Jackson, Mississippi 39202 (United States) [email protected] Roger W. PORTELL Florida Museum of Natural History, University of Florida, 1659 Museum Road, Gainesville, Florida 32611 (United States) [email protected] Submitted on 20 September 2024 | accepted on 22 December 2024 | published on 22 September 2025 urn:lsid:zoobank.org:pub:F5144147-C045-48FD-8128-7F822CDE6B18 Klompmaker A. A., Martin P. G., Hyžný M., Bowman A. R., Phillips G. E. & Portell R. W. 2025. — Systematics, biodiversity, and paleoecology of an early Danian decapod crustacean assemblage from Alabama, United States. Geodiversitas 47 (13): 577-622. https://doi.org/10.5252/geodiversitas2024v47a13. http://geodiversitas.com/47/13 ABSTRACT The extent to which the Cretaceous-Paleogene (K-Pg) extinction event impacted decapod crustaceans has yet to be tested rigorously due to a lack of studies at the outcrop scale. We comprehensively describe an early but not earliest Danian assemblage from Mussel Creek, central Alabama, United States, based on collecting of decapod carapaces and appendage remains at the roadcut part of this site since 2010. The specimens were recovered chiefly from silty, micaceous mudstones of the Pine Barren Member 578 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. INTRODUCTION The degree to which decapod crustaceans experienced extinction during the Cretaceous-Paleogene mass extinction event remains an open question as analyses have been done largely at a global scale and at different taxonomic levels (e.g., Schweitzer & Feldmann 2005, 2023; Klompmaker etal. 2016). Early Paleocene (Danian) decapod crustaceans provide insights into their biodiversity after this extinction event. Such assemblages have been described from multiple continents including Antarctica (Feldmann & Tshudy 1989), Europe (Jakobsen & Collins 1997; Robin etal. 2017), North America (Rathbun 1935a; Collins & Wienberg Rasmussen 1992; Armstrong etal. 2009), and South America (Feldmann etal. 1995). The stratigraphic position of these assemblages within the Danian is critical to evaluate the biodiversity of decapods after the mass extinction. The Clayton Formation is a lower Danian unit exposed in the southeastern United States known to yield decapods. Decapods or their burrows have been reported from the Clayton Formation from Illinois (Cope etal. 2005), Arkansas (Rathbun 1935a; Martínez-Díaz etal. 2016), and Alabama (Feldmann etal. 2014, 2019; Martínez-Díaz etal. 2016; Foster etal. 2020), but these papers focused on selected taxa for the purposes of their studies or reported on a limited number of specimens. The goal of this paper is to comprehensively describe an early Paleocene (early Danian) decapod assemblage from the Pine Barren Member of the Clayton Formation in central Alabama, United States. Based on collecting efforts spanning 15 years, we clarify the taxonomy of some previously reported taxa; report multiple new records and taxa; and discuss the stratigraphic and paleobiogeographic implications, paleoecology, and diversity of this assemblage. within the Clayton Formation, c. 8 m above the K-Pg boundary. Microfossil analysis indicates that the decapods originate from the lower middle part of the NP2 nannofossil zone, c. 600-700 ka after the K-Pg boundary. Based on 354 identifiable specimens, we recognize eight species: 1) four Brachyura: Alahexapus martini (Feldmann, Schweitzer & Portell, 2014) n. comb., Costacopluma nicksabani n. sp., Raninoides danicus n. sp., and an indeterminate representative of Palaeoxanthopsidae Schweitzer, 2003; 2) three Axiidea: Alphacheles zeta (Rathbun, 1936) n. comb., Ctenocheles sp., and Eucalliaxiopsis alabamensis (Rathbun, 1935a) n. comb.; and 3) one Paguroidea: “Paguristes” johnsoni Rathbun, 1935a. Two new genera are described: Alahexapus n. gen. and Alphacheles n. gen. The assemblage is dominated by specimens of C. nicksabani n. sp. (52% of identifiable specimens) and E.alabamensis n. comb. (31%). Three specimens of C. nicksabani n. sp. preserve rare gonopods. A rarefaction analysis indicates that (nearly) all species were collected. This assemblage represents the most diverse early Danian decapod assemblage from North America thus far, and provides a basis for further study of decapods across the K-Pg boundary. RÉSUMÉ Systématique, biodiversité et paléoécologie d’un assemblage de crustacés décapodes du Danien inférieur de l’Alabama, États-Unis. L’ampleur de l’impact de l’extinction du Crétacé-Paléogène (K-Pg) sur les crustacés décapodes n’a pas encore été rigoureusement évaluée en raison du manque d’études à l’échelle des affleurements. Nous décrivons de manière exhaustive un assemblage du Danien inférieur, mais pas le plus ancien, provenant de Mussel Creek, dans le centre de l’Alabama, aux États-Unis, sur la base de la collecte collecte de restes de carapaces et d’appendices de décapodes dans un talus routier depuis 2010. Les spécimens ont été principalement collectés dans des mudstones limoneux et micacés du Membre Pine Barren au sein de la Formation Clayton, à environ 8 m au-dessus de la limite K-Pg. L’analyse des microfossiles indique que les décapodes proviennent de la partie inférieure moyenne de la zone à nannofossiles NP2, environ 600 à 700 ka après la limite K-Pg. Sur la base de 354 spécimens identifiables, nous reconnaissons huit espèces : 1) quatre Brachyura : Alahexapus martini (Feldmann, Schweitzer & Portell, 2014) n. comb., Costacopluma nicksabani n. sp., Raninoides danicus n. sp. et un représentant indéterminé de la famille des Palaeoxanthopsidae Schweitzer, 2003 ; 2) trois Axiidea : Alphacheles zeta (Rathbun, 1936) n. comb., Ctenocheles sp. et Eucalliaxiopsis alabamensis (Rathbun, 1935a) n. comb. ; et 3) un Paguroidea : “Paguristes” johnsoni Rathbun, 1935a. Deux nouveaux genres sont décrits : Alahexapus n. gen. et Alphacheles n. gen. L’assemblage est dominé par des spécimens de C. nicksabani n. sp. (52 % des spécimens identifiables) et E. alabamensis n. comb. (31 %). Trois spécimens de C.nicksabani n. sp. conservent des gonopodes, ce qui est rare. Une analyse de raréfaction indique que (presque) toutes les espèces ont été collectées. Cet assemblage de décapodes du Danien inférieur est le plus diversifié d’Amérique du Nord connu à ce jour et fournit une base pour la poursuite des études sur les décapodes à travers la limite K-Pg. MOTS CLÉS Alabama, Anomura, Axiidea, Brachyura, Crustacea, Danien, Decapoda, Paléocène, combinaisons nouvelles, genres nouveaux, espèces nouvelles. KEY WORDS Alabama, Anomura, Axiidea, Brachyura, Crustacea, Danian, Decapoda, Paleocene, new combinations, new genera, new species. 579 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) GEOLOGICAL SETTING The lower Paleocene (Danian) Clayton Formation in Alabama is divided into a lower (Pine Barren) and upper (McBryde Limestone) members in central Alabama. Toulmin (1977) first documented the macroinvertebrate content of the Pine Barren beds in Alabama (Butler and Wilcox counties). Several localities or cores from central Alabama with Pine Barren sediments have been described including but not limited to the Antioch Church Core (Schulte & Speijer 2009), Braggs (e.g., Jones etal. 1987; Bryan & Jones 1989; Zachos etal. 1989), Mooseland (Larina etal. 2016), Moscow Landing (e.g., Smith 1997; Hart etal. 2013; Savrda etal. 2020), and Mussel Creek (Hart etal. 2013; Udgata & Savrda 2016). Thus, the age of these sediments is generally well constrained. The roadcut at Mussel Creek (ALMNH loc. 3) is in the southern part of Lowndes County, Alabama, United States (Fig. 1). Here, c. 5.5 m of section of the lower Danian Pine Barren Member of the Clayton Formation is exposed and another 1 m can currently be cored with an auger until hitting a limestone layer (Fig. 2). These sediments, all within nannofossil zone NP2, comprise an alternation of gray to tan, carbonaceous, glauconitic calcareous, variably sandy micaceous mudstones and harder limeto marlstone layers (Hart etal. 2013; Udgata & Savrda 2016). Udgata & Savrda (2016) interpreted these layers to represent a highstand systems tract, and these limestones to have formed diagenetically below marine flooding surfaces. Macrofossils from this roadcut include plant remains, asteroid ossicles, bivalves, gastropods, a nautiloid, echinoid spines, bryozoans, a crinoid, decapods, shark and ray teeth, holocephalan teeth, bony fish teeth and vertebrae, crocodile bones and teeth, turtle, and some trace fossils (Figs 3; 4). Among these macrofossils, four decapod species (Feldmann etal. 2014, 2019) and two lamniform shark species (Cicimurri etal. 2020; Ebersole etal. 2024) were formally reported, but many other fossils remain to be studied. Nearly all decapod specimens studied herein originate from the lower middle part of NP2 nannofossil zone (Fig. 2). Older, earliest Danian layers exposed in the stream cut of Mussel Creek have yielded reported macrofossils such as echinoids, bivalves, bryozoans, and burrows such as Thalassinoides Ehrenberg, 1944 (Savrda 1993; Udgata & Savrda 2016; Zachos 2017). MATERIAL AND METHODS In total, 354 identifiable decapod specimens (excluding 30 Axiidean indet. and 25 Decapoda indet.) were collected at the Mussel Creek roadcut (31°58’17”N, 86°42’15”W) in Lowndes County, Alabama, from 2010-2024 during one or multiple trips each year. Most specimens were collected by PGM (2010-2024) and many others by AAK (2021-2024). The specimens were often found loose on the surface, having weathered out of the mudstones and limestones; some specimens were discovered embedded in the rock. The specimens were largely collected from the mudstones above and below the most prominent limestone layer (layer 13 in Figure 2) currently visible at the roadcut (layer 18 of Udgata & Savrda 2016), which is c. 8 m above the K-Pg boundary exposed within the creek bluff based on our measurements. Specimens were prepared using air scribes and hardened with Paraloid B-72 as needed. Specimen photography was done using a Canon EOS 90D camera with a 60 mm lens in an Ortech Photo-e-Box Plus lightbox. Closeup pictures were made using a Swiftcam 18 MP camera mounted on a microscope and using an MP-E 65 mm lens on a Canon EOS 90D camera. Postprocessing of specimen images such as stacking occurred in Adobe Photoshop. A D3D-s (model S2) 3D scanner was used to create 3D models of specimens of new species with the help of Polyga PointKit Scan software. All specimens used are reposited in the museum collections listed below. Specimens only identifiable to high taxonomic ranks (Axiidea indet.: ALMNH:Paleo:5920 [3 specimens], ALMNH:Paleo:5922 [1 specimen], ALMNH:Paleo:13536 [1 specimen], fig. 1. — Images of the roadcut of Mussel Creek, Lowndes County, Alabama, exposing the lower Danian Pine Barren Member (Clayton Formation): A, East side; B, West side. Most of the soft, tan layers have grown over since photos were taken in 2010. The main hard limestone layer (layer 13, c. 8 m above the K-Pg boundary in Figure 2 corresponds to layer 18 of Udgata & Savrda 2016) is barely visible in the lower left corner of A but clearly visible in the lower third of B. Credits: photos by P. George Martin. AB 580 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. and ALMNH:Paleo:21556 [25 specimens]; Decapoda indet.: ALMNH:Paleo:21557 [21 specimens], UF 303812 [1 specimen], UF 303815 [1 specimen], UF 303819 [1 specimen], and UF 303866 [1 specimen]) are not treated further