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Crustacean Paleobiology, II

Room: Grand Ballroom South

13:30 - 15:00

Chair(s): Rod Feldmann, Carrie Schweitzer

THPM-4.1  13:30  EXCEPTIONALLY PRESERVED FOSSILS REVEAL THE ORIGINS OF CRUSTACEAN CLADES. BRIGGS DEG*, Department of Geology and Geophysics and Yale Peabody Museum of Natural History, Yale University, New Haven, CT 06520-8109, USA; SIVETER DJ, Department of Earth Sciences and Oxford University Museum of Natural History, Oxford University, Oxford OX1 3PW, UK; SIVETER DJ, School of Geography, Geology & the Environment, University of Leicester, Leicester LE1 7RH, UK; SUTTON MD, Department of Earth Sciences and Engineering, Imperial College London, London SW7 2BP, UK

The early fossil record of crustaceans is limited to sites of exceptional preservation due to the paucity of taxa with a biomineralized cuticle. Burgess Shale-type fossil deposits of Cambrian and early Ordovician age, which preserve flattened fossils primarily as carbonaceous films, continue to yield a remarkable diversity of arthropods. The great majority, however, fall low on the stem of living groups in phylogenetic analyses. Later Paleozoic fossils, preserved in three dimensions through mineralization in pyrite or calcite, postdate the initial diversification of marine arthropods and offer important insights into the earliest representatives of clades of living crustaceans. The late Ordovician Beecher's Trilobite Bed (~450 Myr BP) in upper New York State has yielded a pyritized myodocope ostracod showing brood care. Most notable, however, is the Silurian Herefordshire deposit (~430 Myr BP) in the Welsh Borderland, UK, which is a critical source of unique three-dimensional fossil arthropods, most preserving extraordinary details. Specimens from the deposit, which are reconstructed as virtual fossils based on physical-optical tomography, include a range of phyla. Among the diversity of arthropods are a marrellomorph, trilobite, pycnogonid, and horseshoe crabs, and crustaceans including several myodocopid ostracods, a pentastomid, a barnacle, a phyllocarid, and a novel form, Cascolus, which resolves as a stem-group leptostracan (Malacostraca). These early crustaceans preserve critical data on their appendages which illuminate the evolutionary history and phylogeny of the groups to which they belong. Exceptionally preserved deposits provide robust stratigraphic records that assist in calibrating the chronology of crustacean phylogeny.

THPM-4.2  14:00  THE EVOLUTION OF TRUE CRABS THROUGH TIME: INSIGHTS FROM THE TROPICAL AMERICAS. LUQUE J.*, Department of Biological Sciences, University of Alberta, Edmonton, AB T6E 2E9 Canada

A full understanding of the evolution of novel forms requires evidence of their origins. This must be inferred via study of genotypic and phenotypic variation in living forms and clues from the fossil record. However, the early evolutionary history of some morphologically diverse groups is obscure because few early-splitting branches have living descendants, molecular data are currently unavailable for many key extant species, and useful fossils are rare or incomplete. This is the case for true crabs, or Brachyura, a diverse and economically important group whose evolutionary history and phylogenetic relationships remain unresolved. Moreover, while crab fossils from higher latitudes are relatively well known, records from tropical settings are scarce and fragmentary. I present new crustacean-rich assemblages from the Mesozoic and Cenozoic of tropical America, and explore the phylogenetic relationships across the main fossil and extant Brachyura lineages in light of these new discoveries. Analyses of morphological data from fossil and extant taxa under different tree search methods support the view that podotreme brachyurans (crabs with sexual openings at the base of the legs) form a paraphyletic grade, and that some derived podotreme groups might be closer to Eubrachyura than to less inclusive podotremes. Furthermore, our findings also reveal that the evolution of shovel-like and paddle-like legs, and the loss of a typical ‘crab-like’ form, or ‘decarcinization’, have occurred independently at least five times since the Cretaceous. The versatility of the crab body form, and the interplay between development and ecological invasion, may act as drivers of morphological innovation.

THPM-4.3  14:15  A HYPERDIVERSE LATE JURASSIC SQUAT LOBSTER ASSEMBLAGE. ROBINS C.M.*, Museum of Paleontology, University of California, Berkeley, 1101 Valley Life Science Building, Berkeley, CA 94720, USA; KLOMPMAKER A.A., Department of Integrative Biology & Museum of Paleontology, University of California, Berkeley, 1005 Valley Life Sciences Building #3140, Berkeley, CA 94720, USA

