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Session Schedule & Abstracts

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Saturday 2nd July, 2016

Symposium: New insights into the functional relationship between anatomy and physiology of extinct and extant vertebrates 1

Room: Salon F   2:30 pm–4:00 pm

Moderator(s): W. R. Porter & G. Tattersall
PHY1-1  2:30 pm  Vascular anatomy and thermophysiological strategies in the heads of extinct and extant dinosaurs. Porter WR*, Ohio University Heritage College of Osteopathic Medicine; Witmer LM, Ohio University Heritage College of Osteopathic Medicine
Abstract: Diapsids emphasize different sites of thermal exchange (oral, nasal, and orbital regions), yet share conserved vascular patterns known to facilitate thermoregulation. Given the impact of surface-to-volume ratio on heat balance, we hypothesized that the higher heat loads of large-bodied dinosaurs would require enhanced sites of cephalic thermal exchange, potentially promoting selective brain cooling (SBC), in comparison with smaller-bodied members of the same clade. Evidence for vascular anatomy was collected from dinosaur fossils and their extant relatives using CT scans, vascular injection, and/or gross dissection. Cross-sectional areas of bony vascular canals were measured and analyzed using principal components and partial least squares analyses to test hypotheses of thermally-relevant vascular networks in small- and large-bodied dinosaurs of the same clade. Generalized vascular patterns and equivalent vascular canal sizes were found in smaller-bodied dinosaurs with modest-sized oral and nasal regions. Large-bodied dinosaurs likely experienced selective pressures to emphasize regions of physiological heat-exchange, and indeed the blood vessels in these emphasized sites were found to have different sizes and combinations of blood vessels. Sauropods had a large subnarial foramen indicating a rich blood supply to the nasal and oral regions. Ankylosaurs had evidence of an enhanced blood supply to the nasal region, but not to the oral region. Theropods had modest supply to nasal and oral regions but an enhanced blood supply to the paranasal sinuses, indicating a novel physiological role for these sinuses. This evidence supports the hypothesis that larger-bodied dinosaurs evolved anatomically expanded and richly vascularized sites of thermal exchange to support the SBC necessary to buffer neurosensory tissues from extreme body temperatures. Moreover, different clades evolved different vascular strategies, reflecting convergent evolution of large size and different evolutionary paths to SBC.

PHY1-2  2:45 pm  Avian bills as thermoregulatory structures. Tattersall GJ*, Brock University
Abstract: Avian bills rest at the cross-roads between form and function. Known for their diversity of forms as adaptive feeding structures, bills are also mechanosensory, chemosensory, and respiratory structures. Avian bills should not be viewed as simply feeding structures, but rather as living structures, served by a network of nerves and blood vessels. As endotherms, birds also must contend with heat conservation in the cold and heat dissipation under warm conditions. As uninsulated structures, bills are therefore potential sites of significant heat exchange to and from their environment. We initially demonstrated the dramatic potential for heat exchange to the bill of the toco toucan. The toucan bill is well vascularised, and blood flow appears to be altered according to ambient temperatures or changes in internal heat loads. The capacity for heat loss is impressive, up to 4-5 times the rate of resting heat productions. We have also demonstrated that bill size is a thermally plastic trait in terms of developmental plasticity; larger bills will exchange heat more effectively through both surface area effects as well as changes to vascular conductance. Japanese quail reared in the cold show slower bill growth than birds reared at warm temperatures, and as adults are more effective at conserving heat loss from the bill, suggesting permanent alterations in the vasculature. This pattern of bill size-temperature dependency is a widespread evolutionary response. In over 200 species of non-migratory birds, we found strong evidence for smaller bill sizes in species living in cold environments, with the strongest relationships in avian families with the highest latitudinal ranges. Combined, the story emerging is that avian bills may be subject to selection by environmental temperatures, in addition to their functional role in feeding. Research funding provided to GJT by the Natural Sciences and Engineering Research Council of Canada and the National Geographic Society.

