Phylogenetic Assessment of the Genus Steinius (Euprimates; Omomyidae)

The genus Steinius has been determined to be one of the earliest forms of omomyids after being hypothesized to belong in the earliest anaptomorphines dating back to the Eocene. This genus is thought to be one of the ancestors of later omomyids. Other ancestors would include an early omomyid with characteristics resembling the primitive characteristics of Steinius. There are two sister taxa belonging to this genus, Steinius annectens and Steinius vespertinus. Both taxa appear within the strata at Bighorn Basin in Wyoming, with S. annectens appearing in early forms of stratigraphy compared to S. vespertinus. Specimens of both taxa are also lacking with only jaw fragments and single teeth specimens being known today. Although much of Steinius is unknown, it can be associated with Tarsiiformes, or tarsiers. The specimens in this study consisted of lower jaw fragments that were assessed via a microscope containing a reticle calibrated for tooth measurements. These measurements and visual assessments could be used later in the study to determine the relatedness of both taxa. This thesis provides an assessment on the dental morphological characteristics of the genus Steinius that includes both qualitative and quantitative data. The relationship between both sister taxa of this genus is also discussed in detail with a comparison of the similarities found in both teeth. The results obtained from this evaluation showed that both taxa can be determined to be related. One key difference that was noted, however, is that S. annectens has an average tooth size that is larger than that of S. vespertinus and other early omomyids.