Miacis gracilis, a new carnivore from the Uinta Eocene

Abstract

Annalsof the Carnegie Museum vol. xxvii Specific characters: taken only from the type. The characters of the referred specimen will be noted in the discussion.(1) Differs from M. parvivorus in having the paraconid of M 2 low, relative to the protoconid, and having no cingular cuspule, while in M. parvivorus the paraconid is high, and the cingulum anterior to the protoconid is drawn into a tiny cuspule.( 2 ) Differs from M. medius in that the C, M^, and M^ are almost twice as large in M. medius as in M. gracilis, although the cheek-tooth rows are about of the same length. M^ and M^ of M. medius are sharply cusped, while in M. gracilis the cusps are low, almost extinct. M^ of M. medius has a broad external cingular table at the posteroexternal corner of the tooth, while the cingulum is close to the metacone in M. gracilis.(3) Differs from M. latidens in having the cingulum of M^ close to the metacone, and the cingulum prominent and continuous internally while in M. latidens there is a broad postero-external table and the internal cingulum is low and discontinuous. Also, M^ of M. latidens is almost as broad transversely as is M^, while in M. gracilis, M^ is markedly reduced. M 2 of M. latidens is somewhat larger than M 2 of M. gracilis, and M 3 is twice as large as the corresponding tooth in M. gracilis.(4) The chief differences between M. exiguus and M. gracilis are proportional. Total length of the lower cheek-tooth dentition in M. exiguus is less than ^ that in M. gracilis, while M 2 of M. exiguus is almost as large, and M 3 fully as large, as the corresponding teeth in M. gracilis.(5) The referred specimen of M. sylvestris in the American Museum (A.M.N.H. no. 13071), has the molars approximately half as large as the corresponding teeth in M. gracilis. I have not had the opportunity to make a direct comparison with the type in this case.( 6 ) The type of M. washakius has the broad postero-external cingular table on M\ which occurs also in M. medius and M. latidens, and is not present in M. gracilis. Also, M^ of M. washakius is extremely short antero-posteriorly, and very low-crowned, while in M. gracilis it is longer and higher crowned.(7) In the fragmentary type of Mimocyon longipes Peterson, sometimes referred to Miacis, each bone is almost exactly twice as large as the corresponding bone in M. gracilis. In the absence of good characters for comparison in Mimocyon longipes, this seems a valid basis for a specific distinction between the two.( 8 ) The type of Prodaphoenus (?) rohustus Peterson, referred by Hay^ to Miacis, is twice as large as M. gracilis, and has a heavy mandible with a distinct chin, while in M. gracilis the mandible is slender and tapering.

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)

“…The cranial (external) surface of the patella is also relatively smooth, lacking longitudinal striations seen in larger carnivorans. The overall shape and proportions are quite similar to that of Miacis gracilis (Clark, 1939:pl. XXXVI).…”

“…In cranial view, the olecranon process has a strong tilt toward the medial side. The proximal surface of the olecranon lacks a distinct notch seen in canids, a condition also present in Miacis gracilis (Clark, 1939:pl. XXXV, fig.…”

“…This remnant wingtip suggests that the wings are thin-bladed and not rod-like as in many musteloids. Clark (1939) figured the only known atlas from the miacoid species Miacis gracilis , which is similar to that of Eoarctos .…”

“…Postcranial skeletons from early miacoids are generally rare and only a handful of papers provide some illustrations. Clark (1939) described a partial skeleton of Miacis gracilis , and Heinrich and Rose (1995) described a partial skeleton of Miacis petilus . For more early forms, Heinrich and Houde (2006) illustrated limbs of Viverravus , whereas Spaulding and Flynn (2009) provided descriptions of “ Miacis ” uintensis .…”

“…On the ventral side, two distinct ridge-like processes immediately caudal to the condyles are visible. In Miacis gracilis (Clark, 1939:pl. XXXVI), the proximal phalanx is more dorsally arched than that in Eoarctos , and such an arch may be a sign for grasping of tree branches in arboreal life.…”