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JVP 26(3) September 2006—ABSTRACTS 35A JOURNAL of VERTEBRATE PALEONTOLOGY

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JVP 26(3) September 2006—ABSTRACTS 35A JOURNAL of VERTEBRATE PALEONTOLOGY Neoceti Symposium, Saturday 8:45 acid-prepared osteolepiforms Medoevia and Gogonasus has offered strong support for BODY SIZE AND CRYPTIC TROPHIC SEPARATION OF GENERALIZED Jarvik’s interpretation, but Eusthenopteron itself has not been reexamined in detail. PIERCE-FEEDING CETACEANS: THE ROLE OF FEEDING DIVERSITY DUR- Uncertainty has persisted about the relationship between the large endoskeletal “fenestra ING THE RISE OF THE NEOCETI endochoanalis” and the apparently much smaller choana, and about the occlusion of upper ADAM, Peter, Univ. of California, Los Angeles, Los Angeles, CA; JETT, Kristin, Univ. of and lower jaw fangs relative to the choana. California, Davis, Davis, CA; OLSON, Joshua, Univ. of California, Los Angeles, Los A CT scan investigation of a large skull of Eusthenopteron, carried out in collaboration Angeles, CA with University of Texas and Parc de Miguasha, offers an opportunity to image and digital- Marine mammals with homodont dentition and relatively little specialization of the feeding ly “dissect” a complete three-dimensional snout region. We find that a choana is indeed apparatus are often categorized as generalist eaters of squid and fish. However, analyses of present, somewhat narrower but otherwise similar to that described by Jarvik. It does not many modern ecosystems reveal the importance of body size in determining trophic parti- receive the anterior coronoid fang, which bites mesial to the edge of the dermopalatine and tioning and diversity among predators. We established relationships between body sizes of is received by a pit in that bone. The fenestra endochoanalis is partly floored by the vomer extant cetaceans and their prey in order to infer prey size and potential trophic separation of and the dermopalatine, restricting the choana to the lateral part of the fenestra. The nasal generalized fossil cetaceans. Methods for predicting body size of fossil taxa from three cavity is proportionately much shorter than in Jarvik’s reconstruction, possibly because the occipital measures (bicondylar breadth; foramen magnum and occipital condyle areas) were latter was based on two specimens that were incorrectly aligned. also developed using allometric models determined from measurements made on >2500 skulls representing all extant species. Models for body size prediction were confirmed for Poster Session III numerous fossil taxa with well-preserved axial postcrania. Enhanced by inclusion of addi- THE DICROSTONYX PARADOX, NEW EVIDENCE FROM A 40,000 YBP MICRO- tional parameters describing the feeding apparatus (tooth density; tooth row length and FAUNA, JAGUAR CAVE EASTERN IDAHO position; rostrum length/breadth; tooth cross-sectional area and eccentricity as measured at AKERSTEN, William, Idaho State Univ., Pocatello, ID the enamel-dentine juncture), body size was found to be a useful predictor of prey size in All modern Dicrostonyx are well adapted to arctic tundra conditions; consequently, generalized cetaceans. We used body size and these other parameters to infer trophic roles Pleistocene occurrences have been viewed as definitive evidence of past tundra conditions for a large number of Oligocene and Miocene cetaceans with unspecialized feeding anato- and disharmonious associations. A few have suggested that the evidence is more compat- my. Overall, trophic diversity of generalized cetaceans was low in the Oligocene, but ible with a change in the ecological requirements of Dicrostonyx. A very fossiliferous 160 increased dramatically in the Middle-Late Miocene and later. This transition marks the cm section recently excavated in 20 cm increments from Jaguar Cave at the base of the extinction of squalodontids and other pre-neocete lineages and rise and diversification of Beaverhead Mountains dates from 39,120 BP to >48,400 BP. The matrix is comprised of the Neoceti, and superficially suggests that the Neoceti competitively displaced its ances- small, interlocking siliceous limestone fragments weakly cemented by loess, very difficult tors. However, major changes in oceanographic conditions (including latitudinal stratifica- to excavate, which would have all but eliminated mixing of levels. Small numbers of tion of oceans and increased coastal upwelling) and changes in the prey base utilized by Dicrostonyx groenlandicus occur through most or all of the section (not all levels have yet cetaceans were also occurring during this time, rendering simple competitive scenarios for been completely processed and studied) in disharmonious association with Lemmiscus, this transition untenable. We suggest that numerous factors played a role in the rise and other small mammals, and as yet unidentified