Browsing by Author "Robson, Selina Viktor"

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    A reassessment of protoceratid vertebrarterial canal morphology
    (Taylor and Francis, 2022-08-31) Robson, Selina Viktor; Theodor, Jessica M.
    The Protoceratidae are a family of extinct artiodactyls that have been variably allied with camelids and ruminants. One of the few synapomorphies uniting protoceratids and camelids is their unusual vertebrarterial canal morphology; the canal passes through the cervical vertebrae at an oblique angle rather than through the bases of the transverse processes. This unusual morphology has been upheld as a key piece of evidence for a close relationship between the two families. Upon reviewing the literature and examining specimens of three protoceratid genera, we have determined that protoceratids do not share a vertebrarterial canal morphology with camelids. Indeed, the vertebrarterial canal of protoceratids passes through the bases of the transverse processes, the condition found in most artiodactyls. This eliminates the only synapomorphy uniting protoceratids and camelids and leaves the phylogenetic position of protoceratids ambiguous.
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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.