I present another short post and reconstruction of another not very well-known prehistoric tooth-digging rodent, of Early Oligocene.

So, here we have it, Tsaganomys altaicus. It belonged to the family Tsaganomyidae, comprising 3 genera and 5 species. Tsaganomys was native to Oligocene and possible early Miocene of Asia. It possesed a protrogomorphous zygomasseteric system (the most primitive type found in rodents) of the skull and a hystricomorphous mandible. It had massively developed almost circular zygomatic arches, large temporal fossa, prominent sagittal and occipital crests, hypsodont (high crowned) dentition and of course, procumbent incisors, among other traits.

The phylogenetic position and ancestry of tsaganomyids appears to be unresolved. Due to several superficial similarities, tsaganomyids were associated with bathyergids, cylindrodonts and hystricognaths. Now it’s clear that this group is not closely related to any of the before mentioned clades. For example, the bones of the middle ear, malleus and incus are not fused as in Bathyergidae, or for example the incisor microstructure is quite different from that of the cylindrodonts. Also, they lack other derived features common for hystricognaths. For now, tsaganomyids shall remain Rodentia incertae sedis.

For more detailed description, I highly suggest reading the original paper I referenced (under the drawing).

Here is my reconstruction of Tsaganomys altaicus. Missing postcranial proportions are based off of Bathyergus and soft tissues are based off of several different species of zokors (Myospalacinae).

References:

On Tsaganomyidae (Rodentia, Mammalia) of Asia (Banyue Wang, 2001) https://doi.org/10.1206/0003-0082(2001)317%3C0001:OTRMOA%3E2.0.CO;2