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Session Schedule & Abstracts
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|Friday 1st July, 2016|
|Moderator(s): Fortuny J, Hardin A|
LTG-1 2:30 pm Exploring integument mass properties in extant archosaurs and implications for digital volumetric modelling of centre of mass. Macaulay S*, University of Liverpool; Brophy P, University College Dublin; Allen V, Royal Veterinary College; Hone D, Queen Mary University of London; Bates K T, University of Liverpool; Hutchinson J R, Royal Veterinary College firstname.lastname@example.org |
Abstract: Feathers account for up to 16% of a bird’s total body mass, and play an essential role in flight for many avians. Despite this, integument data are yet to be rigorously incorporated into models exploring mass properties. Here, we report the first investigation and application of integument mass properties in sauropsids. In 29 specimens, sections of integument were excised encompassing key integument types (flight feathers, non-flight feathers and scaly skin), and major body segments. For each integument section, area, thickness and mass were measured, and density calculated. The density of all integument types correlated significantly with body mass, but our data also exhibit considerable scatter. When examined by body region, non-flight feather density showed non-significant differences. However, both scaly skin and flight feather density varied considerably. Some significant differences were found between feather types, likely a reflection of their different mechanical functions. Scaly skin density did not vary between birds, crocodilians and lizards. Flight feather density differed between major avian lineages, with hawks and moorhens at the extremes, potentially a result of distinct functional requirements (i.e. soaring vs. diving habits). Non-flight feather densities were similar across avian clades, with the exception of ostriches, the only flightless birds included here. Ostriches were also statistically distinct when density was assessed by locomotor type. Flight feather density showed differences between soaring birds and those favouring other flight modes. Application of our results to volumetric models of extant and extinct taxa enabled an examination of the effects of integument properties on whole-body mass properties. The consequences of this, and other common simplifications made around the application of densities to models are discussed, as well as their implications for the broader conclusions drawn from models, such as flight capabilities.
LTG-2 2:35 pm A survey of tooth character data amongst iguanian lizards reveals patterns related to size and taxonomy. Gray J A*, University of Adelaide; Hutchinson M N, South Australian Museum; Jones M E H, University of Adelaide email@example.com |
Abstract: Tooth number, size, and shape vary amongst fossil lizards and therefore have the potential to be used as taxonomically informative characters in the study of both living and fossil species. But for many taxa, data concerning the teeth remains limited, with basic data such as tooth number unreported for many, and published data is often based on a small sample of adult specimens. This knowledge gap brings into question the value of tooth data for interpreting fossils, particularly when fossils may not represent adult animals. The aim of this research is to assess whether data collected from teeth can be useful for identifying reptile fossils. The family Agamidae is one of many squamate clades for which we have not yet developed sets of dental and other osteological characters that would allow species-level identification. Using a sample of 596 extant iguanian skull specimens, including 322 agamids, we compiled a dataset of tooth characteristics including tooth number, size of the largest tooth, tooth row length, and basal skull length. Snout-vent length, sex, and age data were also available for some specimens. We investigated whether the data could be used for fossil identification. Clear differences exist between families of iguanian lizards. Discrimination between genera and species tends to be less obvious, but meaningful variation is still apparent across the sample. Some genera (e.g. Pogona) showed little difference amongst species, however others (e.g. Ctenophorus, showed some clear patterns potentially useful for fossil identification. A pilot study based on material from two Late Pleistocene locations in Southern Australia, finds that, when used in combination with other data such as other features of the maxilla, tooth number can meaningfully contribute to a confident identification for some Pleistocene fossil species.
LTG-3 2:40 pm Homologies in forelimb structure between moles and Early Paleogene insectivore mammals. Perepelova A.A.*, Zoological Institute RAS firstname.lastname@example.org |
Abstract: Fossil records of Didymoconida, the insectivore like mammals from Early Paleogene, are well known from the literature (Lopatin, 2006). Some scientists think they were good burrowers and that they lived in holes like moles. In our research we compared the forelimb structure of moles with that of Didymoconida and found some homologies in humerus morphology. In didymoconids as in moles humerus is widen, lateral and medial epicondyles are well developed. On the cranial side of the humerus in both forms there is a triangular fossa to which pectoral muscles attach. This space was supposed to be unique among moles for it corresponds to their empowered burrowing activity and is related with the transformation of ligamentum m. biceps brachii. In other mammals ligamentum m. biceps brachii lies in the intertubercular transverse, but in moles it changes direction. In semifossorial moles ligamentum m. biceps brachii runs along special ridge and in fossorial moles it is hidden inside the crest of lesser tubercle because the typical place for this ligament is filled by the increased pectoral muscles. In the humerus of Didymoconidae the similar patterns occur (in this group of mammals we can also find semifossorial and fossorial forms). Here we see a unique case of homology in forelimb structure between recent moles and extinct early Paleogene insectivore mammals. Special aspects of humerus structure can’t be considered as phylogenetic relationship between these two groups of mammals but perhaps they are connected with the similar type of locomotion.