below. Coordinates of localities, where available, use the datum WGS 84 standard. Non-decapod macrofossils were identified with the assistance of comparative material in the ALMNH and MMNS collections and multiple references (Gardner 1935; Toulmin 1977; Cicimurri etal. 2020; Garvie 2021; Ebersole etal. 2024). In the discussion, we compare the diversity of early Danian decapod assemblages globally. We recognize there are younger Danian assemblages (e.g., upper Danian Porters Creek Formation [Rathbun 1935a]; middle Danian Faxe Formation [Jakobsen & Collins 1997; Jakobsen etal. 2020; Klompmaker etal. 2022a]; upper Danian Mexia Clay Member of the Wills Point Formation [Armstrong etal. 2009]), but they are outside the envisioned scope of the discussion. NaNNofossil aNalyses Thirty-two samples were collected throughout c. 6 m of outcrop section exposed at the roadcut of Mussel Creek. The samples were carefully selected across all lithologies; thus, samples were collected in both the intervals of mudstone and beds of limestone/marl. The calcareous nannofossils were studied under cross-polarized light and phase contrast at 1000X magnification, using a Zeiss Axiophot light microscope (LM). The samples were prepared for LM observation using a routine smear slide technique. Samples were analyzed quantitatively to identify biostratigraphic events and establish a nannofossil zonation for the section, and to document nannofossil-assemblage changes throughout the early Danian. Quantitative analysis involved counting 300 nannofossil specimens from random fields of view. In general, reaching a count of 300 specimens required observation of between 1-2 traverses. However, samples marked by very low nannofossil abundances would sometimes require viewing of up to five traverses. The abundances of each species were also recorded using the following categories: SA (super-abundant) = > 75 specimens, A (abundant) = 21-75 specimens, C ( common) = 9-20 specimens, F (few) = 4-8 specimens, and R (rare) = 1-3 specimens. The biostratigraphic interpretation of the samples utilized the nannofossil biozonation of Martini (1971), and the associated numeric ages of zonal boundaries and nannofossil bioevents are derived from Gradstein etal. (2012). We use the terms “Base” for the first or lowest stratigraphic occurrence of a species, and “Top” for the last or highest stratigraphic occurrence. The terminology for abundance-based bioevents includes the following: “increase” = frequent-common; “influx” = abundant; “major influx” = super-abundant; “acme” = acme, or absolute highest abundance. Of taxonomic and biostratigraphic note is that although Cruciplacolithus tenuis (Stradner, 1961) is the traditional and official index species representing Zone NP2, we acknowledge the serious taxonomic problem (e.g., cross bar with “feet-like” terminations) associated with the use of Base C. tenuis as the zonal marker defining NP2. In this study, we follow the historical taxonomic concept/biostratigraphic approach used by others (Perch-Nielsen 1985; Van Heck & Prins 1987; Varol 1989; Bown etal. 2023). As such, we consider Base Cruciplacolithus intermedius Van Heck & Prins, 1987, the bioevent and substitute zonal marker defining Zone NP2. We consider Zones NP1-NP2 to represent the “lower”/”early” Danian here informally. Slides with nannofossils are stored at the Geological Survey of Alabama. iNstitutioNal abbreviatioNs ALMNH Alabama Museum of Natural History paleontology collection, University of Alabama, Tuscaloosa, Alabama; GSA Geological Survey of Alabama, Tuscaloosa, Alabama; MGSB Museu Geològic del Seminari de Barcelona, Barcelona; MMNS IP Mississippi Museum of Natural Science Invertebrate Paleontology collection, Jackson, Mississippi; NPL Non-vertebrate Paleontology lab, Jackson School Museum of Earth History, University of Texas at Austin, Austin, Texas; UF Florida Museum of Natural History (Invertebrate Paleontology), University of Florida, Gainesville, Florida. SYSTEMATIC PALAEONTOLOGY Order DECAPODA Latreille, 1802 Infraorder AXIIDEA de Saint Laurent, 1979 Family CteNoChelidae Manning & Felder, 1991 iNCluded geNera. — Ahazianassa Karasawa, Kishimoto, Ohara & Ando, 2019; Alphacheles n. gen.; Ctenocheles Kishinouye, 1926; Cretagourretia Ossó, Charbonnier, Hyžný, Van Bakel, Devillez, Bover-Arnal & Moreno-Bedmar, 2024; Ctenocheloides Anker, 2010; Dawsonius Manning & Felder, 1991; Gourretia de Saint Laurent, 1973; Kiictenocheloides Sakai, 2013; Laurentgourretia Sakai, 2004; Paragourretia Sakai, 2004. Genus Alphacheles n. gen. urn:lsid:zoobank.org:act:D5A2F0B5-3E68-403C-A751-6951DE740D9F type speCies. — Callianassa zeta Rathbun, 1936 (Callianassa alpha Rathbun, 1935a; non Callianassa alpha Stenzel, 1935), by present designation. etymology. — The genus name is a combination of “alpha”, referring to the homonymous species name Callianassa alpha, and “cheles” meaning “claw”. Gender: masculine. diagNosis. — As for the type species. remarks Shortly after the description of Callianassa alpha Rathbun, 1935a, it was revealed that the name had already been used by Stenzel (1935) for yet another fossil ghost shrimp assigned to Callianassa. A rectification was published in the following year, renaming C. alpha to C. zeta Rathbun, 1936. 581 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) Callianassa zeta differs from all known extant and extinct ghost shrimp taxa by its tuberculate area (“densely punctate excrescence” sensu Rathbun [1935a]; “triangular patch of granules” sensu Feldmann etal. [2019]) at the base of the fixed finger which is present at the outer and inner lateral surfaces. This character has been considered a diagnostic feature of this species (Rathbun 1935a; Feldmann etal. 2019). Its taxonomic significance is herein elevated to the genus level, and hence a new genus is proposed to accommodate this species. So far, only propodi and dactyli are known for Alphacheles zeta (Rathbun, 1936) n. comb. Most specimens represent major claws, whereas in one case also a minor claw is identified (Fig. 5O). Their morphology is rather close to that of extant species of Gourretia and Paragourretia, based on which the new genus is classified within the family Ctenochelidae. Nevertheless, the familial placement of Alphacheles n. gen. should be considered preliminary until more complete material is found. Alphacheles n. gen. shares with the above-mentioned genera the following set of characters: major cheliped propodus distinctly longer than high and subrectangular in outline, relatively long fingers exceeding half of the propodus palm length, and dactylus occlusal surface with simple dentition (cf. Le Loeuff & Intès 1974; Sakai 2002, 2004; Ngoc-Ho 2003). These characters are shared also with Cretagourretia, an exclusively fossil genus known from the Early Cretaceous (Albian) of Spain. This set of characters mentioned above is rarely seen in other ghost shrimp families (Poore & Ahyong 2023). As mentioned above, Alphacheles n. gen. differs from all ghost shrimp genera known to date by the presence of a tuberculate area at the base of the fixed finger. It differs also from yet another exclusively fossil ctenochelid genus, Ahazianassa, from the Late Cretaceous (Maastrichtian) of Japan. Additionally, Alphacheles n. gen. possesses a more elongate palm than Ahazianassa does. Besides Callianassa alpha, Rathbun (1935a) described also “C. alpha var.” from the Upper Eocene Jackson Group of Mississippi. A new variety of C. alpha is based on a single incomplete propodus and a pleon found at the same locality. fig. 2 . — Stratigraphic column of the Mussel Creek roadcut relative to the K-Pg boundary within the creek, nannofossil zonation and key species based on microfossil samples (red dots), and layers in which nearly all decapods were found. 1 20 14 15 45 6 2 3 7 8 9 10 11 12 13 16 17 18 19 21 22 23 24 25 26 27 11 10 9 8 7 6 5 Height of section (meters above K-Pg boundary) upper NP2 middle NP2 lower NP2 Base Praeprinus dimorphosus [common] Base Cruciplacolithus primus [super-abundant/acme] Base Cruciplacolithus intermedius [common] Base Praeprinus dimorphosus, Top Futyania spp. [abundant] Base Lanternithus duocavus [frequent] Top Cyclagelosphaera alta [frequent] Top Cyclagelosphaera alta [abundant] Top Futyania spp. [super-abundant], Top Futyania attewellii [acme], Top Braarudosphaera spp. [abundant] Base Praeprinsius tenuiculus, Base Neocrepidolithus dirimosus, Base Zeugrhabdotus sigmoides [common] Base Cruciplacolithus intermedius, Base Coccolithus pelagicus, Base Futyania spp. [super-abundant] 582 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. fig. 3 . — Non-decapod body macrofossils from the lower Danian Pine Barren Member (Clayton Formation) found at the roadcut of Mussel Creek, Lowndes County, Alabama: A, Crocodylia vertebra (ALMNH:Paleo:21546); B, Crocodylia osteoderm fragment (ALMNH:Paleo:21538); C, Crocodylia tooth (ALMNH:Paleo:22081A); D, anterolateral shark tooth of Mennerotodus mackayi Cicimurri, Ebersole & Martin, 2020 (ALMNH:Paleo:21532); E, (para-)symphyseal shark tooth of Mennerotodus mackayi (ALMNH:Paleo:21523); F, turtle femur (ALMNH:Paleo:21547); G, wood fragment (ALMNH:Paleo:21534); H, lateral shark tooth of Palaeohypotodus speyeri (Dartevelle & Casier, 1943) (ALMNH:Paleo:21524); I, vomerine with some teeth of bony fish cf. Pycnodus sp. (ALMNH:Paleo:21543); J, molariform tooth of bony fish cf. Pycnodus sp. (ALMNH:Paleo:21522); K, vertebra of bony fish (ALMNH:Paleo:21545); L, bivalve Cucullaea (?) sp. (ALMNH:Paleo:21530); M, right oyster valve of Ostrea crenulimarginata Gabb, 1860 (ALMNH:Paleo:21520); N, left oyster valve of Gryphaeostrea vomer (Morton, 1828) (ALMNH:Paleo:21533); O, right oyster valve of Gryphaeostrea vomer (ALMNH:Paleo:21535); P, left valve of bivalve cf. Eomiltha sp. (ALMNH:Paleo:21544); Q, bivalve Callocardia sp. (ALMNH:Paleo:21541); R, bivalve Venericardia (Baluchicardia) sp. (ALMNH:Paleo:21519); S, bivalve Crassatella cf. C. ioannes Gardner, 1935 (ALMNH:Paleo:21539). Scale bars: A, B, F, L, Q-S, 10.0 mm; C, D, G-I, K, M-P, 5.0 mm; E, J, 2.0 mm. Credits: photos by Adiël A. Klompmaker. B C DE FG H IJKL MN O P QRS A 583 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) fig. 4 . — Non-decapod body and trace macrofossils from the lower Danian Pine Barren Member (Clayton Formation) found at the roadcut of Mussel Creek, Lowndes County, Alabama: A, gastropod Kapalmerella sp. (ALMNH:Paleo:21526); B, gastropod Mesalia cf. M. hardemanensis (Gabb, 1860) (ALMNH:Paleo:21515); C, gastropod Straticostatum (Paginacosta) sp. (ALMNH:Paleo:21516); D, gastropod Fasciolariidae Gray, 1853 (ALMNH:Paleo:21525); E, gastropod Volutocorbis cf. V. rugatus (Conrad, 1860) (ALMNH:Paleo:21521); F, gastropod Naticidae Guilding, 1834 (ALMNH:Paleo:21540); G, echinoid spine of Cidaroida Claus, 1880 (ALMNH:Paleo:21537); H, I, Crinoidea Miller, 1821 (ALMNH:Paleo:21527); J, Bryozoan Heteroconopeum damicornis (Canu & Bassler, 1920) (ALMNH:Paleo:21531); K, Clionid sponge boring trace (infilling) Entobia isp. (ALMNH:Paleo:21529); L, oyster Gryphaeidae Vialov, 1936 (Pycnodontinae) with drill hole (Oichnus paraboloides Bromley, 1981) by predatory gastropod (ALMNH:Paleo:21536); M, N, Nautiloid Hercoglossa sp. (ALMNH:Paleo:22082); O, four ray teeth of Myliobatis sp. (ALMNH:Paleo:9737); P, Holocephalian Ischyodus williamsae Case, 1991 (ALMNH:Paleo: 9739). Scale bars: A-C, E, F, J, K, P, 5.0 mm; D, M-O, 10.0 