It is time to take a dive into more very scarcely understood “rodents” of Eocene China, to actually see how they might have looked like when they were still alive.
The monophyly of the cohort Glires, has been disputed for many years. In the present, new genetic studies confirm the monophyly between the two orders, rodents and lagomorphs. Glires however, includes many ancestral, primitive and basal forms that cannot be stricly defined as a rodent or a lagomorph. Glires can be actually better divided to duplicidentata and simplicidentata. Duplicidentates (two tooth) includes the lagomorphs and other closely related forms (with two pair of front incisors) that are not part of the crown group lagomorpha. The same applies for simplicidentata (one tooth), Rodents and their closely allied forms. Inside simplicidentata, another order sister to Rodentia was established to lump some non-rodent simplicidentates called Mixodonta.
One monotypic genus of one of these obscure basal gliroids is Rhombomylus turpanensis. It is known from a lot of different specimens, also from different stages of ontogenic development. Its anatomy is derived to a certain extend, more so, than that of its very close relative Matutinia nitidilus, which possesses more primitive dentition and skull, and it is also smaller in size.
Here is my musculoskeletal reconstruction of the anatomy of Rhombomylus turpanensis. The postrcranial anatomy of this species remains largely obscure. It was likely an unspecialized terrestrial, non-cursorial form with some capabilities for jumping. The hindlimbs are much longer than the forelimbs.
And the life reconstruction:
Here is my another reconstruction of a close relative of Rhombomylus of a different genus, Matutinia nitidilus. I see these animals resembling perhaps the living pikas (Ochotonidae) or the mountain beaver (Aplodontia rufa) and perhaps also the true rats (Rattus). Terrestrial herbivores, living in burrows and dens. They would also supply their diet with animal protein if given the change. These are my guesses of what would be their best modern analogue, althought their trophic ecology did not had to be exactly identical to the before-mentioned examples.
Basal gliroids and their closely related clades remain largely obscure. I hope more research will continue on this group to shed some light on these creatures.
References:
- SUYIN TING, JIN MENG, MALCOLM C. McKENNA, and CHUANKUEI LI “The Osteology of Matutinia(Simplicidentata, Mammalia) and Its Relationship to Rhombomylus,” American Museum Novitates2002(3371), 1-33, (21 June 2002). https://doi.org/10.1206/0003-0082(2002)371<0001:TOOMSM>2.0.CO;2
- JIN MENG, YAOMING HU, and CHUANKUI LI “THE OSTEOLOGY OF RHOMBOMYLUS (MAMMALIA, GLIRES): IMPLICATIONS FOR PHYLOGENY AND EVOLUTION OF GLIRES,” Bulletin of the American Museum of Natural History 2003(275), 1-247, (28 February 2003). https://doi.org/10.1206/0003-0090(2003)275<0001:TOORMG>2.0.CO;2
