David A. Waugh

NEW MIDDLE EOCENE DECAPODS (CRUSTACEA) FROM CHIAPAS, MEXICO

Abstract Decapod crustacean specimens from the middle Eocene San Juan Formation in central Chiapas represent the first record of Eocene decapods in southern México. New taxa include: Dardanus mexicanus new species (Diogenidae), Lophoranina cristaspina new species, Notopus minutus new species (Raninidae); Verrucoides stenohedra new genus and new species (Xanthidae); Stoaplax nandachare new genus and new species (Goneplacidae); and Viapinnixa alvarezi new species (Pinnotheridae). Verrucoides verrucoides new genus and new combination from the Paleocene of Greenland represents a new combination. In addition, the fauna includes Callianassa sensu lato sp., Laeviranina sp., Calappilia cf. C. hondoensis Rathbun, 1930, Eriosachila sp., and indeterminate calappid and xanthoid taxa. This assemblage bears close relationship with coeval faunas in the Tethyan region of southern Europe and southern North America and with Paleocene faunas of Greenland, strengthening the evidence for previously described patterns of dispersal within the Decapoda.

EPIBIONT PRESERVATIONAL AND OBSERVATIONAL BIAS IN FOSSIL MARINE DECAPODS

Abstract Epibionts on both living and fossil decapod crustaceans may serve as valuable proxies for paleoecological factors such as behavior and environment. Prevalence of epibionts, as observed primarily on the carapaces of fossil brachyurous decapod crustaceans, appears to be less than observed on living crabs, based upon observations in the literature, and from the study of a limited preserved biological and fossil collection. Among these factors, the three most important are that many extant epibionts do not possess skeletal structures and, therefore, are unlikely to be preserved; the epicuticle upon which epibionts attach to living brachyurans is lightly calcified and tends to be lost readily as a result of taphonomic processes; and the most common mode of preservation of fossil brachyurans is in concretions which tend to break open and leave a layer of cuticle on the counterpart, thus obscuring the potential surface of attachment of epibionts. Other factors such as the life habits of the crab, whether burrowing, burying, or remaining above the substrate; lifestyle, whether benthic or pelagic; and duration of the intermolt phase of the organism also play important roles in potential prevalence of epibionts. Careful preparation of part and counterpart remains of brachyurans as well as reference to the occurrence of epibionts in systematic studies will enhance knowledge of the host and epibiont.

Experimental Taphonomy Of Callinectes Sapidus And Cuticular Controls On Preservation

Abstract Examination of remains of Callinectes sapidus deployed in several depth and environmental settings in the Bahamas and Gulf of Mexico as part of the Shelf and Slope Experimental Taphonomy Initiative project revealed that all specimens were uniformly and strongly degraded except those in brine-seep settings. Fragmentation and loss of cuticular material at all sites was correlated to the degree of calcification within the cuticle of different skeletal elements as observed in the undeployed specimens. Claws, tips of the last anterolateral spine, and mandibles were the most durable remains. In brine-seep areas, extraordinary preservation yielded articulated skeletal elements and some soft tissue. Examination of the cuticle in control specimens with cross-polarized light and computed tomographic scanning documents the correspondence of high degrees of calcification with portions of the exoskeleton remaining after deployment.

DIFFERENTIAL CUTICLE ARCHITECTURE AND ITS PRESERVATION IN FOSSIL AND EXTANT CALLINECTES AND SCYLLA CLAWS

Abstract The microstructure of denticles in paired extant and fossil specimens of Callinectes Stimpson, 1860, and Scylla de Haan, 1833, is examined and compared to the cuticle from the remainder of the claw. Denticles of Scylla serrata and Callinectes sapidus are differentiated from the surrounding cuticle by differences in the number of pore canals, tegumental canals, density, microhardness, and phosphorous content. Differentiated denticles can be observed in fossil Scylla and Callinectes on the basis of structure and phosphorus content. Increased hardness of denticle-type cuticle functions to resist abrasion encountered during durophagy and to resist the high forces generated by the denticles as a result of their geometry. Infolds along the lateral margins of the denticles are hypothesized to allow denticles to develop beneath the old cuticle before the molt, and then to emerge and expand after the molt. Future chemical and mineralogical work involving crustaceans should take into account the presence of denticle-type cuticle and not treat the cuticle of chelae as homogeneous tissue. Because denticle-type cuticle can be recognized in the fossil record, the emergence, variation, and phylogenetic trends of this adaptation can be tested. The increased calcification of claw tips and denticles may make them even more durable than the chelae.

DECAPODA (THALASSINIDEA AND PAGUROIDEA) FROM THE EOCENE BATEQUE AND TEPETATE FORMATIONS, BAJA CALIFORNIA SUR, MÉXICO: SYSTEMATICS, CUTICLE MICROSTRUCTURE, AND PALEOECOLOGY

ABSTRACT Seven species of shrimps referable to the Thalassinoidea and four species referable to the Paguroidea have been recovered from the Eocene Bateque and Tepetate formations of Baja California Sur, México. The large number of callianassid and paguroid taxa found in these essentially equivalent, very similar formations, is unusual in the decapod fossil record. Only a few other occurrences of such large numbers of fossil paguroid and thalassinoid taxa within a single unit are known; these occurrences range in age from Eocene to Miocene. Cuticular studies indicate that callianassid chelae were bioeroded, possibly by algae. An unusual occurrence of a hash of callianassid chelae may have sequence-stratigraphic value.