PHY1-3  3:00 pm  Mathematical models and bone histology shed light on maximal aerobic capacities of both extinct and extant tetrapods. Farmer CG*, University of Utah; Huttenlocker AK, University of Utah; Davis CL, Pepperdine University
Abstract: Our study aimed to test the hypothesis that there is a relationship between vascularity of musculoskeletal tissues, lung design, red blood cell (RBC) dimensions, and maximal rates of oxygen consumed during vigorous exercise in extant tetrapods. If such a relationship exists and its mechanistic basis is understood, it could be used to infer maximal aerobic capacities of extinct tetrapods. Maximal aerobic capacities are important in many ways. For example, they intertwine with mode of locomotion, they can determine the outcome of intraspecific competition and predator-prey interactions, and they are inversely correlated to genome size. We used mathematical models to understand the relationship between RBC dimensions, lung design, and oxygen uptake under different levels of inspired oxygen, and histology to study the link between RBC size and bone microvasculature in both extant and extinct lineages. Our models show that as levels of inspired oxygen decrease, maximal rates of oxygen uptake become increasingly sensitive to RBC size and hemoglobin concentration. In contrast, shifts of P50, for example by organic phosphates, had a very modest effect on oxygen uptake. We believe these results predict strong selection for reduced RBC size and thin blood gas barriers for highly active animals living in low oxygen conditions (e.g., in burrows, at altitude, during geologic periods of low environmental oxygen). Our histological analysis is the first to focus on the relationship between RBC dimensions and minimum canal caliber in cortical bone. Femora of several tetrapod species were sectioned at the midshaft and digitally imaged for histometric measurements and analysis. Multiple regression models support the hypothesis that minimum and harmonic mean canal caliber covary with RBC width and area. We use these results to retrodict the acquisition of mammal-like physiology in the synapsid lineage, focusing on Permo-Triassic therapsids. Supported by: NSF-BIO 1309040 to AKH and NSF-IOS-1055080 to CGF

PHY1-4  3:30 pm  Insular dwarfism and the distinct physiology in island deer: bone histology of Japanese extinct island cervids indicates interrupted growth. Hayashi S*, Osaka Museum of Natural History; Kubo M, The University of Tokyo; Fujita M, Okinawa Prefectural Museum & Art Museum; Taruno H, Osaka Museum of Natural History; Oshiro I, Okinawa-ishi-no-kai
Abstract: Miniaturization of island mammals is a well-known phenomenon in the evolutionary history of vertebrates, and therefore, a relationship between morphological reduction and physiological modification has been argued for. However, because of limited samples and a lack of ancestral taxa and/or kin, this relationship is still poorly understood. Here, we examine long bone histology of two extinct island cervids (Cervus astylodon and Muntiacini genus et sp. indet.) discovered from the Pleistocene deposits on Okinawa Island, Japan, to infer their life history and discuss their potential physiology in comparison to that of living relatives (C. nippon and Muntiacus reevesi). Bone histology of the two extinct island cervids is similar to each other and characterized by poorly vascularized parallel-fibered bone. Another peculiar characteristic of their histology are large amounts of lines of arrested growth (LAGs) with an external fundamental system (EFS), showing 13 LAGs with an EFS in C. astylodon and 6 LAGs with an EFS in Muntiacini gen. et sp. indet. The zones between LAGs are consistently narrow throughout the cortex, suggesting slow growth rates throughout life. In contrast to these island taxa, bone histology of the living relatives exhibits a highly vascularized fibro-lamellar bone and few LAGs with wider intervals throughout most of the cortex, agreeing with known observations of rapid body growth in the wild. Extinct island deer show distinctly slower growth and longer life histories compared to their living relatives. This life history strategy is similar to that typical for reptiles and an extinct island bovid, Myotragus; all having a low metabolic rate in common. Taken all together, dwarfism of C. astylodon and Muntiacini gen. et sp. indet. might be associated with a decrease in metabolic rate, and the extended life history could be due to a lack of predators on Okinawa Island until the invasion of humans in the Late Pleistocene.

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