LTG-4 2:45 pm Hunting in the Late Triassic: insights on the ambush strategy of the metoposaurs (Temnospondyli: Stereospondyli). Fortuny J.*, ICP - MNHN; Marcé-Nogué J., Centrum für Naturkunde - University of Hamburg; Konietzko-Meier D., Opole University email@example.com |
Abstract: The fluvial ecosystems of the Late Triassic were mainly dominated by different groups of early amphibians as capitosaurs and metoposaurs and archosaurs such as phytosaurs. The ecological niche of phytosaurs, with typical tubular-longirostral snout, clearly contrasts with the broad and flattened skulls found in capitosaurs and metoposaurs (e.g. Metoposaurus, Buettneria, Apachesaurus). The paleoecology of these early amphibians is still debated, with capitosaurs usually considered as active top predators with an amphibious mode of life. The paleoecology of metoposaurs is less understood. Some of its members presented a tendency to gigantism and characterized by huge thickness of skull bones. Metoposaurs were aquatic and potentially burrowing animals, with adaptations to burying during dry seasons. However, no study focused in the feeding ecology and biomechanical capabilities of these animals. Herein, we analyzed two metoposaur taxa—Metoposaurus krasiejownsis and Apachesaurus gregorii, from Europe and North America respectively—using Finite Element Analysis (FEA). Two adult skulls were CT-scanned and 3D models were analyzed under different biomechanical scenarios including bilateral, unilateral and lateral biting, as well as skull raising system, under different gapes. Stresses are specially found in posterior part of the skull, in agreement with higher thickness of the bones, providing support to stress constraints. Considering the palate, the results reflects the importance of the cultriform process, well developed in metoposaurs, in the functional stability of the skull. Our results confirm that these animals were ambusher predators, resting on the floor and waiting for preys as previously suggested. Of particular interest, our results reveal that these animals were specialized feeders, using only a rapid bilateral biting, clearly avoiding other biomechanical behaviors such as rapid lateral strike of the head or unilateral biting.
LTG-5 2:50 pm Genome assembly and annotation of Mastomys coucha, a murid with an extreme mammary phenotype. Hardin A*, University of California, San Francisco; Carbone L, Oregon Health & Science University; Ahituv N, University of California, San Francisco firstname.lastname@example.org |
Abstract: Mammary glands are the latest in a series of derived ectodermal involutions that include teeth, hair and sweat glands. They are located on the surface of the body in a tightly regulated and repetitive manner. There is a large variation in mammary gland numbers between mammals in general and in rodents in particular with numbers ranging from two to twelve pairs. The Southern multimammate mouse, Mastomys coucha, has evolved a total of twelve pairs of mammary glands since the 8MYA divergence from Mus and can be used to contrast with the more typical five and six pairs present in Mus and Rattus respectively. To better understand the molecular determinants that lead to mammary gland number diversity, we sequenced and assembled a draft genome of M. coucha. Our genome is at an estimated depth of 75x with an N50 of over 100kb. We identified 67% of conserved eukaryotic genes and 83% of mouse genes in our assembly. Importantly, we identified homologs of 81% of mouse genes expressed in the E12.5 mammary bud. Further comparative genomic analyses and functional genomics will examine M. coucha for differential gene expression at key mammary gland developmental time points and diverged gene regulatory regions around these genes. Combined, our analyses show that the draft genome of M. coucha is a valuable resource for questions of rodent phenotypic diversity.
