Jeholodens jenkinsi (Ji et al. 1999; Middle Cretaceous) was a sister to Spinolestes (above) within the Tritylodontidae in the large reptile tree.
Ji et al. 1999 reported, "The postcranial skeleton of this new triconodont shows a mosaic of characters, including a primitive pelvic girdle and hindlimb but a very derived pectoral girdle that is closely comparable to those of derived therians. Given the basal position of this taxon in mammalian phylogeny, its derived pectoral girdle indicates that homoplasies (similarities resulting from independent evolution among unrelated lineages) are as common in the postcranial skeleton as they are in the skull and dentition in the evolution of Mesozoic mammals."
From the Ji et al. 1999 paper (Fig. 3) it looks like Jeholodens has a basal tarsus because distal tarsal 4 is not wide enough to double as a distal tarsal 5, as it does in the marsupial, Didelphis. A quick peek at Rattus (Fig. 4), Vulpavus and Onychonycteris shows that these placental taxa likewise do not widen distal tarsal 4 to back up pedal digit 5. Comparable pedes among other tritylodontids are hard to find. |