mm; G-I, L, 2.0 mm. Credits: photos by Adiël A. Klompmaker. CD E F G HI J K L AB MN OP 590 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. desCriptioN Cheliped merus oval in outline, 1.6 times as long as high; outer lateral surface with longitudinal ridge at mid-height; lower margin distinctly convex, smooth. Cheliped carpus 1.5 times as high as length at upper margin; proximal margin rounded; distolateral margin square at lower angle. Cheliped propodus palm approximately as high as length at upper margin, highest proximally; proximo-lower corner rounded; upper and lower margins carinate, carinae accompanied with rows of setal pores on both sides (inner and outer), carina on lower margin forming microdenticles distally (along fixed finger); inner lateral surface with numerous setal pores concentrated close to distal margin and forming subvertical irregular row; outer lateral surface with setal pores concentrated distally, highest number of pores present close to junction with fixed finger; distal margin of outer lateral surface with blunt tooth just below articulation with dactylus. Fixed finger approximately as long as upper palm length, broadly oval in cross section; outer lateral surface with oblique longitudinal ridge, numerous setal pores scattered below ridge and in row above it along entire fixed finger length; fixed finger occlusal surface with proximal blunt tooth, entire occlusal surface (incl. proximal tooth) with numerous equally sized denticles, tip slightly bent upward. Dactylus upper margin straight, carinate; outer lateral surface with rows of setal pore clusters along upper and occlusal margins; inner lateral surface with several setal pore clusters along mid-length; occlusal surface of robust dactylus morphotype with proximal blunt tooth followed with finely denticulated edge; occlusal surface of slender dactylus morphotype without proximal tooth; dactylus tip slightly bent. fig. 10. — Eucalliaxiopsis alabamensis (Rathbun, 1935a) n. comb. from the lower Danian Pine Barren Member (Clayton Formation) at the roadcut of Mussel Creek, Lowndes County, Alabama (MMNS IP-7251): A, right major cheliped with, from left to right, the merus, carpus, propodus, and dactylus; B, counterpart. In situ nodule with specimen found c. 9.8 m above K-Pg boundary. Scale bars: 10.0 mm. Credits: photos by Adiël A. Klompmaker. A B 591 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) remarks Rathbun (1935a: pl. 15.7-15.10) figured two type specimens, the dactylus paratype, which received a new number subsequently (USNM PAL 327231 A), but she also mentioned the presence of more specimens (20 propodi and three fingers). Five additional specimens (USNM PAL 327231) are listed as paratypes in the Smithsonian Institution database and seen by AAK in 2018, but another catalog number used in Rathbun (1935a) (371504) does not return any match in their database. Thus, the whereabouts of 16 original specimens is uncertain. Newly collected specimens match the type material in most details. Slight differences relate to the mode of preservation. The type specimens are partly abraded hindering the observation of minute details while the cuticular surfaces are better preserved in the newly collected material. For instance, the development of microdenticles on the lower margin of the propodus, the dentition on the occlusal edges of fingers and morphological details of setal pores are not well observable in the type material. Setal pores are arranged in clusters; the clusters are oval, distinctly elongate or V-shaped. Elongate setal pore clusters, oriented perpendicularly to the occlusal margin, are present especially on the outer lateral surface of dactyli, whereas V-shaped clusters are sometimes present on the outer lateral surface of the fixed fingers. The number of setal pores/setal pore clusters slightly varies when comparing the same parts of various specimens. There are two morphotypes of dactyli identified in the newly collected material: the robust one, with the proximal tooth on the occlusal surface, and the slender one, without the respective tooth. The slender morphotype is interpreted to belong to a minor claw, whereas the robust morphotype is interpreted to belong to a major claw; such differences in the morphology of cheliped dactyli are known also in extant species of Eucalliacidae (Poore 2021). Based on the presence of a proximal tooth on the occlusal surface of the fixed finger, all studied propodi attributed to E. alabamensis n. comb. are interpreted to belong to major claws only; such a proximal tooth is missing in minor claws of eucalliacid shrimps (Hyžný 2012; Hyžný & Hudáčková 2012; Poore 2021). Major chelipeds are sexually dimorphic in representatives of Eucalliaxiopsis, with males having the propodus palm proportionally longer than that of females (Poore 2021). The limited number of complete propodi does not allow an evaluation of this dimorphism in E. alabamensis n. comb., although one propodus (Fig. 8F, G) indeed appears to be proportionally longer than others and might represent a male individual. The newly presented material of E. alabamensis n. comb. is the second report of the species, originally described nearly a century ago (Rathbun 1935a). It also adds further details to the description of the species, especially the morphology of the carpus and merus, previously unknown for this taxon. The range of the species is expanded from the late Danian to the early Danian. From fossil congeners, Eucalliaxiopsis alabamensis n. comb. differs from E. pseudorakosensis mainly in the nature of major dactylus. In E. pseudorakosensis, the occlusal margin of the dactylus is armed with a distal tooth (Hyžný & Hudáčková 2012), which is entirely missing in E. alabamensis n. comb. Infraorder ANOMURA MacLeay, 1838 Superfamily paguroidea Latreille, 1802 Family ?diogeNidae Ortmann, 1892 Genus ?Paguristes Dana, 1851 type speCies. — Paguristes hirtus Dana, 1851, by subsequent designation (Stimpson 1858: 235). “Paguristes” johnsoni Rathbun, 1935a (Fig. 11) Paguristes johnsoni Rathbun, 1935a: 78, pl. 14.13-14.18. — Cope etal. 2005: 101, pl. fig. 6.2. t ype material . — Holotype. United States • Alabama, Wilcox County, Prairie Creek and Pine Barren section; Porters Creek Formation; Paleocene (upper Danian); USNM MO 371705 (right propodus). Paratype. United States • 1 specimen; same as for the holotype; USNM MO 371706 (left minor propodus and dactylus). additioNal material examiNed. — United States • 1 specimen; Alabama, Lowndes County, Mussel Creek roadcut (31°58’17”N, 86°42’15”W), ALMNH loc. 3; Clayton Formation, Pine Barren Member, lower middle NP2 nannofossil zone; Paleocene (lower Danian); ALMNH:Paleo:21483 (right propodus + base of dactylus) • 1 specimen; idem; ALMNH:Paleo:21484 (left dactylus) • 1 specimen; idem; ALMNH:Paleo:21485 (right dactylus) • 1 specimen; idem; ALMNH:Paleo:21486 (?left fixed finger) • 1 specimen; idem; ALMNH:Paleo:21487 (right dactylus) • 1 specimen; idem; ALMNH:Paleo:21555 (left merus) • 1 specimen; idem; UF 303860 (right dactylus) • 1 specimen; Alabama, Sumter County, Tombigbee River, Black Bluff (32°22’22”N, 88°2’38”W), ALMNH loc. 5; Porters Creek Formation; Paleocene (upper Danian); ALMNH:Paleo:21495 (right propodus) • 1 specimen; idem; ALMNH:Paleo:21496 (right dactylus) • 1 specimen; idem; GSA-I21012 (right dactylus) • 1 specimen; Alabama, Wilcox County; Porters Creek Formation; Paleocene (upper Danian); GSA-I20984 (right propodus). type horizoN. — Porters Creek Formation (Sucarnoochee beds in Rathbun 1935a), upper Danian. type loCality. — Prairie Creek and Pine Barren section, Wilcox County, Alabama, United States. diagNosis. — Major palm short; about as long as high; tubercles with pit in center; diamond-shaped in cross-section; with sharp, convex upper and lower margins; upper margin shorter than lower margin; rounded ridges on outer and inner sides. Major dactylus with tubercles with pit in center and non-tubercular patches with setal pores on outer, upper, and part of inner sides; occlusal surface with a few large teeth and a smaller tooth on outer side of first tooth proximally, and a row of connected small teeth toward distal end. measuremeNts. — Palm length (mm): ALMNH:Paleo:21483: 5.4 (as preserved); USNM MO 371705: 15.6; ALMNH:Paleo:21495: 10.4; GSA-I20984: 10.6 (as preserved). 592 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. desCriptioN Reference is made to Rathbun (1935a: 78). Additionally: major dactylus curved inward; tubercles with pit in center and non-tubercular patches with setal pores on outer, upper, and part of inner sides; occlusal surface with a few large teeth and a smaller tooth on outer side of first tooth proximally, and a row of connected small teeth toward distal end. remarks The single right propodus available (ALMNH:Paleo:21483) from Mussel Creek is incomplete but closely resembles the holotype of Paguristes johnsoni (USNM MO 371705, right propodus) and other right propodi (ALMNH:Paleo:21495, right propodus; GSA-I20984, right propodus) from the upper Danian Porters Creek Formation in Alabama in terms of overall shape, size, and distribution of the ornamentation, and the ridge on the outer surface. The base of the dactylus is preserved along with the propodus from Mussel Creek (ALMNH:Paleo:21483), showing the base of the first large tooth and an adjacent small accessory tooth on the outer side that large tooth. This pattern resembles other isolated dactyli from Mussel Creek and dactyli from the Porters Creek Formation (ALMNH:Paleo:21496, GSA-I21012), which allows us to assign these specimens to P. johnsoni as well. The sample also contains an isolated finger that could be a fixed finger of this taxon (Fig. 11I, J). It contains a row of small teeth on the occlusal surface and might belong to the minor claw of this taxon because large teeth on the occlusal surface are often seen on both fingers of the major claw in paguroids, whereas small teeth are often seen on the minor claw in paguroids (e.g., Forest etal. 2000). The oblique row of small teeth on its inner proximal part matches that of the base of the fixed finger of the propodus (ALMNH:Paleo:21483). Dactyli of the major claw were unknown from this species thus far. A left merus possibly belonging to the same species was also found (ALMNH:Paleo:21555). This species was briefly discussed in Bishop (1983: 419), citing a personal communication with Jaques Forest, who was in doubt that Paguristes whitteni Bishop, 1983, and P.johnsoni could be assigned to Paguristes or even paguroids. Tubercular propodi do not necessarily imply a paguroid affinity. Indeed, the propodi of Paguristes whitteni belong to carapace specimens of the brachyuran crab Dakoticancer australis Rathbun, 1935a (see Kornecki etal. 2017), also common at the same locality in Mississippi. We cannot assign the tubercular elements herein to a brachyuran carapace from the same assemblage. The dactyli and propodi are too large for Alahexapus martini (Feldmann, Schweitzer & Portell, 2014) n. comb. and the (distal) cheliped elements of other brachyuran taxa (see below) do not resemble the propodi/dactyli of P. johnsoni. The cheliped elements also cannot be linked to a brachyuran carapace from the Porters Creek Formation. Given the extensive collecting efforts at the Mussel Creek roadcut since 2010, the likelihood of finding other brachyuran taxa to which the claw elements could