Decapod crustaceans are rarely fossilized in great enough numbers for large assemblage studies. One notable exception is the Friedrich Bachmayer collection of over 7000 individual decapods from the Late Jurassic Ernstbrunn Limestone of Austria, by far the largest known Mesozoic decapod collection in the world consisting of over 80 species. The fossil galatheoid anomurans (squat lobsters) within this collection have been the subject of two taxonomic monographs in the last decade, and comprise approximately 30% of the total decapod assemblage, presenting a unique opportunity for an assemblage-level study. All identifiable carapaces, discounting external molds, were tallied, totaling 2170 specimens. Of those, 1665 were identifiable to the species-level across 53 different species, representing the richest fossil galatheoid assemblage in the world. Two species are still undescribed. Rarefaction curves for both genera and species have leveled, implying that the majority of taxa have been collected. Several diversity metrics that take into account the number of specimens per species also indicate that the assemblage is very diverse. The Shannon Index for Ernstbrunn is 2.50; for comparison, this index is only 1.12 for a mid-Cretaceous (Albian) galatheoid fauna from Koskobilo, Spain (482 individuals across 10 species). The Simpson Index (1-D) gives a value of 0.83 for Ernstbrunn and 0.58 for Koskobilo (i.e. evenness is higher for Ernstbrunn). The large assemblage also allowed for additional study of parasitic infestation prevalence, preserved as large swellings on the branchial regions of infected individuals. Infestation percentages are statistically random across species.

THPM-4.4  14:30  THYLACOCEPHALANS FROM THE CRETACEOUS LAGERSTÄTTEN OF LEBANON. CHARBONNIER S.*, Muséum national d'Histoire naturelle, UMR 7207 CR2P, CNRS-MNHN-UPMC, 8 rue Buffon, Paris

Thylacocephalans (Euarthropoda, Thylacocephala) were arthropods characterized by their “bivalved” carapace and three anterior prehensile appendages. It is still not clear how they used to live, or what their evolutionary history is. This presentation focuses on new thylacocephalans from the Late Cretaceous Konservat-Lagerstätten of Lebanon, which yielded the youngest representatives of the group. Three new genera and species are described in the Cenomanian sublithographic limestones of Hakel and Hadjoula, and two new genera and one new species are described in the Santonian chalky limestones of Sahel Alma. Among the specimens from Hakel and Hadjoula, Paradollocaris vannieri, Thylacocaris schrami and Globulacaris garassinoi are the first reports of thylacocephalans in the Cenomanian of Lebanon. Paradollocaris and Thylacocaris are assigned to Dollocarididae based upon their large optic notches limited by rostral and antero-ventral processes, their hypertrophied eyes, and their posterior notches with dorsal and ventral spines. Moreover, Thylacocaris presents a very peculiar character: an optic notch with two strong optic spines protecting the eye. Globulocaris is assigned to Protozoeidae based upon its small carapace with a distinct dorsal notch anterior to a strong postero-dorsal spine. Keelicaris deborae (Microcarididae) is also a new form in the Santonian of Lebanon. It presents a very unusual keel-shaped carapace with terraces and punctuations. The occurrence of such diverse fauna of thylacocephalans markedly increases the diversity of the group during the Late Cretaceous. The diversity and abundance of the Sahel Alma thylacocephalans pose also the problem of causes of their disappearance from the fossil record after the Santonian.

THPM-4.5  14:45  EXCEPTIONALLY PRESERVED FOSSILS OF MINUTE INFECTIVE LARVAE – 90 MILLION YEARS OLD WINDOW INTO THE EVOLUTION OF THE PARASITISM OF EPICARIDEAN ISOPODS. Schädel M.*, Department of Biology, Ludwig-Maximilians-Universität, Munich, 82152 Planegg-Martinsried, Germany ; Perrichot V., Department of Geosciences, Université de Rennes 1, 35042 Rennes, France; Haug J.T., Department of Biology, Ludwig-Maximilians-Universität, Munich, 82152 Planegg-Martinsried, Germany

Isopoda is an ingroup of Peracarida and must be considered an overall evolutionary successful group. Isopods have conquered numerous habitats from the deep sea to dry desert and exhibit various feeding strategies. In most isopods the early post-embryonic stages strongly re semble the adults. The obligate parasitic epicarideans form an exception. Their life cycle is complex and includes a host switch and extreme sexual dimorphism. This requires two highly mobile stages. One of them is the cryptoniscus larva. After detaching from its copepod larval host, it becomes plan ktic and searches for its definitive host. Within Epi caridea there are different strategies to feed on the definitive hosts right up to endoparasitism. The most specialised form is the inhabitation of the gill chamber which can be indirectly traced back to the Jurassic period, i.e. 200-142 million years ago, based on specific deformations of the hosts. Here, we present the so far oldest record of epicaridean body fossils from a rare sample of French Cretaceous amber of about 90 million years in age. This represents a rare kind of preservation where marine organisms were trapped in resin in a coastal environment. With the help of high-resolution composite fluorescence microscopy, we shed light on their highly specialised morphology that was already present in the Cretaceous and discuss implications of this find on the evolution of the synecological relationship between parasites and their hosts

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