Oldest well‐preserved euprimate petrosal, from the early Eocene of India (Vastan Lignite Mine, Gujarat)

An exquisitely preserved, isolated partial petrosal with associated fragmentary stapes is described from the Vastan Lignite Mine (Gujarat, India), dated to the early Eocene (~54.5 Ma). Several anatomical traits (e.g., large petrosal plate; posterolateral entry of the internal carotid artery to the tympanic cavity; bony tubes surrounding the internal carotid artery and stapedial artery) allow the specimen to be confidently allocated to Euprimates, making it likely the oldest and among the best-preserved petrosals known for this clade. Of the two superfamilies of primates known from Vastan Mine-Adapoidea and Omomyoidea-the anatomy of the petrosal is more consistent with an attribution to Adapoidea (e.g., epitympanic crest present, no bony tube surrounding the promontorial artery). Body mass estimation indicates that the petrosal came from a small species (≤186 g), suggesting it most likely pertains to the asiadapid Marcgodinotius indicus, the smaller of the two named adapoids known from the Vastan fauna. Locomotor reconstructions based on semicircular canal radii of curvature and inter-canal angles are incongruent, with the former being more consistent with postcranial interpretations of the asiadapids as relatively cautiously moving taxa without specializations for leaping, while the latter suggests a more active form of locomotion. The specimen exhibits traits inferred to be primitive (e.g., lack of a bony tube for promontorial artery, shallow epitympanic recess, short cochlea), which are consistent with the idea that Asiadapidae constitutes a very early branch of the adapoid tree. Indeed, this specimen is similar to what might be expected for a basal strepsirrhine.