belong is low. We therefore suggest that the specimens represent a paguroid. The fact that the right propodus is larger than the left propodus (see Rathbun 1935a: pl. 14.13-14.17), if both isolated elements are indeed from the same species, is inconsistent with Diogenidae, members of which usually have a larger left propodus or (sub)equal propodi (e.g., Tudge etal. 2012: 305), including Paguristes, which is mentioned to have isochelous propodi (Fraaije etal. 2015: 590). An exception within diogenids is Petrochirus Stimpson, 1858, but this taxon has scabrous ornamentation in the type species Petrochirus diogenes (Linnaeus, 1758) (see Hyžný & Dulai 2021: fig. 43.7) not seen in P. johnsoni and various fossil Petrochirus (Beschin etal. 2002, 2006, 2012). The dactyli herein closely resemble a dactylus identified as Petrochirus sp. from the Early Miocene of Venezuela (Feldmann & Schweitzer 2004: pl. 1.2-1.4), but this record has more teeth on the occlusal surface. It is likely these species belong to the same genus. We have not found close matches with other Petrochirus spp. More complete material with both left and right cheliped would be necessary to further evaluate the genus and family placement. For now, we treat the specimens as “Paguristes” johnsoni within Paguroidea. The assignment of our material to P. johnsoni implies a range extension into the early Danian in Alabama. Cope etal. (2005) ascribed a propodus from the Clayton Formation of southern Illinois to P. johnsoni. The level of this specimen within the Clayton Formation was not reported, but potassium-argon dating on glauconite on the oldest sample from the Clayton Formation returned a date of 60.6 ± 1.3 Ma (Reed etal. 1977). This date suggests it is not the earliest Danian and that this propodus from Illinois is probably younger than the specimens herein. Infraorder BRACHYURA Linnaeus, 1758 Section RANINOIDA De Haan, 1839 [in 1833-1850] Superfamily raNiNoidea De Haan, 1839 [in 1833-1850] Family raNiNidae De Haan, 1839 [in 1833-1850] Subfamily raNiNoidiNae Lőrenthey in Lőrenthey & Beurlen, 1929 Genus Raninoides H. Milne Edwards, 1837 [in 1834-1840] type speCies. — Ranina laevis Latreille, 1825, by monotypy. i NCluded speCies . — Extant species: Raninoides benedicti Rathbun, 1935b; R. bouvieri Capart, 1951; R. crosnieri Ribes, 1989; R.hendersoni Chopra, 1933; R. intermedius Dai & Xu, 1991; R.laevis (Latreille, 1825); R. lamarcki A. Milne Edwards & Bouvier, 1923; R.longifrons Chen & Türkay, 2001; R. louisianensis Rathbun, 1933; R.personatus Henderson, 1888. Exclusively fossil species: R.acanthocolus Schweitzer, Feldmann, González-Barba & Cosovic, 2006; R.araucana (Philippi, 1887); R.asper Rathbun, 1926; R. borealis (Collins & Wienberg Rasmussen, 1992); R. budapestiniensis (Lőrenthey, 1897); R. danicus n. sp.; R.dickersoni Rathbun, 1926; R. eugenensis Rathbun, 1926; R.fabianii (Lőrenthey in Lőrenthey & Beurlen, 1929); R.fulgidus Rathbun, 1926; R.fulungensis Hu & Tao, 1999; R.glabra (Woodward, 1871); R.goedertorum (Tucker, 1998); R.gottschei (Böhm, 1927); R.granulofrons Vega, Nyborg, Garassino, Pasini, Aguilar-Pérez, Borges-Sellén, Arano-Ruiz, QuinteroVázquez & 593 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) Gutiérrez-Domech, 2024; R. hollandica (Collins, Fraaye, Jagt & Van Knippenberg, 1997); R. javanus (Böhm, 1922); R.madurensis Beets, 1950; R. mexicanus Rathbun, 1930; R. morrisi Collins, Lee & Noad, 2003; R. notopoides (Bittner, 1883); R. oregonensis Rathbun, 1926; R. perarmata (Glaessner, 1960); R.pliocenicus De Angeli, Garassino & Pasini, 2009; R.proracanthus Schweitzer, Feldmann, González-Barba & Cosovic, 2006; R. pulchra (Beschin, Busulini, De Angeli & Tessier, 1988); R. rathbunae Van Straelen, 1933; fig. 11 . — “Paguristes” johnsoni Rathbun, 1935a, from the lower Danian Pine Barren Member (Clayton Formation) at the roadcut of Mussel Creek, Lowndes County, Alabama (A-N), the upper Danian Porters Creek Formation at Black Bluff, Sumter County, Alabama (O, Q, R), and the upper Danian Porters Creek Formation in Wilcox County, Alabama (P): A, B, outer and inner views of right propodus (ALMNH:Paleo:21483); C, D, bases of fixed finger and dactylus (ALMNH:Paleo:21483); E-H, outer, inner, occlusal, and upper margin views of right dactylus (ALMNH:Paleo:21487); I, J, inner and occlusal views of possible left fixed finger (ALMNH:Paleo:21486); K-N, outer, inner, lower, and proximal views of left merus (ALMMH:Paleo:21555); O, P, outer views of right propodi (ALMNH:Paleo:21495 and GSA-I20984); Q, R, occlusal views of right dactyli (GSA-I21012 and ALMNH:Paleo:21496). Scale bars: 2.0 mm. Credits: photos by Adiël A. Klompmaker. ABC D EFG H KL MN OPQ R IJ 594 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. R.rioturbiensis Schweitzer, Feldmann, Casadío & Raising, 2012; R.sinuosus (Collins & Morris, 1978); R. slaki Squires, 2001; R.treldenaesensis Collins & Jakobsen, 2003; R.vaderensis Rathbun, 1926 (Laeviranina lewisana Rathbun, 1926); R. toehoepae (Van Straelen, 1924); R.washburnei Rathbun, 1926. diagNosis. — See Karasawa etal. (2014: 258). Raninoides danicus n. sp. (Figs 12; 13; Appendices 1I, J; 2) urn:lsid:zoobank.org:act:6B1972E9-782E-4B4C-AC4A-2BEAA49CC8CE Giulianolyreidus johnsoni (Rathbun, 1935a). — Feldmann etal. 2019: 285, fig. 5. t ype material . — Holotype. United States • 1 specimen; Alabama, Lowndes County, Mussel Creek roadcut (31°58’17”N, 86°42’15”W), ALMNH loc. 3; Clayton Formation, Pine Barren Member, lower middle NP2 nannofossil zone; Paleocene (lower Danian); ALMNH:Paleo:21488. Paratypes. United States • 1 specimen; same as for the holotype; ALMNH:Paleo:5919 • 1 specimen; idem; ALMNH:Paleo:21489 • 1 specimen; idem; ALMNH:Paleo:21490 • 1 specimen; idem; ALMNH:Paleo:21491 • 1 specimen; idem; ALMNH:Paleo:21492. etymology. — danicus refers to the first species of Raninoides recognized from the Danian. additioNal material examiNed. — United States • 5 specimens; Alabama, Lowndes County, Mussel Creek roadcut (31°58’17”N, 86°42’15”W), ALMNH loc. 3; Clayton Formation, Pine Barren Member, lower middle NP2 nannofossil zone; Paleocene (lower Danian); ALMNH:Paleo:21493 • 1 specimen; idem; ALMNH:Paleo:21494 • 2 specimens; idem; MMNS IP-7252 • 4 specimens; idem; MMNS IP-7253 • 1 specimen; idem; MMNS IP-8792 • 1 specimen; idem; UF 303873. type horizoN. — Pine Barren Member of the Clayton Formation, middle NP2 nannofossil zone, lower Danian. type loCality. — ALMNH loc. 3: Mussel Creek roadcut (31°58’17”N, 86°42’15”W), Lowndes County, Alabama, United States. diagNosis. — Carapace length-width ratio c. 1.45 without rostrum and spines. Fronto-orbital width c. 70% of maximum width; posterior margin 70% of maximum width. Front with outer orbital spine curving inward to form straight part, lined with tubercles; intra-orbital spine surrounded by deep fissures, outer part top of spine steep-sided and lined with tubercles; outermost part rostral section of front concave, lined with tubercles. Anterolateral margin with one strong spine near outer orbital angle and directed anterolaterally, otherwise mostly straight and lined with tubercles. Sinuous band of tubercles just posterior to frontal margin. Sternite 4 longer than wide. measuremeNts. — Maximum carapace width (mm): ALMNH:Paleo:21488: 12.3, ALMNH:Paleo:5919: 14.7, ALMNH:Paleo:21490: 12.3, MMNS IP-7252.1: 15.1, MMNS IP-7253.1: 8.8. desCriptioN Carapace longer than wide (l/w ratio c. 1.45 without rostrum and spines), moderately vaulted transversely, weakly vaulted longitudinally, widest around third of length. Fronto-orbital width c. 70% of maximum width; posterior margin 70% of maximum width. Front incompletely known, but with outer orbital spine curving inward to form straight part, lined with tubercles; intra-orbital spine surrounded by deep fissures, outer part top of spine steep-sided and lined with tubercles; outermost part rostral section of front concave, lined with tubercles. Suborbital margin lined with tubercles, mostly straight except near outer orbital spines and with single deep fissure. Orbit wider than tall. Anterolateral margin with one strong spine near outer orbital angle and directed anterolaterally, otherwise mostly straight and lined with tubercles; convex transition to mostly straight and longer posterolateral margin lined with tubercles. Convex transition from posterolateral margin to posterior margin, which exhibits a slight concavity axially and is smoothrimmed. Axis of carapace with weak, rounded ridge. Carapace regions undefined, except for lateral parts of cardiac region in between concave-outward branchiocardiac grooves. Pair of posterior gastric pits in front of branchiocardiac grooves. Cuticle of dorsal carapace with widely spaced deep pits and more dense shallow pits, but with sinuous band of tubercles just posterior to frontal margin. Pterygostome with gentle ridge anteriorly, widening anteriorly, with sinuous buccal collar, with tubercular cuticle, uninterrupted transition to branchiostegite. Sternite 3 small, rounded laterally, with sharp tip and steep front; sternite 4 longer than wide, with concave lateral sides, episternites rounded; sternite 5 about equally long as wide, widening toward sternite 4, with axial groove; sternite 6 widening posteriorly, with concave posterior margin on either side of axis, with axial groove. Sternites 3-4 cuticular surface pitted but with tubercles along margins; tubercles on lateralmost parts of sternites 5 and 6 in dorsal view, and on transition from sternite 5 to 6. Pleurites 4-7 partly visible externally, smooth cuticular surface except for pleurite 4 and spines on pleurites 4-7 containing tubercles; pleurites with rims around pereiopod attachments. Coxae of maxilliped 3 curved forward, adjacent to lateral sides sternite 3. Oval attachment of cheliped pair to venter, circular for second pereiopod pair. Rostrum, pleon, and appendages not preserved. remarks Feldmann etal. (2019) ascribed three carapaces (MMNS IP-7252 [2 specimens] and MMNS IP-8792) to Giulianolyreidus johnsoni within Lyreidinae Guinot, 1993. The dorsal carapace is close to this species first described from the upper Danian Porters Creek Formation of Alabama (Rathbun 1935a: pl. 17.12-17.17 [as Symethis johnsoni]; Bishop & Whitmore 1986: fig. 1K [not 1G, 1H, 1J]; Waugh etal. 2009: fig. 11; Karasawa etal. 2014: fig. 12C, D) and later from the upper Danian Mexia Clay Member of the Wills Point Formation in Texas (Armstrong etal. 2009: fig. 4.1-4.2 [as Macroacaena johnsoni] [identification verified by AAK]), but the axial ridge is more prominent and the pits on the cuticular surface are larger in G. johnsoni. Moreover, the ventral side of multiple new specimens (ALMNH:Paleo:5919, ALMNH:Paleo:21488-21490, ALMNH:Paleo:21494) and MMNS IP-8792 show marked differences, revealing an axial groove 595 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) on sternites 5 and 6 (Figs 12B; 13A, which G. johnsoni lacks (Rathbun 1935a: pl. 17.12). Comparable dorsal and ventral surfaces are found among Raninoidinae, such as Notosceles Bourne, 1922, and Raninoides. The main differences between these genera involve the development of the rostrum, orbital fissures, and the outer orbital spines (diagnoses in Karasawa fig. 12. — Raninoides danicus n. sp. from the lower Danian Pine Barren Member (Clayton Formation) found at the roadcut of Mussel Creek, Lowndes County, Alabama: A-D, dorsal, ventral, right lateral, and frontal