Data from: Morphology of the petrosal and stapes of Borealestes (Mammaliaformes, Docodonta) from the Middle Jurassic of Skye, Scotland

\We describe, in unprecedented detail, the petrosals and stapes of the
docodont Borealestes from the Middle Jurassic of Scotland, using high
resolution μCT and phase‐contrast synchrotron imaging. We describe the
inner ear endocast and the vascularized interior structure of the
petrosal, and provide the first endocranial view of a docodontan petrosal.
Our study confirms some similarities in petrosal and stapedial morphology
with the better known Haldanodon of the Late Jurassic of Portugal,
including: (1) the degree of curvature of the cochlea; (2) multiple
features related to the highly pneumatized paroccipital region; (3) the
shape of lateral trough, the fossa of the M. tensor tympani, and the ridge
on the promontorium; (4) the round shape of the fenestra vestibuli; and
(5) overall morphology of the stapes. But Borealestes differs from
Haldanodon in having a bony ridge that separates the tympanic opening of
the prootic canal, the secondary facial foramen and the hiatus Fallopii,
from the fenestra vestibuli. We identify two new vascular structures: the
anterior and posterior trans‐cochlear sinuses, which traverse the pars
cochlearis around the cochlear nerve (VIII). These trans‐cochlear sinuses
have not been observed in previous docodont specimens, and could be an
autapomorphy of Borealestes, or apomorphic for this clade. We also
establish the anatomical relationship of the circum‐promontorium plexus to
the inner endocast. The high quality of our scans has made these
structures visible for the first time.