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Wednesday Morning, November 3, 2004 WEDNESDAY MORNING, NOVEMBER 3, 2004 ROMER PRIZE SESSION PLAZA BALLROOM A/B MODERATORS: RYOSUKE MOTANI AND RAYMOND ROGERS 8:00 Welcome 8:15 Beck, A.: THE ORIGINS OF MAMMALIAN LOCOMOTION: NEW METHODS FOR RECONSTRUCTING POSURE IN EXTINCT NON-MAMMALIAN SYNAPSIDS BECK, Allison, Univ. of Chicago, Chicago, IL The Synapsida, composed of living mammals and their extinct ancestors, are colloquially known as the ‘mammal-like reptiles.’ The extensive fossil record captures numerous transitional forms recording the transition from Permian, reptile-like pelycosaurs to primitive therians of the Triassic. A major part of this transition involved a change from a sprawling posture to one similar to the crouched posture of living small mammals such as the opossum. Despite our understanding of the postural endpoints, the question remains: What was the locomotory posture of taxa that are phylogenetically intermediate between pelycosaurs and modern mammals? Two major notions of postural change have been proposed, both supported by functional morphologic analyses and comparison to living mammals and reptiles. One suggests that intermediate taxa were capable of a dual-gait, much like modern crocodilians. The other outlines a series of increasingly upright intermediates. Neither hypothesis has been quantitatively evaluated. Here I set up a framework for interpreting function in extinct vertebrates, and apply it to reconstructing posture in extinct non-mammalian synapsids. Linear and angular measurements were taken on the limb and girdle bones of extant iguanian and varanid lizards, crocodilians, therian mammals and monotremes, and again on fossil synapsids. Multivariate and bivariate analyses were used to correlate suites of morphologic features with posture in the living forms. The data for fossil taxa were then filtered through these morphological correlates and examined for patterns. Fossil taxa that are morphologically similar to modern taxa can be inferred to have similar locomotory posture, and reconstructions can be constrained beyond previous concepts. The quantitative results demonstrate that intermediate synapsids followed the latter pattern, evolving through a series of increasingly upright forms. These results show, however, that both the forelimb and hindlimb became more upright earlier in synapsid evolution than previously thought. Future work will incorporate quantitative analyses of qualitative data to more fully understand synapsid postural evolution. 8:30 Burris, J.: MORPHOLOGY AND PHYLOGENETIC IMPLICATIONS OF RECENT AND FOSSIL CARCHARHINIFORM SHARK VERTEBRAL CENTRA BURRIS, John, Michigan State Univ., East Lansing, MI The cross-sectional anatomy of secondary calcifications of shark vertebral centra has featured in phylogenetic hypotheses, although never in a rigorous cladistic framework. In this study, the internal calcification patterns, along with the external morphology, of fossil and Recent shark centra of the Order Carcharhiniformes have been coded and subjected to a cladistic analysis to address the utility of centrum features for revealing relationships. Carcharhiniform sharks were selected as a study group because they are a monophyletic clade with reasonably well understood intraordinal relationships, a rich fossil record, and readily available Recent comparative skeletal material. External characters include centrum proportions, the presence and distribution of cartilage canals, and the size, shape, and spacing of the foramina for the basidorsal and basiventral arch components. The internal calcification features evaluated include the morphology and spacing of the four intermedialia, the four noncalcified areas, and the four diagonal calcifications. Centrum characters were analyzed both separately and combined with other morphological characters from previous analyses. Results of the cladistic analysis show that shark centrum characters are useful for elucidating phylogeny. Tree topology was very similar for both analyses, and similar to recent molecular databased phylogenies. The addition of centrum data to shark phylogenetic analyses will allow for a more objective means of determining the interrelationships of fossil and extant carcharhiniform sharks than studies based on teeth alone, with their well-documented difficulties. The data gathered will also be important for future studies to interpret the relationship between centrum morphology and swimming characteristics in extant and, ultimately, extinct taxa. 8:45 Ehret, D.: SKELETOCHRONOLOGY AS A METHOD OF AGING OLIGOCENE GOPHERUS LATICUNEUS AND STYLEMYS NEBRASCENSIS, USING GOPHERUS POLYPHEMUS AS A MODERN ANALOG EHRET, Dana, Univ. of Florida Dept of Geological Sciences, Gainesville, FL The use of skeletochronology in many reptile groups has