views of holotype ALMNH:Paleo:21488; E, dorsal view of paratype ALMNH:Paleo:21492; F, dorsal view, focused on the left frontal margin, of paratype ALMNH:Paleo:21491; G-I, right orbital, upper orbital margin, and lower orbital margin views of paratype ALMNH:Paleo:5919. Scale bars: A-E, 5.0 mm; G-I, 2.0 mm. Credits: photos by Adiël A. Klompmaker. EF G HI ABC D 596 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. etal. 2014, and Schweitzer etal. 2018b), but these features are not wellpreserved in the specimens from Mussel Creek. Karasawa etal. (2014) diagnosed that Notosceles exhibits short open fissures, but one specimen herein (ALMNH:Paleo:21491) exhibits fairly deep fissures (Fig. 12F). An additional difference we noted is that the anterolateral spine is substantially larger and more anterolaterally directed in Raninoides than in Notosceles, in which a small spine is consistently more forwardly directed across all species (see extant species and Notosceles bournei Rathbun, 1928, from the Paleocene of Texas, Alabama, and Arkansas, see Rathbun 1935a). Many extant and fossil Raninoides have a strong anterolaterally directed spine, consistent with our specimens. This genus is diagnosed to exhibit a bifid outer orbital spine (Karasawa etal. 2014; Schweitzer etal. 2018b), but this does not apply to all species assigned to this genus because several members have a straight plateau inward from a single spine rather than another spine (e.g., Paleocene R.borealis, extant R. crosnieri, extant R. longifrons, and extant R.personatus). None of the fossil specimens studied here have the tip of the outer orbital spine preserved, but two specimens show a straight plateau inward in addition to the base of the outer orbital spine (ALMNH:Paleo:5919 and MMNS-IP7253.2). Thus, we assign the specimens to Raninoides with confidence. Reasons for species separation often include the orientation, size, and location of the anterolateral spine; the development of the frontal margin and post-frontal ridge, and carapace proportions (e.g., Collins etal. 2003; Schweitzer etal. 2006, 2012; De Angeli etal. 2009). The early Danian Raninoides danicus n. sp. differs from all other species. The stratigraphically closest species are R. borealis from the middle Paleocene (Selandian) of West Greenland and R. granulofrons from the late Campanian-early Maastrichtian of Cuba. Based on a study of the type material by AAK, R. borealis bears an anterolateral spine that may be farther from the outer orbital margin, this spine is oriented more forward, and the intra-orbital spine is more rounded. Raninoides granulofrons bears an intra-orbital spine that is more rounded on top, and the preserved base of the anterolateral spine is smaller, mentioned to be short by Vega etal. (2024). We also compared this species to Eocene species, using the papers in which those species were first described and other papers as needed. Raninoides acanthocolus bears a shorter anterolateral spine further back on the anterolateral margin and the upper margin of the intraorbital spine slopes inward (Schweitzer etal. 2006: fig. 2.7). Raninoides araucana bears a smaller anterolateral spine (Philippi 1887: pl. 50.6). Raninoides budapestiniensis has an anterolateral spine further back on the anterolateral margin and a stronger postfrontal ridge (Lőrenthey 1898: pl. 1.2). Raninoides dickersoni, only known from a venter, has a wider spine on sternite 5 (Rathbun 1926: pl. 20.5). Raninoides fabianii apparently lacks anterolateral spines (Lőrenthey & Beurlen 1929: pl. 4.10). Raninoides fulgidus has a proportionally smaller anterolateral spine (Rathbun 1926: pl. 23.6; ALMNH:Paleo:5937). Raninoides glabra has the axial groove more forward onto the posterior part of sternite 4 (near the center of episternite 4) and sternite 4 is proportionally longer (see Van Bakel etal. 2012: fig. 44c, d). Raninoides goedertorum and R.notopoides exhibit smaller and more forwardly oriented anterolateral spines (Tucker 1998: fig. 13; Hyžný & Zorn 2016: pl. 9.3). Raninoides gottschei has a smaller anterolateral spine (Glaessner & Withers 1931: pls 20.1-2, 21.1). Raninoides perarmata and R. rathbunae have proportionally shorter sternites 4 (Feldmann 1991: figs 2, 4; Feldmann & Schweitzer 2004: fig. 1B). Raninoides proracanthus bears a much smaller anterolateral spine (Feldmann & Schweitzer 2004: fig. 2.8). Raninoides pulchra exhibits an anterolateral spine that is bifid near its base (Beschin etal. 1988: pl. 4.1-3). Raninoides rioturbiensis has a longer intraorbital spine narrowing to the front and the base of the anterolateral spine is smaller (Schweitzer etal. 2012: fig. 4). Raninoides sinuosus exhibits a smaller base of the anterolateral spine and sternite 4 is proportionally shorter (Collins & Morris 1978: pl. 116.4-6). Raninoides slaki has a bifid intra-orbital spine and the maximum carapace width is located further posteriorly (Squires 2001: figs 47-55). Raninoides treldenaesensis bears a smaller anterolateral spine and sternite 4 is proportionally shorter (Collins & Jakobsen 2003: fig. 4, pl. 3.5). Raninoides vaderensis appears close but its anterolateral spine is oriented more forwardly (Rathbun 1926: pl. 22.5; Tucker 1998: fig. 17; Gustafson 2023: figs 16-19). Raninoides washburnei has a more forwardly oriented anterolateral spine and its carapace is proportionally wider (Rathbun 1926: pl. 22.6). We did not compare the new species to post-Eocene species because brachyuran species ranging for >32 million years are extremely unlikely and unknown to us. Section EUBRACHYURA de Saint Laurent, 1980 Subsection HETEROTREMATA Guinot, 1977 Superfamily retroplumoidea Gill, 1894 Family retroplumidae Gill, 1894 Genus Costacopluma Collins & Morris, 1975 type speCies. — Costacopluma concava Collins & Morris, 1975, by original designation. iNCluded speCies. — Costacopluma australis Feldmann, Casadío, Chirino-Gálvez & Aguirre-Urreta, 1995; C. bifida Collins, Higgs & Cortitula, 1994; C. bishopi Vega & Feldmann, 1992; C.binodosa Collins & Wienberg Rasmussen, 1992; C. concava Collins & Morris, 1975; C. grayi Feldmann & Portell, 2007; C.maroccana OssóMorales, Artal & Vega, 2010; C. mexicana Vega-Vera & Perrilliat, 1989; C. mamethioupamei Hyžný, Perrier, Robin, Martin & Sarr, 2016; C.nicksabani n. sp.; C. nordestina Feldmann & Martins-Neto, 1995; C. salamanca Feldmann, Rodriguez, Martinez & AguirreUrreta, 1997; C. squiresi Nyborg, Vega & Filkorn, 2023; C.texana Armstrong, Nyborg, Bishop, Ossó-Morales & Vega, 2009; C. senegalensis (Rémy in Gorodiski & Rémy, 1959). diagNosis. — Small rectangular to ovoid carapace, wider than long; carapace surface distinctly flattened and traversed by three elevated, granular ridges, the anteriormost being complete and often biconvex forwards; posterior two ridges converging axially defining depressed, triangular to rectilinear, smooth mesobranchial region. Rostrum generally narrow, downturned, bilobed. Carapace flanks distinct, 597 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) about perpendicular to dorsal surface and separated from it by beaded rim. Sternum broad, with well-defined sternites; sternites 5-7 each with prominent transverse, beaded ridge; male sternopleonal cavity deep, reaching end of sternite 4. Transverse ridges also present on pleonal somites. Pereiopod 5 subdorsal, reduced. Emended from Feldmann etal. (2014: 137). fig. 13. — Raninoides danicus n. sp. from the lower Danian Pine Barren Member (Clayton Formation) found at the roadcut of Mussel Creek, Lowndes County, Alabama: A, ventral view of MMNS IP-8792; B, dorsal view of MMNS IP-7252.1; C, dorsal view of MMNS IP-7253.1; D, right posterolateral view of holotype ALMNH:Paleo:21488; E, ventral view focused on sternites 3-4 of paratype ALMNH:Paleo:21490; F, left posterolateral view of paratype ALMNH:Paleo:21489; G, frontal view of sternite 3 of paratype ALMNH:Paleo:21490. Scale bars: 5.0 mm. Credits: photos by Adiël A. Klompmaker. AB C D E F G 598 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. Costacopluma grayi Feldmann & Portell, 2007 (Figs 14; 15; Table 1; Appendix 1F) Costacopluma grayi Feldmann & Portell, 2007: 92, figs 2, 3. — Armstrong etal. 2009: fig. 6.2-6.3. — Martínez-Díaz etal. 2016: fig. 5.9-5.10. non Costacopluma grayi – Feldmann etal. 2014: 137, pls 1, 2. (Costacopluma nicksabani n. sp.). — Martínez-Díaz etal. 2016: figs 5.15.8; 6.4. (Costacopluma nicksabani n. sp.). — Martínez-Díaz etal. 2016: figs 4; 6.4. — Vega etal. 2016: fig. 4G, H. t ype material . — Holotype. United States • 1 specimen; Alabama, Covington County, Below Point A Dam (31°21’32”N, 86°31’11”W), ALMNH loc. 4; Tallahatta Formation, NP14 nannofossil zone; Eocene (upper Ypresianlower Lutetian); UF 113749. Paratypes. United States • 1 specimen; same as for the holotype; UF 113748 • 1 specimen; idem; UF 113750 • 1 specimen; idem; UF 114747 • 1 specimen; idem; UF 115672 • 1 specimen; idem; UF 115793 • 1 specimen; idem; UF 115794 • 1 specimen; idem; UF 115795 • 1 specimen; idem; UF 115796. additioNal material examiNed. — United States • 2 specimens; Alabama, Covington County, Below Point A Dam (31°21’32”N, 86°31’11”W), ALMNH loc. 4; Tallahatta Formation, NP14 nannofossil zone; Eocene (upper Ypresianlower Lutetian); ALMNH:Paleo:20598 • 1 specimen; idem; ALMNH:Paleo:21440 • 3 specimens; idem; MMNS IP-6491 • 1 specimen; idem; MMNS IP-6492 • 2 specimens; idem; MMNS IP-10046 • 1 specimen; idem; MMNS IP-11213 • 1 specimen; idem; UF 116615 • 1 specimen; idem; UF 116619 • 1 specimen; idem; UF 142615 • 1 specimen; idem; UF 142616 • 1 specimen; idem; UF 116691 • 1 specimen; idem; UF 171033 • 1 specimen; idem; UF 171034 • 1 specimen; idem; UF 256410 • 1 specimen; Alabama, Conecuh County, Pigeon Creek (T5N, R14E, Sec. 20, NE¼, NE¼); Tallahatta Formation, NP14 nannofossil zone; Eocene (upper Ypresianlower Lutetian); UF 287265 • 1 specimen; idem; UF 287266 • 1 specimen; idem; UF 349284-349310. type horizoN. — Tallahatta Formation, NP14 nannofossil zone, Eocene (upper Ypresianlower Lutetian). type loCality. — Below Point A Dam (31°21’32”N, 86°31’11”W), Covington County, Alabama, United States. A B C D EF GH fig. 14. — Costacopluma grayi Feldmann & Portell, 2007, from the Eocene (upper Ypresian-lower Lutetian) Tallahatta Formation in Alabama: A-C, dorsal views of ALMNH:Paleo:20598B, MMNS IP-10046.1, and MMNS IP-11213; D, right propodus and dactylus of UF 287266; E, F, frontal views of UF 171033 and ALMNH:Paleo:20598B; G, H, ventral views including male pleon of MMNS IP-11213. Scale bars: 5.0 mm. Credits: photos by Adiël A. Klompmaker. 