Abstract Palaeobiological evidence of predation on ostracods derives primarily from drill‐hole traces. However, this record is limited to sparse reports and rare quantitative analyses hinder understanding of influence of predator–prey interaction in the evolution of ostracods. Moreover, predation is rarely studied in deep‐water settings. We analysed 242 drilled ostracod specimens from the relatively deep‐water strata of the Miocene Navidad Formation of Chile to assess how predation varies with size and ornamentation. Specimens of Cytherella (smooth) and Apatihowella (ornamented) and drill hole distributions were analysed using the spatial point pattern analysis of traces (SPPAT) method. Among 3425 specimens, drilling intensity was 5.38% for Cytherella and 9.78% for Apatihowella. SPPAT (of all drilling traces) revealed significant concentrations of drill holes in the dorsal–median region of Cytherella and in the ventral region of Apatihowella . Moreover, drill holes located between the valves were observed only in Apatihowella for 30% of the traces. The predators selected primarily drilling sites close the soft tissue for the smooth shelled Cytherella . In contrast, the thick dorsal shell and the strongly ornamented median regions of Apatihowella may have displaced the preferred attack site, allowing continued access to its soft tissues but toward nutritionally poorer ventral and marginal regions. Thus, ornamentation did not deter predation of the ostracod but did influence predation behaviour. Our analysis highlights the importance of ostracod shell morphology in predator–prey interactions in the ostracod fossil record in deep water settings, and calls for further research to understand the role of evolutionary escalation in ostracods.

The Late Cretaceous to Eocene alethinophidian families Palaeophiidae and Nigerophiidae comprise several taxa predominantly known from isolated vertebrae, which show adaptations for the aquatic realm. In this study, we describe seven closely associated vertebrae, which are designated as the holotype of a new snake taxon, Parapalaeophis jeffshawi gen. et sp. nov., from the Paleocene (upper Danian) Porters Creek Formation, Alabama, U.S.A. Morphologically, Parapalaeophis shows a unique combination of palaeophiid (horizontal condylar axis, anterior hypapophysis on the anterior trunk vertebrae, 'shouldered' posterior margin of the neural arch) and nigerophiid (elongate centrum, weak interzygapophyseal and subcentral ridges, lacking pterapophyses) characters, as well as the presence of posterior spurs on the prezygapophysis, which is not shared by either clade or other taxa like Tuscahomaophis. We utilized 2D landmark-based geometric morphometrics to determine the morphometric affinity of Parapalaeophis and related taxa to Palaeophiidae and Nigerophiidae. Based on the morphology and morphometrics, the new taxon is assigned to Alethinophidia incertae sedis, as assignment to either Palaeophiidae or Nigerophiidae is not justifiable. The total body length of Parapalaeophis is estimated to be 1.94 +/- 0.14 m, using a regression of vertebral lengths on body size. The vertebrae of P. jeffshawi show clear adaptations for an aquatic lifestyle. The discovery of P. jeffshawi expands the diversity and the complex morphological mosaic of Paleogene aquatic snakes, and it is among the oldest Cenozoic snakes from North America.

Abstract True crabs (Brachyura) are among the most iconic marine arthropods, representing noteworthy examples of morphological and ecological disparity. A striking feature of brachyurans are their anterior pincer-like appendages: chelipeds. These structures showcase a large diversity of morphologies that reflect ecology and overall multifunctionality. Yet, a comprehensive assessment of appendage functional morphology within phylogenetic and ecological trait contexts has never been attempted. By combining 3D geometric morphometrics, finite element analyses, multilocus molecular phylogeny, and ecological trait data for 80 crab species, including three fossil forms, we unveil a complex evolutionary history for crab chelipeds. Despite extreme shape diversity amongst chelipeds, stress distributions are very similar across taxa and hint a many-to-one pattern. High concentrations of chelipeds within constrained morphospace regions associated with peak pinch forces illustrates that brachyuran morphologies optimised for shell crushing may have arisen in the Cretaceous. Deviations from this morphospace highlight the diversification of non-shell-crushing life modes and the influence of sexual selection on appendages. Neither cheliped shape nor pinch force show phylogenetic signal. Together these results indicate that the evolution of cheliped shape is closely associated with, and inferred to have been strongly influenced by, crab ecology, biomechanical needs and sexual selection. SIGNIFICANCE STATEMENT Chelipeds, the pincer-like claws of crabs, are among the most morphologically diverse appendages within Arthropoda, yet the evolutionary forces driving this diversity remain poorly understood. By integrating 3D geometric morphometrics, biomechanical modelling, molecular phylogeny, and ecological data across 80 crab species including fossil forms, we demonstrate that cheliped morphology is driven by ecology, biomechanical demands, and sexual selection rather than phylogenetic relatedness. The multifunctionality of these structures produces strong evidence for many-to-one mapping of form to function. Morphologies optimised for durophagy appear to have originated in the Cretaceous, with subsequent diversification into manipulative and sexually selected forms from a morphologically flexible foundation. These findings demonstrate that cheliped diversity reflects a complex interplay between ecological specialisation, biomechanical optimisation, and sexual selection across Brachyura.