LTG-6 2:55 pm Body shape vs. osteology in the fish superfamily Cottoidea. Buser TJ*, Oregon State University; Summers AP, University of Washington email@example.com |
Abstract: Sculpins are a speciose and morphologically diverse group of fishes found in diverse habitats across the northern hemisphere. The morphological diversity of sculpins, especially of the North American species of the genus Cottus, is broad and has led to confusion. Within this widespread genus, there can be a confounding overlap in many commonly used morphological characters (i.e., fin rays, mandibular pores, etc.), and substantial morphological phenotypic plasticity within a given species. We are using X-ray micro-tomography (µCT) to determine the extent to which changes in the morphology of specific bones correlate with changes in aspects of body shape across the diversity of sculpin species. We are finding differences in osteology that ultimately result in a superficially indistinguishable phenotype. This could lay the framework for a better understanding of not only the evolution and radiation of sculpins, but perhaps more practically, more concrete and precise delimitation of some of the sculpin species, particularly in the genus Cottus. The use of µCT in this study allows us to reconstruct and quantitatively compare minute structures in three dimensions across large numbers of individuals with high precision. As we catalog morphological diversity and generate hypotheses of the evolutionary history of sculpins, we are making the µCT data available as an open resource freely available via the Open Science Framework website (https://osf.io/) so any researcher can download and analyze scans as they are completed.
LTG-7 3:00 pm Physical properties of the sub-dermal fibrous layers in cetacean tail flukes. Gough WT*, West Chester University; Fish FE, West Chester University; Bart-Smith H, University of Virginia firstname.lastname@example.org |
Abstract: During swimming, cetaceans generate hydrodynamic thrust with dorso-ventral oscillations of flexible tail flukes. These flukes do not contain rigid skeletal structures. Instead, they are mainly comprised of densely packed collagenous fibers that are arranged into two distinct layers. Flukes from common dolphins (Delphinus delphis), bottlenose dolphins (Tursiops truncatus), harbour porpoises (Phocoena phocoena), and pygmy sperm whales (Kogia breviceps) were dissected out to compare the morphology of the two fibrous layers. In all species, the fibers of the ligamentous layer (outer layer) were angled with respect to the spanwise axis of the fluke. The core layer (inner layer) of all species was found to contain fibers angled with respect to the chordwise axis, while the core layer of the pygmy sperm whales was found to contain additional fibers embedded throughout the layer that were angled along the spanwise axis. Compression tests were performed on the core layer fibers of harbour porpoises and pygmy sperm whales at multiple locations along the span of each fluke. Greater compressibility was found along the chordwise axis than along the spanwise axis at all locations for both species. The two-dimensional orientation of the core layer fibers was determined using a stereomicroscope under polarized light. Fibers in the core layer in the parasagittal plane displayed a crisscrossing arrangement with fibers oriented at an average of either 66° or 115° in relation to the chord line. In all species, the arrangement and orientation of the fibers within the fibrous layers impart anisotropic properties to the flukes and help them to maintain their shape and flexibility during swimming.
LTG-8 3:05 pm Seasonal skin anatomy changes in three sympatric anuran species from the Midwestern United States. VanBuren C S*, University of Cambridge email@example.com |
Abstract: Vertebrates have evolved multiple strategies to cope with high seasonality and avoid unfavorable conditions (e.g., hibernation and migration). In some anuran species, skin anatomy has been observed to differ seasonally; for example thicker during dry or winter seasons, thinner in the wet or summer seasons. This suggests that anurans modify epidermal anatomy to acclimate to high seasonality. However, studies regarding this variation have only compared skin thickness between generalized seasons, so the timing and drivers of this anatomical change are unclear. I used museum collections to sample three sympatric anuran species native to the Midwestern United States, the American bullfrog, the Northern leopard frog, and the spring peeper, across multiple months to 1) confirm seasonal-related differences in skin anatomy and 2) elucidate the timing of these anatomical changes on a finer scale. Skin samples were taken from the dorsal, ventral, and thigh regions and prepared using standard histological techniques. Epidermis thickness was averaged from 10 measurements for each region. Snout-vent length (SVL) was used to account for body size. Epidermis thickness, standardized by SVL, was then plotted against the month the specimen was collected. The analyses found that spring peepers follow previously predicted patterns by having thinner skin in the summer months compared to the spring and fall. However, bullfrogs and leopard frogs increase skin thickness near the end of summer, reaching greatest skin thickness in September or October before then thinning the skin again. Together, these results suggest that seasonal changes in anuran skin anatomy are more complex than previously recognised and may be related to differential overwintering behavior or shared evolutionary history among these species.
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