599 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) d iagNosis . — Carapace relatively small (<15 mm maximum width), subrectangular, wider than long (l/w ratio c. 0.9), widest point posterior to mid-length. Fronto-orbital margin c. 70% of maximum width; lateral margins somewhat diverging posteriorly, fairly straight, but more convex posteriorly; posterior margin nearly straight. Rostrum inclined downward, slightly longer than wide, minimum width in dorsal view c. 4% of maximum carapace width. Outer orbital spine small, triangular, directed forward. Dorsal carapace containing three tubercular transverse ridges of narrow width on average, with rounded tops; anterior ridge sinuous, uninterrupted, diminishes toward but reaches lateral margins. Cardiac region raised, tubercular, with convex and flattened ridge anteriorly and raised extension axially directed posteriorly. Gentle swellings with tubercles just anterior to innermost part of posterolateral margins. measuremeNts. — See Table 1. desCriptioN Referral is made to Feldmann & Portell (2007: 92). Additional specimens allow for improved description of rostrum, outer orbital spine, posterior margin, cheliped, sternum, and pleon. Outer orbital spine small, appears directed forward (UF 115796). Partial rostrum narrow, minimally c.4% of maximum carapace width in dorsal view. Posterior margin with one row of small tubercles on top of rim, curving somewhat forward in lateral parts, nearly straight to very slightly concave in axial part (MMNS IP-11213, UF 171033). Outer side propodus (UF 287266) without tubercles as preserved, with a groove near base extending onto fixed finger, with at least four pits on fixed finger close to occlusal surface. Male sternite 4 with distinct, tubercular rim on outer side; less distinct rim on inner side, marking deep sternopleonal cavity for telson; generally smooth on cuticular surface in between. Somites male pleon unfused, with transverse, tubercular keels; telson with rounded tip. remarks Several papers ascribed early Danian and Maastrichtian specimens to this species (Feldmann etal. 2014; Vega etal. 2016; Martínez-Díaz etal. 2016), but there are several morphological differences between the specimens from the Eocene and these c.18-19 million years older specimens that warrant species-level separation. For the early Danian specimens, referral is made to the new species erected below. The Maastrichtian specimens also represent a different species of Costacopluma not treated further herein: they have an outer orbital spine directed anterolaterally instead of forward as in C. grayi (UF 115796), are proportionally wider, and have a greater maximum size (see Vega etal. 2016; Martínez-Díaz etal. 2016). Specimens with light to dark brown cuticle are embedded in tan/light brown fine sediment with some sand. Others occur in tan-brown sediment with more sand embedded, and a very dark brown cuticle. Finally, some occur in dark gray sediment and have dark brown cuticle. This applies to specimens from Point A Dam and Pigeon Creek. Some are listed as found insitu (UF 116615, UF 116619, UF 116691) or found in bed 5 of Copeland (1966) (UF 171033, UF 171034, type series), but the preservation style differs. It is likely that specimens underwent somewhat different taphonomic histories. Some specimens (MMNS IP-11213 and MMNS IP-10046) are listed to have come from the basal Lisbon Formation in “Bed 5” of Copeland (1966), which Feldmann & Portell (2007) interpreted to be the Tallahatta Formation (see also Savrda etal. 2010). Additional specimens were briefly mentioned in a paper focused on the vertebrate fauna of Point A Dam (Clayton etal. 2013). Unfortunately, the whereabouts of those crabs is uncertain (pers. comm. AAK with the Chuck Ciampaglio, November 2023). Costacopluma texana Armstrong, Nyborg, Bishop, Ossó-Morales & Vega, 2009 (Fig. 16; Table 1; Appendix 1G, H) Costacopluma texana Armstrong, Nyborg, Bishop, Ossó-Morales & Vega, 2009: 756, figs 5.14-5.20; 6.1. — Martínez-Díaz etal. 2016: figs 5.14, 6.6. type material. — Holotype. United States • 1 specimen; Texas, Limestone County, quarry c. 2 miles west of Mexia (c. 31°40’12”N, fig. 15. — Carapace ratios of Costacopluma spp. versus specimen size: A, length-width ratios; B, rostral width-maximum carapace width ratios. See Table 1 for measurements. 0.12 0.11 0.10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 6.07.0 8.09.0 10.0 11.0 12.0 13.0 14.0 1.00 0.98 0.96 0.94 0.92 0.90 0.88 0.86 0.84 6.07.0 8.09.0 10.0 11.0 12.0 13.0 14.0 AB Maximum carapace width ( mm )Maximum carapace width ( mm ) Rostral width-maximum width ratio Lenght-width ratio Costacopluma grayi (early Eocene) C. nicksabani n. sp. (early Danian) C. texana (late Danian) Costacopluma grayi (early Eocene) C. nicksabani n. sp. (early Danian) C. texana (late Danian) 606 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. has a significantly higher length-width ratio (Mann-Whitney p = 0.0005; Figs 15-18; Table 1), appears to exhibit a thicker upper orbital rim (Fig. 15G, I vs Fig. 16D, G; 17B), has an oval-shaped oviduct rather than subcircular in C. nicksabani n. sp. (Fig. 16K vs Fig. 17M), the transverse ridges on sternites 5-6 are taller in at least females, the outer lateral margins of sternite 4 appear more flared up on average, and the press button on males is larger (Fig. 16L vs Fig. 18N). We did not observe obvious ontogenetic variation, perhaps because of the limited size range of specimens. Sexual dimorphism is not observed on the dorsal carapace, but it is evident on the ventral side (wider female pleon and other characters, see description). Intraspecific variation is limited despite the high number of specimens. For lesser preserved specimens with cuticle, the tubercles on the transverse ridges are less obvious. Carapace ornamentation is difficult to discern on internal molds (ALMNH:Paleo:21497A, 1 specimen of UF 235569). The sediment surrounding Mussel Creek specimens varies from tan to dark gray and from friable to fully lithified. This observation may indicate differing taphonomic conditions. The gonopods preserved in three specimens of Costacopluma nicksabani n. sp. (ALMNH:Paleo:21457, MMNS IP-7940.1, UF 303806; Fig. 16I, M) resemble those in extant retroplumids (de Saint Laurent 1989). The preservation of gonopods in fossil brachyurans is uncommon (e.g., Karasawa & Schweitzer 2006: 42; Garassino etal. 2013: 356), and they had not been recognized within Costacopluma and fossil Retroplumidae until this paper. These small pleonal appendages, often taxonomically important for extant crabs, are less calcified than walking appendages and claws and tend to be covered by the pleon within the sternopleonal cavity. Fossil brachyuran species with these structures have been more frequently recognized over the last decade, mostly in specimens that have the pleonal somites incompletely preserved exposing structures underneath (Smirnov 1929; Secrétan 1975; Karasawa & Kato 2001, 2019; Guinot & Breton 2006; Karasawa & Schweitzer 2006; Artal etal. 2008; Feldmann etal. 2011; Schweitzer & Feldmann 2015; Luque etal. 2018, 2019; Pereyra etal. 2019; Lima etal. 2020; Pereyra & Verde 2020; Hyžný etal. 2022; Kovalchuk etal. 2023). The preservation of delicate tips of gonopods herein is even rarer. Superfamily Carpilioidea Ortmann, 1893 Family palaeoxaNthopsidae Schweitzer, 2003 Palaeoxanthopsidae indet. (Fig. 19) material examiNed. — United States • 1 specimen; Alabama, Lowndes County, Mussel Creek roadcut (31°58’17”N, 86°42’15”W), ALMNH loc. 3; Clayton Formation, Pine Barren Member, lower middle NP2 nannofossil zone; Paleocene (lower Danian); ALMNH:Paleo:21482 (carapace) • 51 specimens; idem; ALMNH:Paleo:21497 (51 carapaces/venters) • 1 specimen; idem; ALMNH:Paleo:21505 (fixed finger) • 2 specimens; idem; ALMNH:Paleo:21506 (fixed fingers) • 1 specimen; idem; MMNS IP-7256.1 (fixed finger) • 1 specimen; idem; UF 303867 (fixed finger) • 1 specimen; idem; UF 303870 (fixed finger) • 1 specimen; idem; ALMNH:Paleo:21507 (dactylus) • 4 specimens; idem; ALMNH:Paleo:21508 (dactyli) • 1 specimen; idem; MMNS IP-7256.2 (dactylus) • 1 specimen; idem; UF 303868 (dactylus) • 1 specimen; idem; UF 303869 (dactylus) • 1 specimen; idem; UF 303871 (dactylus) • 1 specimen; idem; UF 303872 (dactylus). measuremeNts. — Maximum carapace width (mm): ALMNH:Paleo:21482: 24.6 desCriptioN Preserved carapace c.24.6 mm wide without anterolateral projections, weakly vaulted transversely, moderately vaulted longitudinally. Fronto-orbital width c.55% of maximum width. Anterolateral margin with bases of four projections. Carapace with five large protuberances, one marking base of mesogastric region, two adjacent to anterior part of mesogastric region, and two lateral to cervical groove at level of mesogastric region base. Transverse row of small bumps anterolaterally of posteriormost set of protuberances. On cuticle, tubercles on protuberances and in front of anteriormost protuberances. Pit present in front of each side of posterior part of mesogastric region. Flanks steep. Preserved pterygostome appears subtriangular. Sternite 3 wider than long, separated from sternite 4 by a concave groove. Sternite 4 intersected by narrow sternopleonal cavity, both sides appear square-shaped. Coxa and basis of pereiopod 1, and parts of maxilliped 3 preserved. Sternum and appendages covered by tubercles, except for grooves and sternopleonal cavity. Rostrum, posterior carapace, most of ventral side, pleon, and appendages missing. Fixed finger robust; curved inward; with row of oval tubercles, variably sized, diminishing in size to tip on average; outer and inner lateral sides with row of pits. Dactylus curved; with strong tubercle on outer side of occlusal surface near base, followed by smaller, similar-sized tubercles toward tip. remarks The single carapace lacks the posterior portion, the frontal region including the orbital structure and the rostrum, and the projections on the anterolateral margins. The preserved characters fit those of Palaeoxanthopsidae (e.g., Schweitzer 2003; Schweitzer etal. 2018a, 2025; Vega etal. 2018), includ - ing the location of the spherical swellings on the carapace and the anterolateral margins with bases of projections. Specimens of the Maastrichtian genera Palaeoxanthopsis Beurlen, 1958, and Parazanthopsis Vega, Feldmann, García-Barrera, Filkorn, Pimentel & Avendano, 2001, are morphologically close to the single, incomplete carapace specimen herein. The collection of more complete carapaces is necessary for identification beyond the family level. We also found various fingers attributable to Palaeoxanthop - sidae. Both fixed fingers and dactyli conform well to those seen in Palaeoxanthopsidae such as Paraverrucoides alabamensis (Rathbun, 1935a) from the upper Danian Porters Creek Formation of Alabama (GSA-I21006 and GSA-I21010) and Lobulata lobulata (Feldmann, Casadio, Chirino-Galvez & Aguirre-Urreta, 1995), from the Maastrichtian-Danian of 607 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) Argentina (their fig. 7.6). It is very likely that these isolated fingers belong to the same species as the carapace, but associated chelipeds with a carapace are needed for verification. Superfamily hexapodoidea Miers, 1886 Family hexapodidae Miers, 1886 iNCluded geNera. — Bellhexapus De Angeli, Guinot & Garassino, 2010; Eohexapus De Angeli, Guinot & Garassino, 2010; Eurohexapus De Angeli, Guinot & Garassino, 2010; Goniocypoda Woodward, 1867; Headonipus Quayle & Collins, 2012; Hexalaughlia Guinot, 2006; Hexapinus Manning & Holthuis, 1981; Hexaplax Doflein, 1904; Hexapus De Haan, 1835 [in 1833-1850]; Holthuisea Guinot, De Angeli & Garassino, 2010; Lambdophallus Alcock, 1900; Latohexapus Huang, Hsueh & Ng, 2002; Lucahexapus De Angeli & Caporiondo, 2022; Mariaplax Rahayu & Ng, 2014; Paeduma Rathbun, 1897; Palaeopinnixa Vía, 1966; Parahexapus Balss, 1922; Pseudohexapus Monod, 1956; Rayapinus Rahayu & Ng, 2014; Rodneyellus Lima, Alcântara, Aguilera & Tavares, 2025; Spiroplax Manning & Holthuis, 1981; Stevea Manning & Holthuis, 1981; Thaumastoplax Miers, 1881; Theoxapus Rahayu & Ng, 2014; Tritoplax Manning & Holthuis, 1981. fig. 19. — Palaeoxanthopsidae indet. from the lower Danian Pine Barren Member (Clayton Formation) found at the roadcut