Similar to other borophagines, Tomarctus had a short, robust skull. The muzzle especially was short and broad, though not as broad as the related Borophagus. The saggital and lambdoidal crests of Tomarctus are enlarged, indicating strong jaw muscles. The teeth are highly specialized for crushing and shearing, with the teeth and dentary portion of the mandible being robust.[1] A widened forehead and more complex sinus morphology can distinguish Tomarctus from Protomarctus.[2] The premolars are enlarged. Endocranial casts of Tomarctus have been found, with the inferred shape of the brain being similar to modern canids.[3]
Reconstruction of Tomarctus brevirostris
Postcrania
The forelimbs of Tomarctus are robust, and not adapted for pursuing prey quickly. The humerus has deep olecranon fossae (pits on the posterior end of the humerus), as well as an entepicondylar foramen, a trait lost in the later borophagines. The ulna is broad, and the radius has a distinct process on the anterior surface. The tibia of Tomarctus lacks muscular grooves. The middle phalanx is short and the claw is more elongate than those of related borophagines. Tomarctus was likely digitigrade, unlike more primitive canids.[4]
The genus currently contains two accepted species, Tomarctus brevirostris and Tomarctus hippophaga. Historically, the genus has had more species assigned to it, though the validity of those species is questioned. Tomarctus is considered a basal borophagine and is grouped closest with Aelurodon.[2]
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