become a commonplace method of incremental growth analysis over the last twenty years. This method has been largely overlooked as a feasible alternative to scute annuli counts or carapace length measurements in tortoises. Incremental growth layers in other reptiles and amphibians have been correlated to annual growth cycles. In bone thin sections, a light, wide band represents a season of rapid growth, and a thin, dark band represents a season of slow growth or stasis, making up a single year’s growth. Growth layers are analyzed by taking determined-thickness thin-sections from humeral shafts of specimens. Information gathered from Gopherus polyphemus specimens, from north central Florida, provides the groundwork for the use of skeletochronology in the fossil tortoise species Gopherus laticuneus and Stylemys nebrascensis, from the Nebraska badlands. Information derived from incremental growth assessment includes approximate age of the individual. In turn, this data can be used as a starting point to determine the population dynamics of a group of individuals. Other aging techniques (i.e., scute annuli counts and shell dimensions) can be misleading, and are highly population specific. Skeletochronology is an accurate method of aging that can be applied to both fossil and modern tortoise populations. 9:00 Fox-Dobbs, K.: SURVIVING THE LATE PLEISTOCENE EXTINCTION: WERE MARINE RESOURCES A DIETARY BUFFER WITHIN THE VULTURE GUILD? FOX-DOBBS, Kena, Univ. of California Santa Cruz, Santa Cruz, CA The late Pleistocene extinction decimated terrestrial megafaunal communities in North America, but did not affect marine mammal populations. In coastal ecosystems the carnivore and scavenger species that fed on marine megafauna may have been buffered from the extinction and survived into the Holocene. Here, I use stable isotope data to test this hypothesis by characterizing the feeding preferences of the largest members of the Pleistocene vulture guild. I analyze two regionally extinct species (Teratornis merriami - teratorn; Coragyps occidentalis - western black vulture) and one extant species (Gymnogyps californianus - California condor) from southern California. All three species were abundant in this area until the Pleistocene-Holocene boundary, after which the teratorn and western black vulture disappeared along with the megafauna. Modern condors have been observed scavenging both marine and terrestrial resources, and this dietary flexibility may have been the key to their survival. Carbon and nitrogen ratios are much higher in marine than in terrestrial ecosystems, and as such provide a clear marker of the relative contributions of these resources to animal diets. To track the influence of marine resources in the ancient vulture guild I analyzed the isotopic ratios of collagen from bones collected from several late Pleistocene sites. I used isotope data from multiple abundant herbivore and carnivore megafaunal species to characterize terrestrial resources. Carbon and nitrogen isotope values for all teratorn and western black vulture individuals are within the terrestrial range of values, and therefore do not imply any significant marine resource utilization. The condors are split into two groups of individuals; those with lower isotope values indicating a terrestrial-based diet, and those with higher values indicating a strong marine influence. Unlike the teratorn and western black vulture, Pleistocene condors were able to feed across the terrestrial-marine interface. These findings suggest that the survival of vulture species into the Holocene was more strongly correlated to a marine versus terrestrial diet. 9:15 Hall, M.: A NEW APPROACH FOR INFERRING ACTIVITY PATTERN IN AVIANS USING THE ORBIT AND SCLEROTIC RING HALL, Margaret, SUNY, Stony Brook School of Medicine, Stony Brook, NY Activity pattern (e.g., nocturnal, diurnal, and arrhythmic) is a significant component of an animal’s ecology, but the evolution of activity patterns among terrestrial vertebrates is poorly studied. Data on the activity patterns of fossil vertebrate taxa are required to reconstruct the basal character states of vertebrate groups. In addition, these data are significant for reconstructing the paleobiology of individual fossil taxa. In order to determine to what extent activity pattern can be reconstructed in fossil taxa, anatomical correlates of activity pattern in extant taxa must be identified. Avians are useful for this reason because activity pattern and gross eye shape are strongly correlated. For example, photopic- adapted eyes have larger axial lengths relative to their corneal diameters, an adaptation for increasing focal length, which enlarges the image and heightens visual acuity. In addition, scotopic-adapted eyes exhibit enlarged corneal diameters relative
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