of Mussel Creek, Lowndes County, Alabama: A-D, dorsal, right lateral, frontal, and ventral views of ALMNH:Paleo:21482; E-H, outer, inner, lower marginal, and occlusal views of fixed finger of UF 303867; I-L, outer, inner, upper marginal, and occlusal views of dactylus of ALMNH:Paleo:21507. Scale bars: A-D, 10.0 mm; E-L, 5.0 mm. Credits: photos by Adiël A. Klompmaker. AB C D E FGH IJKL 608 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. Genus Alahexapus n. gen. urn:lsid:zoobank.org:act:C230B4E9-59C4-4322-9057-5513F4722A93 type speCies. — Stevea martini Feldmann, Schweitzer & Portell, 2014, by present designation. etymology. — Alarefers to Alabama and -hexapus refers to the type genus of Hexapodidae. Gender: masculine. diagNosis. — As for the type species. remarks Stevea martini was ascribed to Stevea based on a limited number of specimens then available without male and female pleons. Two additional specimens collected since 2014 with male and female pleons preserved suggest assignment to this genus is not tenable. Specifically, the female pleon from the only specimen of Stevea williamsi, the type and sole extant species of Stevea, was demonstrated to be narrow and have somites 2-6 fused (Guinot etal. 2010), whereas the female individual of Alahexapus martini n. comb. has proportionally wider pleonal somites 4-6 and these somites are unfused. Additional differences include the anterolateral borders passing below the outer orbital angle rather than joining the outer orbital angle as in A. martini n. comb., the rostrum has a concave border rather than a straight border as in A. martini n. comb., and the rostrum is widening distally rather than being straight laterally (UF 254042). The degree of fusion of pleonal somites and the pleonal width are considered important characters distinguishing between genera among extant hexapodids (Rahayu & Ng 2014). Other characters frequently used in that paper for genus diagnoses are carapace length-width ratios, cuticle ornamentation, groove development on the carapace, anterolateral margin shape, eye size, maxilliped morphology, ornamentation including stridulatory striae on the pterygostome, cheliped morphology, the degree of sternite and somite fusion, the shape of the pleon, and the shape and reach of the sternopleonal cavity. Many of the same characters are used to define genera present in the fossil record when preserved, but also other characters related to the carapace have been used including the widest point of the carapace, the frontal margin morphology and relative dimensions, and the orbital cavity size and shape (e.g., De Angeli etal. 2010; Schweitzer etal. 2022). Key differences between Alahexapus n. gen. and exclusively fossil genera exist. Bellhexapus is widest at the posterior margin, male somite 6 is longer, and male somites 3-5 are not fused (De Angeli etal. 2010: figs 2, 3). In Eohexapus, the orbits are circular rather than oval and the dorsal carapace is smooth rather than showing some grooves (De Angeli etal. 2010: figs 4-6). Eurohexapus exhibits a carapace about as long as wide rather than wider than long, its fronto-orbital width is greater (c.65% of maximum width vs 50% for Alahexapus n. gen.), and male somites 2-6 are fused (De Angeli etal. 2010: figs 7-9). Goniocypoda has a relatively wide fronto-orbital width (c.65% of maximum width vs c.50% for Alahexapus n. gen.) (Schweitzer & Feldmann 2001: 335). For Headonipus, the “grooves curving from the base of the cardiac region to the middle of the coxigeal incisions isolate elongated intestinal lobes” (Quayle & Collins 2012: 40), are not observed in Alahexapus n. gen. Moreover, the posteriormost portion of the carapace of Headonipus appears much more depressed and the orbits are subcircular rather than oval (Quayle & Collins 2012: pl. 3.9-3.10; Schweitzer etal. 2022: fig. 7.5). For Holthuisea, carapace grooves are absent and male somites 3-6 are fused rather than somites 3-5 only (Guinot etal. 2010: figs 2-4). Lucahexapus has a proportionally greater fronto-orbital width (c.67% of maximum carapace width vs c.50%) and the cervical groove is much wider (De Angeli & Caporiondo 2022: figs 2.5, 3.5). For Palaeopinnixa, the carapace is widest just anterior to posterolateral reentrants (e.g., Hyžný & Artal 2018; Schweitzer etal. 2022; Gustafson 2023), but Alahexapus n. gen. is widest about mid-length and does not widen toward the posterior carapace. Moreover, somites 5-6 in females are fused for the type species P. rathbunae and this species does not exhibit stridulating apparatus/striae on the pterygostome (Schweitzer etal. 2000: 57). Rodneyellus lacks a U-shaped cervical groove and has a lower ratio of fronto-orbital width of maximum carapace width (0.37 vs 0.50). Key differences also exist with extant genera other than Stevea as discussed above, primarily using diagnoses in Manning & Holthuis (1981), Guinot (2006), and Rahayu & Ng (2014). Hexalaughlia exhibits a pterygostome without a row of stridulatory striae, and male somite 6 is much longer. Hexapinus has a carapace widening posteriorly, the carapace regions are not demarcated except for a poorly defined cardiac region, the orbits are much smaller, and male somite 6 is longer. For Hexaplax, the carapace regions are more indistinct, the orbits are larger and are subcircular rather than oval. For Hexapus, the carapace regions are less distinct, and the orbits are much smaller. Lambdophallus bears much smaller orbits and exhibits a male transverse sternal groove extending laterally from the sternopleonal cavity not seen in Alahexapus n. gen. Latohexapus has much more distinct carapace regions and its carapace widens posteriorly. Mariaplax has a carapace widening posteriorly, smaller orbits, and a much shorter male telson. Paeduma exhibits a much longer male somite 6 and carapace grooves are absent to very faint. Parahexapus bears a much longer male somite 6 that is narrower than male somites 3-5, and has orbits that are smaller. For Pseudohexapus, the pterygostome lacks a row of oblique striae. Rayapinus has a carapace without clear grooves, bears a relatively narrow female pleon, has female somites 1-5 fused, and has a male telson almost as long as somite 6. Spiroplax exhibits a carapace that is widening posteriorly, and has a much broader male pleon with a triangular telson. For Thaumastoplax, the pterygostome lacks a row of oblique striae, the orbits are smaller and circular, and the carapace regions are indistinct. Theoxapus has much smaller orbits and a proportionally longer male somite 6. Tritoplax has a male telson with a triangular tip, a male pleonal somite 6 that is divided longitudinally, and apparently smaller orbits. As none of the diagnoses of fossil and extant genera match the species under study, we erect Alahexapus n. gen. It is possible additional fossil species may belong to the new genus. 609 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) For example, Palaeopinnixa rocaensis (Feldmann, Casadío, Chirino-Gálvez & Aguirre-Urreta, 1995), from the Danian of southern Argentina does not widen toward to posterior carapace as for the genus diagnosis of Palaeopinnixa ( Schweitzer & Feldmann 2001). The fronto-orbital width is similar (45% of maximum width vs c.50% for Alahexapus n. gen.), the outline is similar, the flanks for both taxa are straight, the length-width ratio is similar (0.71 vs c.0.67 for Alahexapus n. gen.) (Feldmann etal. 1995: figs 14, 15). Unfortunately, no cuticle is preserved nor any ventral characters, which hinders further evaluation. Alahexapus martini (Feldmann, Schweitzer & Portell, 2014) n. comb. (Fig. 20; Appendix 1K, L) Stevea martini Feldmann, Schweitzer & Portell, 2014: 142, pl. 3. t ype material . — Holotype. United States • 1 specimen; Alabama, Lowndes County, Mussel Creek roadcut (31°58’17”N, 86°42’15”W), ALMNH loc. 3; Clayton Formation, Pine Barren Member, lower middle NP2 nannofossil zone; Paleocene (lower Danian); UF 228988. Paratype. United States • 1 specimen; same as for the holotype; UF 235561. additioNal material examiNed. — United States • 1 specimen; Alabama, Lowndes County, Mussel Creek roadcut (31°58’17”N, 86°42’15”W), ALMNH loc. 3; Clayton Formation, Pine Barren Member, lower middle NP2 nannofossil zone; Paleocene (lower Danian); ALMNH:Paleo:5915 • 1 specimen; idem; ALMNH:Paleo:21464 • 1 specimen; idem; MMNS IP-7939 • 1 specimen; idem; UF 254040 • 1 specimen; idem; UF 254041 • 1 specimen; idem; UF 254042 • 1 specimen; idem; UF 303801. type horizoN. — Pine Barren Member of the Clayton Formation, lower middle NP2 nannofossil zone, lower Danian. type loCality. — ALMNH loc. 3: Mussel Creek roadcut (31°58’17”N, 86°42’15”W), Lowndes County, Alabama, United States. diagNosis. — Carapace length-width ratio c. 0.67, widest about mid-length. Fronto-orbital width c. 50% of maximum carapace width. Orbits of moderate size, oval-shaped. Cervical groove widely U-shaped but diverging, fairly distinct, diminishing near orbits. Branchiocardiac grooves weaker, defining cardiac region laterally. Cuticle of carapace with densely covered fine granules. Pterygostome exhibiting stridulating apparatus with c. 15 striae. Female pleon with unfused, much wider than long somites; triangular telson with rounded tip; with gentle axial keel; pitted cuticular surface. Sternopleonal cavity of female appears to reach distal portion of sternite 3. Male pleon narrow, generally narrowing distally; telson longer than wide with rounded tip; somite 6 slightly wider than long, appears unfused, hexagonal, with rimmed lateral margins; somites 3-5 appear fused but with distinct suture marking boundaries; with pitted cuticular surface. Sternopleonal cavity of male appears to reach distal portion of sternite 4. measuremeNts. — Maximum carapace width (mm): ALMNH:Paleo:5915: 7.1, ALMNH:Paleo:21464: 11.1. UF 228988: 11.1, UF 254041: 8.9, MMNS IP-7939: 11.4. desCriptioN Referral is made to Feldmann etal. (2014: 142-143). Some additional and revised characters are noted in new specimens. Carapace length-width ratio c.0.67. Fronto-orbital width c.50% of maximum carapace width. Sternites with tubercular and pitted cuticular surface; pleonal sternite 2 narrow; sternites 3-4 fused; sternite 4 with curved, anterolaterally directed spine separated by sulcus. Female pleon with unfused, much wider than long somites; triangular telson with rounded tip; maximum width pleon c.30% of maximum carapace width; with gentle axial keel; pitted cuticular surface. Female pleonal somites 1-3 not preserved. Sternopleonal cavity of female appears to reach distal portion of sternite 3; with small press button on sternite 5 on upper part of slope near sternite 4; with subcircular oviduct on sternite 6, adjacent to base of sternopleonal cavity. Male pleon narrow, generally narrowing distally; telson longer than wide with rounded tip; somite 6 slightly wider than long, appears unfused, hexagonal, with rimmed lateral margins; somites 3-5 appear fused but with distinct line marking boundaries; with pitted cuticular surface. Sternopleonal cavity of male appears to reach distal portion of sternite 4. Third maxilliped partly preserved, with elongated exopod; boot-shaped, tubercular ischium, and about equally wide and long, rounded merus. Appendages not preserved. remarks This species is rare with only nine individuals reported herein after c.15 years of collecting. This rarity is not primarily caused by