Abstract
ABSTRACT Bunomeryx is an early North American artiodactyl commonly thought to be an ancestral tylopod. Much of the evidence for this relationship comes from the otic region. We can now elaborate on this evidence by using computed tomography scanning to reconstruct previously undescribed parts of the Bunomeryx otic region, including the bony labyrinth. Furthermore, a great deal of research has been conducted on artiodactyl petrosals since the petrosal of Bunomeryx was first described, providing an opportunity to compare this potentially pivotal taxon to other early artiodactyls and the early camelid Poebrotherium, a definitive tylopod. Our comparisons have revealed a need to update three anatomical terms: the subarcuate fossa, the mastoid fossa, and the ventromedial flange. We provide revised definitions along with morphological descriptions. Based on our comparisons, the otic region of Bunomeryx is broadly similar to most early artiodactyls, with the greatest similarity to Homacodon, another early North American artiodactyl. Many features thought to unite Bunomeryx with Tylopoda, such as a large subarcuate fossa, are widespread in these early taxa. Others, such as a ventromedial flange and an anteromedial tuberosity, may have evolved multiple times. The presence of a small, triangular internal acoustic meatus may link Bunomeryx to later branching tylopods such as Poebrotherium, but this morphology is also present in Homacodon. It appears that, rather than Bunomeryx having a derived tylopod morphology, camelids possess some plesiomorphic and potentially convergent characters. Bunomeryx may be an ancestral tylopod, but there is less evidence for this relationship than previously thought.
Published Version
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