Data from: Whence the beardogs? Reappraisal of the Middle to Late Eocene ‘Miacis’ from Texas, USA, and the origin of Amphicyonidae (Mammalia, Carnivora)

The Middle to Late Eocene sediments of Texas have yielded a wealth of
fossil material that offers a rare window on a diverse and highly endemic
mammalian fauna from that time in the southern part of North America.
These faunal data are particularly significant because the narrative of
mammalian evolution in the Paleogene of North America has traditionally
been dominated by taxa that are known from higher latitudes, primarily in
the Rocky Mountain and northern Great Plains regions. Here we report on
the affinities of two peculiar carnivoraforms from the Chambers Tuff of
Trans-Pecos, Texas, that were first described 30 years ago as Miacis
cognitus and M. australis. Re-examination of previously described
specimens and their inclusion in a cladistic analysis revealed the two
taxa to be diminutive basal amphicyonids; as such, they are assigned to
new genera Gustafsonia and Angelarctocyon, respectively. These two taxa
fill in some of the morphological gaps between the earliest-known
amphicyonid genus, Daphoenus, and other Middle-Eocene carnivoraforms, and
lend additional support for a basal caniform position of the beardogs
outside the Canoidea. The amphicyonid lineage had evidently given rise to
at least five rather distinct forms by the end of the Middle Eocene. Their
precise geographical origin remains uncertain, but it is plausible that
southern North America served as an important stage for a very early phase
of amphicyonid radiation.