the small size of the specimens, making them potentially more difficult to find, because many small specimens of other species were found (see above). Recently, Schweitzer (2024) ascribed four specimens to Stevea martini from a site near Streetman, Freestone County, Texas, United States, originating from the upper Danian-Selandian Wills Point Formation (see Armstrong etal. 2009, for age). However, the tubercles on the dorsal carapace are coarser on average and more uniform in the Texan specimens based on all available specimens; sternite 4 has a wider, hexagonal-shaped extension as preserved rather than anterolaterally directed, curved spines as in A. martini n. comb. (compare Schweitzer 2024: fig. 3.2 vs Fig. 20E); and the pterygostome does not appear to bear the stridulating apparatus (Schweitzer 2024: fig. 3.6) characteristic for A. martini n. comb. (Fig. 20L; Feldmann etal. 2014: pl. 3.2) though differential preservation may play a role here. Thus, the specimens from Texas may represent a different hexapodid species warranting further study. DISCUSSION biostratigraphy aNd age The lithostratigraphic section analyzed in this study belongs to calcareous nannofossil Zone NP2. The base of NP2 occurs c.2.75 m below the base of the section shown in Figure 2, with the first occurrence/base of Cruciplacolithus intermedius (and other bioevents such as the first occurrences of Coccolithus pelagicus (Wallich, 1877) and Futyania spp. [super-abundant]). A numeric age of 65.50 Ma is assigned to the base of NP2, following the global ages from Gradstein etal. (2012). The section has been subdivided into lower-middle-upper NP2 610 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. fig. 20 . — Alahexapus martini (Feldmann, Schweitzer & Portell, 2014) n. comb. from the lower Danian Pine Barren Member (Clayton Formation) found at the roadcut of Mussel Creek, Lowndes County, Alabama: A-C, dorsal, frontal, left lateral views of ALMNH:Paleo:5915; D-F, frontal, partial ventral, and dorsal views of UF 254041; G, ventral view of MMNS IP-7939 with female pleon; H, ventral view of ALMNH:Paleo:21464; I, closeup of maxilliped 3 of MMNS IP-7939; J, K, ventral views of UF 254040 with male pleon; L, view of partially preserved stridulating apparatus (vertical ridges arranged diagonally) of MMNS IP-7939; M, dorsal view of ALMNH:Paleo:21464. Scale bars: 2.0 mm. Credits: photos by Adiël A. Klompmaker. AB C D E F GH I J K L M 611 Early Danian decapods from Alabama, United States GEODIVERSITAS • 2025 • 47 (13) based on the identification of biostratigraphically useful nannofossil-events used in the zonation schemes of Varol (1989) and Bown etal. (2023). The deepest sample analyzed in this study belongs to lower NP2, with the first occurrence/ base of Praeprinsius tenuiculus (Okada & Thierstein, 1979) (Fig. 2). The middle NP2 is based on the last occurrence/top of Futyania spp. [super-abundant], whereas upper NP2 is defined by the first occurrence/base of Praeprinsius dimorphosus (Perch-Nielsen, 1977) [common/increase] (Fig. 2). The base of NP3 (64.81 Ma, Gradstein etal. 2012) was not observed, as the uppermost sample analyzed is within upper NP2. The lower middle NP2 nannofossil zone assigned to nearly all decapods and other fossils from the Mussel Creek outcrop, allows us to evaluate the absolute age of the assemblage. Using the astronomically calibrated NP zonation of Hvid etal. (2021: fig. 12) and an age model coupled with the NP zonation in Bown etal. (2023), we infer an absolute age of 65.465.3 Ma for the assemblage. This inference implies the fauna lived c.600-700k years after the K-Pg boundary (66.0 Ma). stratigraphiC aNd paleobiogeographiC impliCatioNs of the deCapod assemblage Raninoides danicus n. sp. is the stratigraphically second to oldest species known of the genus after R. granulofrons, from the late Campanian-early Maastrichtian of Cuba. This genus has not been reported previously from the fossil record of the southeastern United States. Eucalliaxiopsis alabamensis n. comb., Ctenocheles sp., and Palaeoxanthopsidae were unknown from the early Danian of Alabama thus far, but they have been reported from the upper Danian Porters Creek Formation of the state (Rathbun, 1935a). deCapod paleoeCology All decapods appear to have lived in or on the bottom of the muddy substrate. At least one decapod taxon in our assemblage was a likely durophagous predator. Multiple species of Palaeoxanthopsidae, such as Paraverrucoides alabamensis, Lobulata lobulata, and the indeterminate species in the Mussel Creek assemblage, bear molariform teeth on the fixed finger and a large tooth projecting inward on the dactylus, located more on the outer than inner side of the occlusal surface. This tooth is reminiscent of the more curved and larger tooth that calappid crabs use to break shells (Shoup 1968). Such characters have been ascribed to shell-preying crabs (Schweitzer & Feldmann 2010); thus, we suggest Palaeoxanthopsidae were likely molluscan predators. Mollusks are common at Mussel Creek (Figs 3; 4). The three axiidean species were burrowers (e.g., Hyžný & Klompmaker 2015: table 1), and burrows are commonly found at the Mussel Creek roadcut. As extant hexapodids have been found in burrows (Rahayu & Ng 2014; Naruse 2020), Alahexapus martini n. comb. may have had a similar lifestyle. As for extant retroplumids (de Saint Laurent 1989), Costacopluma nicksabani n. sp. likely lived on the muddy bottom or burrowed, feeding on organic particles within the sediment. As for nearly all Cenozoic paguroids (e.g., Fraaije & Polkowsky 2016; Pasini etal. 2020), specimens of “Paguristes” johnsoni likely relied on gastropod shells as a domicile, which were common at Mussel Creek (Fig. 4). The carapace shape of Raninoides danicus n. sp. suggests it was likely burying in the sediment (e.g., Van Bakel etal. 2012). Little is known about the diet of raninoidans, but Ranina ranina Linnaeus, 1758, appears to be a scavenger (Baylon & Tito 2012). Evidence of preserved predation inflicted on decapods is generally rare in the fossil record (Klompmaker etal. 2013, for a summary). One of the Raninoides danicus n. sp. specimens (MMNS IP-7252.2) figured in Feldmann etal. (2019: fig. 5B) bears two elongated depressions diagonally across the carapace. All cuticle is present within these depressions and there is no sign of a tooth impression. They were unsure but suggested biting or crushing by a predator as one explanation. These traces do not match known traces attributed to predation in fossil decapods. We, too, are unsure about the cause. table 2. — Number of specimens per taxon. Carapaces and isolated appendage elements are all counted as one individual. Taxon Total # specimens Carapaces/venters with or without appendages Propodi with or without dactylus Fixed fingers Fixed finger and associated dactylus Dactyli Meri Cheliped Finger indet. Alphacheles zeta (Rathbun, 1936) n. comb. 6 – 6 – – – – – – Ctenocheles sp. 1 – – – – – – – 1 Eucalliaxiopsis alabamensis (Rathbun, 1935) n. comb. 111 – 1 31 2 76 – 1 – “Paguristes” johnsoni Rathbun, 1935 7 – 1 – 1 4 1 – – Raninoides danicus n. sp. 20 20 – – – – – – – Costacopluma nicksabani n. sp. 183 174 5 1 – – 2 1 – Palaeoxanthopsidae indet. 17 1 – 6 – 10 – – – Alahexapus martini (Feldmann, Schweitzer & Portell, 2014) n. comb. 9 9 – – – – – – – 612 GEODIVERSITAS • 2025 • 47 (13) Klompmaker A. A. et al. None of the specimens studied show evidence of Kanthyloma crusta Klompmaker, Artal, Van Bakel, Fraaije & Jagt, 2014, the trace fossil attributed to parasitism in the branchial chamber by an epicaridean isopod (see also Klompmaker etal. 2022b). Thus, levels of this type of parasitism were low. diversity of early daNiaN deCapod assemblages All to nearly all decapod species of the early Danian Mussel Creek assemblage have been collected as suggested by a rarefaction analysis (Fig. 21; Table 2). The eight species recognized herein make it one of the most diverse early Danian assemblages known relatively soon after the Cretaceous-Paleogene mass extinction. This is partly because of the lack of studies on such assemblages, but also because biostratigraphic data is not always available to place assemblages within a part of the Danian (e.g., Feldmann etal. 1993; Robin etal. 2017). From the lower Danian Roca Formation at Cerros Bayos in southern Argentina (NP1 nannofossil zone), five decapod species were reported (Feldmann etal. 1995). They also reported one species from the early Danian General Roca outcrop, but eight other species came north from there, implying the precise age within the Danian is uncertain. From the early Danian Clayton Formation in Illinois, United States, four species were reported (Cope etal. 2005). Finally, Jensen (2013) informally reported on an early Danian assemblage from Sangstrup in Denmark, consisting of 15 species. Although a more thorough study on Sangstrup material is ongoing, alpha diversity appears to be higher than in the assemblage of Mussel Creek. Acknowledgements Austin Hendy and Juliet Hook (both Natural History Museum of Los Angeles County, California, United States) are thanked for a loan of specimens ascribed to Costacopluma squiresi and Torrey Nyborg (Loma Linda University, California, United States) for photos of this species as well as photos of C. texana. Liath Appleton (University of Texas at Austin) arranged a loan of specimens of C. texana. Sten Jakobsen (Geomuseum Faxe, Faxe, Denmark) provided a cast of C.binodosa for comparison. Arden Bashfort and Laura Cotton (Natural History Museum of Denmark, Copenhagen, Denmark) granted access to their collection for comparative purposes, as did Kevin Kocot (University of Alabama) for access to the marine decapod invertebrate zoology collection and Lynn Harrell (Geological Survey of Alabama) for the fossil decapod collection. Yusuke Ando (Mizunami Fossil Museum, Japan) provided a high-resolution version of Cope etal. (2005: fig. 6) for comparison. Peter Ng (National University of Singapore) clarified ICZN rules regarding Alphacheles zeta (Rathbun, 1936) n. comb. We thank Jeff Shaw and the Nolan family for site access. We thank collectors and donors (Adam Armstrong, Gary Bielefeld, Brett Boyd, Jim Braswell, Bill Deutsch, Vic Favier via Bruce Thiel, Mark Gray, Ramsey Greene, Ron Judy, Bruce Relihan, Jason Seitz, Ikejiri Takehito, Helen Whisler) of studied specimens. This study was supported by a 2022 Paleontological Society Arthur J. Boucot Research grant to AAK. The research of MH was supported by VEGA 2/0106/23 and the Slovak Research and Development Agency under contract no. APVV-22-0523. We thank the two reviewers (Àlex Ossó and an anonymous reviewer) for their helpful comments, and Audrina Neveu for much appreciated editorial work on the page proofs. REFERENCES alCoCk a. 1896. — Materials for a carcinological fauna of India, no. 2. The Brachyura Oxystoma. Journal of the Asiatic Society of Bengal 65 (2): 134-296, pls VI-VIII. https://doi.org/10.5962/ bhl.title.16033 alCoCk a. 1900. — Material for a carcinological fauna of India. No. 6: the Brachyura Catometopa, or Grapsoidea. Journal on the Asiatic Society of Bengal 69 (2): 279-456. https://doi.org/10.5962/ bhl.title.15344 aNker a. 2010. — Ctenocheloides attenboroughi n. gen., n. sp. (Crustacea: Decapoda: Axiidea: Ctenochelidae), a new ghost shrimp with pectinate claw fingers from Madagascar. 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