Crustacean cuticle in the fossil record provides insight into their preservation potential, including instances of exceptional preservation. The elemental composition of cuticular remains permit these taphonomic pathways to be explored. This study uses energy dispersive X-ray spectroscopy to examine the exoskeletal elemental composition of five crustacean taxa-Bombur complicatus, Caryocaris curvilata, Mecochirus sp., Sculda syriaca, and Tealliocaris woodwardi-ranging from the Ordovician to the Cretaceous. We also compare the composition of these fossil forms to modern species to explore changes within the group. We document calcium and phosphorus as dominant elements across most fossil specimens. As modern crustaceans use calcium carbonate extensively, this result suggests one of two explanations: either the original exoskeleton of these extinct crustaceans was composed of both calcium carbonate and phosphate or its fossil composition was the result of diagenetic phosphatization in anoxic environments. The higher levels of phosphorus in fossil taxa compared with modern taxa highlights the current lack of easy criteria to determine whether the mineralogical component of a fossil exoskeleton has been diagenetically altered. To this end, we present future directions for addressing this complication. Furthermore, Mecochirus sp. cuticle is predominantly composed of carbon, demonstrating an alternate preservational pathway that cannot be distinguished from the other examples based on a visual examination under visible light alone. Its preservation is likely linked to modification of organic compounds. Our findings and discussions underscore a complex interplay of environmental and geochemical factors in crustacean fossilization, uncover novel examples of preservational routes, and illustrate how energy dispersive X-ray spectroscopy (EDS) elucidates exoskeletal preservation.

Paleontology provides insights into the history of the planet, from the origins of life billions of years ago to the biotic changes of the Recent. The scope of paleontological research is as vast as it is varied, and the field is constantly evolving. In an effort to identify “Big Questions” in paleontology, experts from around the world came together to build a list of priority questions the field can address in the years ahead. The 89 questions presented herein (grouped within 11 themes) represent contributions from nearly 200 international scientists. These questions touch on common themes including biodiversity drivers and patterns, integrating data types across spatiotemporal scales, applying paleontological data to contemporary biodiversity and climate issues, and effectively utilizing innovative methods and technology for new paleontological insights. In addition to these theoretical questions, discussions touch upon structural concerns within the field, advocating for an increased valuation of specimen-based research, protection of natural heritage sites, and the importance of collections infrastructure, along with a stronger emphasis on human diversity, equity, and inclusion. These questions offer a starting point—an initial nucleus of consensus that paleontologists can expand on—for engaging in discussions, securing funding, advocating for museums, and fostering continued growth in shared research directions.

The fossil record is an outstanding data source for understanding predator-prey interactions. Although drill holes are relatively well studied in calcareous metazoans, their record in ostracods is sparse compared to other taxa (e. g., gastropods and bivalves). Based on an extensive literature review, we have compiled the Phanerozoic record of drill holes in Ostracoda to identify patterns in predator-prey interactions in these crustaceans. Our results show that most research has is on Cenozoic material and is concentrated in Europe, especially in Spain and Italy. Although drilling predation on ostracods is presentd since the Silurian, drilling intensity appears quantifiable and more common from the Cretaceous onwards. Drill holes are predominant in the central region of carapaces in the Cenozoic and are identified as the ichnospecies Oichnus paraboloides and Oichnus simplex. Compared to Mesozoic and Paleozoic records, the predator-prey size ratio increased dramatically after the K-Pg boundary. Null model analysis suggests that some ostracod genera were preferentially preyed on, unrelated to their relative abundance. Our data demonstrate that the drilling intensity was lower in the Mesozoic than the Cenozoic, a pattern observed for the first time in Ostracoda. Finally, our paper also identifies various knowledge gaps and opportunities to further study predation in ostracods.