snakes and lizards. While the mammal asso- diversification of the Neoceti, but their adaptability to changing environmental conditions ciation can readily be explained an example of a disharmonious association, the association was a major factor accounting for their success. of snakes and lizards with a supposed tundra form is extremely difficult to explain. The key taxon appears to be Dicrostonyx; its adaptations may be more related to deep snow, not Poster Session III necessarily to tundra conditions. I suggest that its present distribution, allopatric (except DYNAMICS OF ENVIRONMENTAL CHANGES DURING THE LATE PLEIS- for a modest overlap) with the widespread and very adaptable Microtus pennsylvanicus, has TOCENE IN THE ALTAI MOUNTAINS (RUSSIA, WESTERN SIBERIA) BASED resulted from its having been gradually outcompeted by the latter over much of its original ON MAMMAL AND MOLLUSK DATA FROM PALEOLITHIC ARCHEOLOGI- range, remaining only in its present tundra refugia. One explanation for the co-occurrence CAL SITES of Dicrostonyx and small reptiles at Jaguar Cave 40,000 years ago is that the winters had AGADJANIAN, Alexandre, Paleontological Institute RAS, Moscow, Russia; KON- fairly deep snows which favored the adaptations of Dicrostonyx, but the summers were rel- DRASHOV, Peter, Northwest Missouri State Univ., Maryville, MO atively warm and long enough for small reptiles to reproduce and obtain adequate food for Faunal studies aimed for the reconstruction of the paleoenviroment of the late Pleistocene winter hibernation. My interpretation is that North American Dicrostonyx is an indicator and its dynamics during the time of prehistoric man were conducted through the analysis of of substantial snow depth but may or may not be an indicator for tundra conditions. extant biota and through the study of the fossil biota including mollusks, birds, and mam- mals from the deposits of the Paleolithic archeological sites. Nine major extant plant asso- Marine Reptiles Symposium, Wednesday 2:00 ciations, each with its specific mammal and mollusk fauna, were identified. The most typi- AN UPDATE ON NEW MARINE REPTILES FROM THE TROPIC SHALE OF cal existing association in the northwestern Altai Mountains is the taiga with scattered SOUTHERN UTAH alpine and steppe elements. Extinct communities of mammals, birds and mollusks in the ALBRIGHT, L., Univ. of North Florida, Jacksonville, FL; GILLETTE, David, Museum of Altai Mountains went through significant faunal changes during the late Pleistocene- Northern Arizona, Flagstaff, AZ; TITUS, Alan, Grand Staircase-Escalante National Holocene. Most of the biotic changes were caused by climate, but some could have result- Monument, Kanab, UT ed from the influence of prehistoric man. Climatic changes caused abrupt decrease of the Fieldwork conducted in the Tropic Shale of southern Utah, ongoing since 2000, has result- nival and steppe elements in the biota and increase in the number of taiga species. Despite ed in the recovery of several specimens of short-necked plesiosaurs representing both the these changes many species survived the Pleistocene/Holocene transition. Presence of Polycotylidae and the Pliosauridae. Although these specimens have been reported in pre- Siberian species in both extinct and extant Altai faunas indicates that changes in the ecolog- vious abstracts, completion of our studies has resulted in revised conclusions. Of three dif- ical composition of the paleocommunities occurred in otherwise zoogeographically stable ferent polycotylids recovered, it has been determined that two represent new taxa. In addi- environment. Changes in the composition of the biota of the studied region occurred tion to the known Trinacromerum bentonianum, one of the new taxa appears to share a sis- through the “recruitment” of taxa from other regions of Altai Mountains and adjacent terri- ter taxon relationship with the late Santonian/early Campanian Polycotylus latipinnus. The tories. Using a combined approach and including such groups as mollusks in the analysis second new taxon, together with new unnamed taxa from the late Cenomanian of South allowed us to confirm and more precisely describe the dynamics of the paleoenvironmental Dakota and Japan, represents a new clade of polycotylids based primarily on the distinctive changes in the late Pleistocene and Holocene. Number of bones of small and large mam- morphology of certain paddle elements. Representing the Pliosauridae are two new speci- mals as well as the number of Paleolithic artifacts showed that prehistoric man had an mens of Brachauchenius lucasi, both of which include skull material and one of which important influence on the paleoenviroment of the ecosystems of the Altai Mountains. includes pectoral and pelvic elements previously unknown for this taxon. Although the Previously conducted studies show that prehistoric man occupied
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