Effect of calcification on cuticle density in decapods: a key to lifestyle

Abstract Measurement of density and thickness of cuticle of an array of decapod crustaceans indicates that cuticle tends to be thick and dense in benthic organisms and thinner and less dense in nektobenthic decapods. Thin section analysis of the cuticle under crossed polarized light documents a broad range of area of biomineralization. Cuticle density is strongly correlated with area of calcification. One of the nektobenthic decapods in the study exhibited no calcification of the cuticle at all, and thus exhibited the lowest density. These data support the hypothesis that density and thickness of cuticle contribute to adaptation to benthic and nektobenthic lifestyles.

Formation of Lobster-Bearing Concretions in the Late Cretaceous Bearpaw Shale, Montana, United States, in a Complex Geochemical Environment

Abstract Eleven concretions containing the nephropid lobster, Palaeonephrops browni (Whitfield, 1907), from the Upper Cretaceous (Campanian), Bearpaw Formation in northeastern Montana, were examined using visual and geochemical methods. The concretions were zoned, with an axial, phosphate-rich core also containing calcium surrounding the lobster remains and an outer, calcium-rich zone lacking phosphate. The overall composition documents these as carbonate concretions, not phosphatic concretions. Where visible, the inner zone is sheathed in a thin layer dominated by framboidal pyrite, suggesting formation by a microbial film. The different geochemical settings in the inner versus outer zones suggest reduced pH conditions during formation of the inner core and normal pH conditions resulting in formation of the outer zone. The pattern is suggestive of extremely rapid preservation of the lobster remains within a microbial sheath in which a calcium phosphate mineral, probably francolite, delicately replaced the lobster cuticle, and traces of worm (?) burrows and fecal pellets were preserved. The remainder of the concretion, the outer zone, formed under normal pH conditions and was probably induced by the chemistry of the core. Size of the concretions relative to the size of the enclosed lobsters, lack of evidence of a burrow complex in the surrounding sediment, and central positioning of the lobster remains within the concretions do not support the contention that the lobsters were entombed within a burrow.

Ontogenetic Variations in Cuticle Morphology in the Blue Crab Callinectes sapidus Rathbun, 1896

Abstract In an effort to use aspects of the cuticle as taxonomic characters in phylogenies of fossil and extant decapods, variation due to gender, growth, sample location on the carapace, and molt cycle must be understood so that taxonomically important characters can be identified. In this study, effects of sample location on the carapace and carapace size were examined. A series of male Callinectes sapidus Rathbun, 1896, specimens from 2-6 cm in length were collected on the Rhode River of the Chesapeake Bay, MD, USA. To study the effects of sample location and carapace size on parameters of the cuticle, the cuticle was examined in thin section and on the surface of the dorsal carapace. The distributional density of setal pits and nodes and node size were measured on the surface. In thin section, thickness of the cuticle and construction of the nodes and setal pits was examined. Thickness of the cuticle, node size, and setal pit density increased during growth of the crab. Node density decreased with growth. Construction of nodes and setal pits remained constant in all specimens and sample locations. Morphometric parameters of the cuticle were consistent with previously reported growth rates of the carapace in C. sapidus. Differences in the rate of change for the cuticle metrics studied occurred at carapace sizes that are attained upon reaching sexual maturity. Growth rates of cuticular features provide context for comparison with similar data in other species. In addition, the change in growth rates of these features, if recognized in fossil crab populations, may allow the determination of population age structures and size at maturity.

NEW CRETACEOUS AND EOCENE DECAPODA (ASTACIDEA, THALASSINIDEA, BRACHYURA) FROM BRITISH COLUMBIA, CANADA

Abstract A collection of Cretaceous and Eocene specimens of decapod crustaceans from southern Vancouver Island, British Columbia, Canada, has yielded the following new taxa: Cowichianassa meckerti, new genus, new species (Callianassidae); Comoxianassa haggarti, new genus, new species (Callianassidae); Preclarocarcinus parvus, new genus, new species (Homolodromiidae); and Nitotacarcinus canadensis, new species (Tumidocarcinidae). Two of the new taxa are callianassid ghost shrimp, each of which displays sexual dimorphism and is well documented from major and minor claws as well as abdomina, unusual in the fossil record and especially unusual for Cretaceous forms. Nitotacarcinus was known previously only from the Eocene of Denmark; thus, the new species extends its paleobiogeographic range dramatically. The layers in which the decapods were collected from the Paleogene Via Appia Beds were deposited in generally high-energy conditions favoring the formation of glauconite. Cuticular structures of Eucorystes platys Schweitzer and Feldmann, 2001, are described.

Decapod Crustaceans from the Maastrichtian Fox Hills Formation

Abstract Examination of all known specimens of decapod crustaceans from the Fox Hills Formation has resulted in recognition of five species and three distinctly different forms of pereiopods that cannot be assigned to a recognized taxon with certainty. Callichirus waagei n. sp. is proposed for a callianassid claw preserved within an Ophiomorpha burrow. Hoploparia sp. and Raninella oaheensis Bishop, 1978, are reported from the formation for the first time, and the cheliped of the latter species is noted, also for the first time. Latheticocarcinus shapiroi Bishop, 1988, the most common species of decapod in the formation, is re-described; the lateral flanks of this homolid crab are recognized for the first time, and the carapace is reconstructed. Necrocarcinus siouxensis Feldmann, Awotua and Welshenbaugh, 1976, is noted, but no new specimens were studied. All the decapods were preserved within concretions and all but one specimen of Hoploparia were disarticulated elements, suggesting that they may have been molted remains. Cuticle was well preserved and thin section examination of the lamellar structure of Hoploparia cuticle confirmed that, although thoroughly altered chemically, details of lamellar structure are retained.