Among various drill holes located in ancient shells, the ichnospecies Oichnus ovalis is particularly important for understanding the presence and behaviour of cephalopods. In modern seas, incirrate octopuses of the superfamily Octopodoidea produce small, oval drill holes ascribed to O. ovalis in the shells of various molluscs and crustaceans. Until now, fossil O. ovalis has been primarily known mostly from the Pliocene and Pleistocene, whereas the oldest examples have been reported from the Late Cretaceous (Campanian). Here, we describe the first Jurassic record of O. ovalis, found in the ammonite Quenstedtoceras lamberti from the Middle Jurassic (latest Callovian) of Russia. The oval drill hole measuring 1.0 to 0.5 mm is located on the ammonite body chamber in the area of attachment of retractor muscles, which suggests this hole most likely was made by a predator that attacked a living ammonite in the water column. If this drill hole had been found in the Late Cretaceous or Cenozoic, it would have been attributed to an octopodoid predator. However, body fossils of octopodoids are still unknown from the Jurassic. Nevertheless, judging by some molecular clock data, incirrate octopuses might have already existed in the Late Jurassic and probably even earlier. Therefore, the Jurassic O. ovalis may have been drilled by one of the oldest octopodoids, their ancestors, or an unknown predator. Regardless of the identity of the predator, this finding expands our knowledge on the Middle Jurassic predators of ammonoids and suggests drilling on active pelagic prey arose during the Jurassic phase of the Mesozoic Marine Revolution. Oichnus, Oichnus ovalis, square Jurassic, Callovian, ammonites, ichnotaxa

AbstractPredator–prey relationships are considered a major driver for the evolution of organisms, and thus contributed to shaping morphology, ecology, and diversity. During the Late Cretaceous of North America, ammonoid cephalopods were one of the most abundant and diverse marine invertebrates. Despite frequent reports of shell breakage in ammonoids, little is known pertaining to the frequency, position, and size of the shell break through a stratigraphic succession. In this study, we analyze an extensive collection of the scaphitid ammonoid Hoploscaphites nicolletii, which exhibits shell breakage, from the Upper Cretaceous (Maastrichtian) Fox Hills Formation in South Dakota, USA. We focus on four upper Maastrichtian assemblage zones listed stratigraphically from bottom to top—the lower nicolletii Assemblage Zone (LNAZ), the Limopsis-Gervillia Assemblage Zone (LGAZ), the upper nicolletii Assemblage Zone (UNAZ), and the Protocardia-Oxytoma Assemblage Zone (POAZ). Within the collection, we observed two primary types of breakage: ventral and lateral, each displaying a relatively consistent geometry. Lateral breaks, measuring a few centimeters, represent about 20–40% of the maximum conch diameter. Ventral breaks are slightly larger, representing 30–70% of the diameter. Both breakage types occur in the body chamber at approximately 90° from the aperture extending to near the last septum. We find that the incidence of injury increased from 6.6 to 13.7% with some fluctuation across the zones. The breakage size relative to body size does not exhibit a clear change across the assemblage zones. Additionally, no significant difference is apparent in the body size between injured and uninjured specimens within each zone. A weak positive correlation between the size of lateral breaks and maximum conch diameter in LNAZ suggests a tendency for larger predators to target larger individuals. Given the consistency of geometry and size, we presume that these breaks represent lethal injuries from durophagous predators. We propose coleoid cephalopods as the likely culprits for ventral injuries, although fish and crustaceans are plausible alternatives. Concerning lateral injuries, decapod crustaceans appear to be the most probable durophagous predators.

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 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.

Malacostracan crustaceans are very diverse today, but their evolutionary history and biodiversity during the Paleozoic remain understudied. One clade within Malacostraca is Belotelsonidea, crustaceans with a shrimp-like body plan only known from the Carboniferous. We describe the fourth species of this group, Lobetelson feldmanni n. sp., from the Pennsylvanian (Kasimovian) of the Kinney Brick Quarry, New Mexico, USA. The holotype is a flattened, relatively complete specimen with an eye preserved. A second, less well-preserved specimen from the same locality might be referable to the new species. This record represents the youngest record of Belotelsonidea, now ranging from the upper Tournaisian to the Kasimovian, equivalent to ca. 40 Myr. Paleobiogeographically, belotelsonids are only known from Scotland and various parts of the USA thus far, located near the equator to ~20° south during the Carboniferous. Whereas most belotelsonids are thought to have lived in a marine environment, some of the oldest specimens from Scotland are interpreted to have inhabited areas with limited to no marine influence. UUID: https://zoobank.org/6c52b87d-9259-4b19-85c7-71b425bb6187

