The hindlimb of Amphicynodon leptorhynchus from the lower Oligocene of the Quercy Phosphorites (France): Highlight of new climbing adaptations of this early arctoid

An exquisitely preserved skeleton of Eoarctos vorax (nov. gen. et sp.) from Fitterer Ranch, North Dakota (early Oligocene) and systematics and phylogeny of North American early arctoids (Carnivora, Caniformia)

“…Fdml for USNM 637259 is 7.8 mm (average for left and right femora), and the estimated body mass for Eoarctos is 4.3 kg. Such a body mass falls within range of a modern fisher ( Pekania pennanti , 3.5–5.5 kg) (Powell, 1981) or tayra ( Eira barbara , 2.7–7 kg) (Presley, 2000), but slightly smaller than that of a modern raccoon ( Procyon lotor , 5.9–6.7 kg from Missouri) (Lotze and Anderson, 1979) and somewhat larger than the European early arctoid Amphicynodon leptorhynchus (1.94 kg) (Gardin et al, 2021, 2022).…”

“…Abundant evidence throughout its skeleton suggests a scansorial mode of locomotion. The entire appendicular skeletons of Eoarctos and Amphicynodon (Gardin et al, 2021, 2022) show numerous differences from canids and clearly are not cursorial in their locomotion. Most of the limb joints suggest a lack of restricted movements along parasagittal planes seen in pure cursors, permitting wide-ranging rotations at various joints.…”

“…In an unpublished Ph.D. dissertation, Cirot (1992) figured a nearly complete skeleton of Amphicynodon leptorhynchus from the Itardies fissure fill in the classic Quercy Phosphorites localities of southern France with an estimated age of MP23 in the early Oligocene (Legendre et al, 1997). This skeleton, partially published by Gardin et al (2021Gardin et al ( , 2022, was partly articulated (although each bone was given separate catalog numbers) and associated with both jaws. Such a specimen with secure taxonomic assignment is rare and valuable because many classic Quercy collections may have well-preserved individual postcranial bones but are mostly represented by isolated specimens that lack a clear association with dental material.…”

“…Nonetheless, Eoarctos retains enough plesiomorphic features of early, arboreal carnivorans, such as a full-length clavicle and a deep claw (terminal phalanx), that it was probably still quite capable of climbing trees, at least for escape. Gardin et al (2021Gardin et al ( , 2022 envisioned a primarily arboreal locomotion for the European Amphicynodon leptorhynchus but a form still capable of foraging on the ground. We note, however, that the skeleton of Amphicynodon is largely comparable to that of Eoarctos but is perhaps slightly more terrestrial in its overall morphology than in Eoarctos (i.e., Eoarctos retains slightly more plesiomorphic limb features).…”