Browsing by Author "Scott, Craig S."

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    An Analysis of North American Taeniolabidoid Multituberculate (Mammalia, Allotheria) Dentitions Using Mammalian Dietary Proxies
    (2018-12-20) Robson, Selina Viktoria; Theodor, Jessica M.; Scott, Craig S.; Cote, Susanne; Syme, Douglas A.; Zelenitsky, Darla K.
    In this thesis, a set of dietary proxies – dental microwear analysis, cusp row ratios (CRR) (similar to shearing ratios), relief index (RFI), orientation patch count rotated (OPCR), and Dirichlet normal energy (DNE) – was used to infer diets of North American taeniolabidoid multituberculates. Based on the signals recovered by these proxies, taeniolabidoid diets did not vary consistently with body size: small-bodied and large-bodied taeniolabidoids had similar dietary signals for almost all proxies, the only difference being in microwear feature dimensions. Dental microwear signals suggest that taeniolabidoids and non-taeniolabidoid cimolodontans may have had different diets, but all other proxies have recovered equivalent signals between the two groups. Dietary classifications are inconsistent among CRR, RFI, OPCR, and DNE. This suggests that these proxies are not equally good predictors and that their generalizability to non-therian mammals may need to be re-evaluated.
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    Lend Me Your Ear: Testing Hypotheses of Tylopod (Artiodactyla) Relationships Using Otic Region Morphology
    (2024-09-03) Robson, Selina Viktor; Theodor, Jessica Madeleine; Scott, Craig S.; Cote, Susanne Meredith; Summers, Mindi; Bertram, John Edward Arthur; Uhen, Mark D.
    Tylopoda are an artiodactyl suborder that includes camelids and their putative extinct relatives. A vast number of extinct species have been referred to Tylopoda, but the composition of the suborder remains unclear—few characters unite all purported tylopods, and those that do are ancestral features. Furthermore, the position of the suborder within Artiodactyla has recently come into question because of conflicting results from morphological and molecular phylogenetic analyses. Given that morphological and molecular data are unable to resolve these taxonomic problems, new lines of evidence are needed. The otic region, which includes the petrosal and bony labyrinth, is thought to be relatively slow-evolving, likely to retain phylogenetic characters important for resolving deep evolutionary relationships; these data have historically been inaccessible without destructive sampling, but with the proliferation of μCT scanning, the otic region is becoming increasingly easy to study. In this thesis, I describe the otic region of several early camelids and purported tylopods, including the dichobunoid Bunomeryx, two protoceratids, and two oromerycids. I used these data in conjunction with a larger unpublished dataset to code a taxon-character matrix primarily composed of otic region characters, which then analyzed with both parsimony and Bayesian analysis. All my analyses recovered a monophyletic Camelidae with Eotylopus, an oromerycid, the sister to Camelidae; I consider Tylopoda to include Camelidae and Oromerycidae. No other clade was consistently recovered with camelids, although oreodonts, anthracotheriids, and protoceratids all held that position in the results of some analyses. The placement of anthracotheriids was unexpected, but this appears to be the result of homoplasy; with additional dental, cranial, and postcranial characters, anthracotheriids are recovered sister to suoids. Based on my morphological descriptions and phylogenetic analyses, the otic region—particularly the petrosal—is not evolutionarily static. While the relative amount of homoplasy in the otic region compared to other skeletal regions was not tested, a large amount of intraspecific variation was observed in camelids, and all recovered (parsimony) topologies had a homoplasy index of over 0.70. This suggests that the petrosal is not as “slow evolving” as previously thought, an avenue of research that bears further investigation.