The brachyurans Tehuacana tehuacana Stenzel, 1944 and Dromilites americana Rathbun, 1935 have historically been difficult to place in families. A reevaluation of type and referred material from several institutions suggests that the two species are referrable to separate genera in Palaeoxanthopsidae. Hyphalocarcinus new genus is erected to accommodate H. americanus new combination, and Tehuacana remains a distinct genus. Palaeoxanthopsidae evolved and radiated in the Atlantic Ocean, ranging from Late Cretaceous (Maastrichtian) to early Eocene (Ypresian) in age. This work adds to the known diversity of Palaeoxanthopsidae and demonstrates that the family survived and thrived in the Atlantic Ocean in the wake of the end-Cretaceous extinction. Differential preservation of specimens must be evaluated carefully when placing superficially similar taxa at the family, genus, and species level. UUID: http://zoobank.org/73da26c7-aff7-4abe-8aa5-768944bbf6ee

Marine isopod fossils represent a small component of the crustacean fossil record, contrasting the exceptional modern diversity of marine representatives of Isopoda. Examination of previously documented isopod species therefore presents an opportunity to derive additional paleobiological and taphonomic insight of these rare fossils. Here we consider two clusters of Archaeoniscus brodiei from the Lower Cretaceous (middle to upper Berriasian) Intermarine Member of the Durlston Formation, England. The individuals within the clusters are mostly complete, of similar size ranges, and are preserved on two different bedding planes. After examining these individuals, we illustrate, for the first time, appendages and eyes of A. brodiei. The appendage morphology supports the interpretation of A. brodiei as an isopod adapted to a benthic lifestyle. We propose that isopods from the Durlston Formation follow similar taphonomic pathways to arthropods preserved within plattenkalk-like deposits, resulting in enrichment in calcium carbonate and phosphate. Finally, the clusters reflect gregarious activities that were preserved during hypoxic events brought on by concurrent decay of algal blooms.

Gregarious behaviours in modern and fossil arthropods are commonly associated with defensive strategies, mass moulting and synchronous reproduction. Such behaviour is scarcely documented in the crustacean fossil record. Identifying clusters in extinct Pancrustacea is, therefore, important for understanding the evolutionary history and origin of crustacean gregariousness. Cyclida, an order of extinct, enigmatic pancrustaceans that have been subject to limited palaeoecological examination, represents an ideal group for testing the presence of gregarious behaviour. Here, we report a cluster of 50 Schramine montanaensis individuals from the Serpukhovian-aged Bear Gulch Limestone of Montana, USA, expanding the exceptionally rare record of cyclidan aggregations. The presence of articulated specimens with appendages and possible gill preservation supports the interpretation of carcasses that were preserved during a rapid burial event. We propose that this cluster records either a mass moulting event or clustering for shelter, representing one of the oldest records of crustacean gregariousness. These findings provide important insights into cyclidan life modes and ecological interactions in Carboniferous marine environments.

This article focuses on Jurassic and Cretaceous crinoids found in the central part of the southern Tethys shelf. The specimens presented herein come from African and Asian countries (from west to east: Morocco, Algeria, Egypt, Ethiopia, Kenya, Lebanon, Jordan, Madagascar, and India). These records are based on the study of over 30,000 crinoid remains, including cups, thecae, centrodorsals, radials, basals, brachials, columnals, pluricolumnals, cirri, and cirrals. Among the stalked crinoids, 36 isocrinid, 7 cyrtocrinid, 8 comatulid, 1 incertae sedis , and several millericrinid taxa were recorded from northern and eastern Africa, the Middle East, and India. The free-swimming roveacrinids are represented by 39 taxa. We note that the number of millericrinid taxa has been overestimated and, hence, this group requires a thorough reevaluation. All crinoids were classified as stalked isocrinids, Isocrinida (Seirocrinus subangularis, Balanocrinus subteres, B. pentagonalis, B. gillieroni, B. cf. ticinensis, Percevalicrinus sp., P. aldingeri, Isocrininae indet., Isocrinus legeri, I. nicoleti, I. dumortieri, I.? lissajouxi, I.? granosus, Chariocrinus andreae, C. basaltiformis, Pentacrinites sp.), cyrtocrinids, Cyrtocrinida (Cyrtocrinina indet., Eugeniacrinites sp., Apsidocrinus sp., Phyllocrinus belbekensis, Ticinocrinus moroccoensis, Hemibrachiocrinus sp.), comatulids, Comatulida (Bourgueticrinus sp., Ausichicrinites zelenskyyi, Semiometra algeriana n. sp., Comatulina infracretaceus, Copernicrinus zamorae, Comaturella pinnulata), and millericrinids, Millericrinida (Millericrinida fam. et gen. indet, Millericrinus annulatus, M. charpyi, M. horridus, and M. munsterianus). The remains of free-swimming roveacrinids (Roveacrinida) are also documented and represented by isolated thecae, radials, basals, spines, and brachials. Numerous remains of roveacrinids are visible in thin sections; these will be published elsewhere. Additionally, a critical systematic review of the crinoids mentioned and illustrated in the literature is also provided. The millericrinid remains from the Campanian of Alabama, southeastern USA, were used for comparative purposes and represent the youngest occurrence of the order Millericrinida in the world thus far. The abundance of crinoid genera between the northern and southern Tethys parts is shown to be significant. However, the number of crinoids in Africa, the Middle East, and India remains underestimated. Possible reasons for this underestimation are provided.

