Data from: A lower jaw of Palaeoxonodon from the Middle Jurassic of the Isle of Skye, Scotland, sheds new light on the diversity of British stem therians

The Middle Jurassic was a key interval of mammalian evolutionary history
that witnessed the diversification of the therian stem-group. Great
Britain has yielded a significant record of mammalian fossils from this
interval, represented by numerous isolated jaws and teeth from the
Bathonian of Oxfordshire and the Isle of Skye. This record captures a key
period in early cladotherian evolution, with amphitheriids, peramurans and
“stem zatherians” displaying intermediate talonid morphologies that
document the evolutionary assembly of tribosphenic molars. We present a
mandible with near-complete dentition from the late Bathonian (ca.
167.4–166.5 Ma) Kilmaluag Formation, near Elgol, Skye, representing the
amphitheriid Palaeoxonodon ooliticus, previously known only from isolated
teeth. The specimen sheds new light on the taxonomic diversity of British
Middle Jurassic stem therians, as the morphological variation within the
preserved tooth row encompasses that previously ascribed to three distinct
species within two genera: Palaeoxonodon ooliticus, P. freemani, and
Kennetheridium leesi. Thus, both P. freemani and Kennetheridium leesi are
subjective junior synonyms of P. ooliticus. The dental formula of P.
ooliticus (i4:c1:p5:m5) is intermediate between the primitively larger
postcanine count (p5:m6-7) of Amphitherium and the reduced number in
peramurans and tribosphenidans (p5:m3). Phylogenetic analyses of P.
ooliticus generally confirm a close affinity with Amphitherium, but
highlight the lack of strong empirical support for hypothesized patterns
of divergences among early cladotherians.