Leptocyon mollis (Merriam), 1906

TEDFORD R. H., WANG X. & TAYLOR B. E., 2009, Phylogenetic Systematics Of The North American Fossil Caninae (Carnivora: Canidae), Bulletin of the American Museum of Natural History 2009 (325), pp. 1-218 : 18

Leptocyon mollis (Merriam), 1906 Figures 3, 5, 6H–J; appendices 2, 3

Nothocyon geismarianus mollis Merriam, 1906: 13 , pl. 2, fig. 1 and pl. 3, fig. 1.

Type: UCMP 90 ( AMNH 129683 , cast; fig. 6H–J), skull with I3 broken–C, P1 broken, and P2–M2 from the Turtle Cover Member of the John Day Formation , Turtle Cove , John Day River , Grant County, Oregon. This unit spans ca. 29–30 Ma ( Fremd et al., 1994), early Arikareean .

Revised Diagnosis: L. mollis differs from L. douglassi in its larger size and proportionally larger M1 and M2 (fig. 5); from L. vulpinus it differs in its smaller and lower crowned premolars; from L. gregorii it differs in its wider palate, backward direct- ed, more robust, and salient paroccipital process, in larger and lower crowned P3, in more robust P4 with relatively larger and more anteriorly situated protocone and proportionally larger M1 with more prom- inent cingulum and slightly stronger parastyle, and in proportionally larger M2 that bears a metaconule.

Description and Comparison: The holotype skull was designated a race of Nothocyon geismarianus by Merriam (1906: 13 compared with the referred skull, AMNH 6885, now the holotype of Cormocyon copei Wang and Tedford, 1992 ). He stated: ‘‘Except for the somewhat smaller size, lyrate arrangement of the temporal ridges and somewhat narrower molars, this form is close to N. geismarianus ’’ ( Merriam, 1906: 13). For the reasons cited by Merriam, the skull is excluded from Cormocyon copei , assigned to the genus Leptocyon , and raised to specific rank.

Although the dentition of the type skull is smaller than that of Leptocyon vulpinus , the relatively large and broad molars recall those of the latter, rather than the smaller molars of L. gregorii . Relatively large molars and a strong M1 parastyle are also characters that distinguish L. vulpinus from L. gregorii .

Unfortunately, no skull of L. vulpinus is known, but L. mollis can be compared with the incomplete type skull ( AMNH 12872) of L. gregorii (see proportional comparison in fig. 3). The type skulls of L. mollis and L. gregorii are approximately equal in size and proportionally similar except for the broader palate and relatively larger M 2 in L. mollis . The lyrate temporal ridges of L. mollis are more widely separated than in other early species of Leptocyon and resemble some examples of Hesperocyon . Although more laterally expanded (slightly emphasized by dorsoventral crushing), the cranium of L. mollis is elongate as in L. gregorii , with the cerebellar exposure similar to that of the latter. Both have tiny postparietal foramina. The morphology of the paroccipital process in this taxon is the most primitive known among the Caninae . Its base is broadly connected to the bulla, but it retains a robust and salient process that is more posteriorly directed than in other species of Leptocyon .

When the worn dentition of the type of L. mollis is compared with that of L. gregorii , the P3 is slightly larger and lower crowned in L. mollis and the strong posterior crest has a very weakly differentiated cuspule. More- over, the P4 is more robust in L. mollis (fig. 5) with a relatively larger and more anteriorly situated protocone. Allowing for wear, the molars of L. mollis are relatively larger. The M1 appears to have almost subequal paracone and metacone with a more prominent buccal cingulum and a stronger parastyle than that of the type of L. gregorii . L. mollis further differs from the latter in its proportionally smaller and lower crowned premolars.