Mantis shrimp (Stomatopoda) are extant, marine, predatory arthropods, but these malacostracan pancrustaceans are also occasionally preserved in fossil assemblages, particularly in Carboniferous and Cretaceous deposits. Carboniferous species fall into two suborders-Palaeostomatopodea and Archaeostomatopodea-and represent the ancestral forms that gave rise to modern lineages. Herein, we describe hitherto unknown specimens belonging to the archaeostomatopod genus Tyrannophontes from the Pennsylvanian-aged Wea Shale Member, eastern Nebraska. We explore the preservation of these fossils using scanning electron microscopy and energy dispersive X-ray spectroscopy. These approaches reveal additional morphological characteristics, including unique appendicular data, such as the earliest occurrence of biramous gilled appendages in Stomatopoda. We suggest that further examination of black shales will likely uncover novel records of these rare pancrustaceans.

Predation is a behavior that is commonly unsuccessful, but the cause of failure is often difficult to determine in the fossil record. Here, we report on gastropod drill holes in two Plio- and Miocene bivalve specimens from the Netherlands created from the inner side of the bivalve prey's shell, which we call reverse drill holes. These holes are unequivocally caused by failure of the gastropod drilling predators to make effective use of their chemoreception and mechanoreception sensory adaptations. We hypothesize that the diffuse nature of chemical cues emanating from dense aggregations of living prey could have confused foraging predators and stimulated them to initiate the drilling process on empty valves. Poor decision making due to hunger is an alternative hypothesis. These traces represent the fi rst reported examples of reverse gastropod drill holes from the fossil record, and the fi rst attributed to Naticidae. Compared to other types of failed predation (incomplete drill holes and drill holes in multiply-drilled specimens) in the two assemblages studied, reverse drill holes are rare (< 1% of drill holes). This result implies that the driller's sensory and decision-making processes were generally reliable at distinguishing dead from live prey.

The fossil record of parasitism is poorly understood, due largely to the scarcity of strong fossil evidence of parasites. Understanding the preservation potential for fossil parasitic evidence is critical to contextualizing the fossil record of parasitism. Here, we present the first use of X-ray computed tomography (CT) scanning and finite elements analysis (FEA) to analyze the impact of a parasite-induced fossil trace on host preservation. Four fossil and three modern decapod crustacean specimens with branchial swellings attributed to an epicaridean isopod parasite were CT scanned and examined with FEA to assess differences in the magnitude and distribution of stress between normal and swollen branchial chambers. The results of the FEA show highly localized stress peaks in reaction to point forces, with higher peak stress on the swollen branchial chamber for nearly all specimens and different forces applied, suggesting a possible shape-related decrease in the preservation potential of these parasitic swellings. Broader application of these methods as well as advances in the application of 3D data analysis in paleontology are critical to understanding the fossil record of parasitism and other poorly represented fossil groups.

The south-central margin of the Jaca Basin (South-central Pyrenees, Spain) offers well-exposed outcrops ideal for studying the distribution of decapod crustaceans across a mixed carbonate-siliciclastic depositional system during the middle-late Eocene (Bartonian-Priabonian). This study encompasses an area of 1000 km2, featuring environments from siliciclastic coastal plains and deltaic complexes to shallow carbonate and mixed platforms, including coral reefs, extending to prodelta/outer platform deeper conditions. Detailed sampling in four depositional sequences yielded 372 fossil decapod specimens from various lithofacies across 20 localities. Our analysis identifies 39 decapod species within 22 families and demonstrates ecological zonation of decapods in shallow to relatively deep environments. Diversity peaks in siliciclastic shallow proximal prodelta areas and carbonate bryozoan meadows. Species distribution between carbonate and siliciclastic facies is similar, though taxonomically distinct. Articulated specimens predominantly occur in shallow proximal and relatively deep distal siliciclastic areas, linked to sudden sediment input and high sedimentation rates. These findings elucidate the spatial and temporal distribution factors of decapod crustaceans during the middle-late Eocene, contributing to the broader understanding of palaeoecological patterns in mixed depositional systems.