| Propachyrucos | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | †Notoungulata |
| Family: | †Hegetotheriidae |
| Genus: | †Propachyrucos Ameghino, 1897 |
| Species: | †P. smithwoodwardi |
| Binomial name | |
| †Propachyrucos smithwoodwardi Ameghino, 1897 | |
Propachyrucos is anextinctgenus of late Oligocenehegetotheriid notoungulate. It is known from a few mandibular fragments from theSarmiento Formation,Chubut Province,Argentina.[1]
Propachyrucos may have been similar to the rabbit-sizedProsotherium, but was almost 20% smaller, more similar in size toPachyrukhos andPaedotherium, and almost 30% larger thanTremacyllus.[1]
The molars had two internal folds separated by a further deep fold, like theInteratheriidae ; dentalcementum was present, but to a lesser extent than inInteratherium. The lower teeth were flat on the outside and bilobed on the inside.[citation needed]
Propachyrucos was first described in 1897 byFlorentino Ameghino, based on a right mandible fragment found inOligocene terrains of theSarmiento Formation inArgentina, initially believed by Ameghino to have beenCretaceous. The type species isPropachyrucos smithwoodwardi, but other species have been attributed to the genus, such asP. aequilatus,P. robustus, andP. ameghinorum, the latter species, described in 1945 byGeorge Gaylord Simpson from fossils found in theChubut Province, is known from a remarkably complete skeleton, permitting to reconstruct the animal appearance with high precision. However, recent researches tend to indicate that all the other species ofPropachyrucos are in fact synonymous with the type species.[2]
Propachyrucos was ahegetothere, a group of notoungulates that evolved in isolation on the South American continent, giving rise to forms resemblinghares andrabbits.Propachyrucos was a member ofPachyrukhinae, a subfamily of hegetotheres particularly similar to modernlagomorphs.
In a 1999 unpublished Ph.D. dissertation, thePropachyrucos speciesP. ameghinorum andP. simpsoni were synonymized withProsotherium garzoni. This was supported by a 2019 reassessment as well as a number of other studies. As the most well preserved specimen ofPropachyrucos was previously the nearly completeholotype ofP. ameghinorum,Propachyrucos smithwoodwardi is now only known from a few mandibular fragments. The 2019 study recovers the features ofP. ameghinorum as consistent with those of juvenileProsotherium garzoni (although the holotype ofP. ameghinorum was not directly examined). Despite this, until 2019, phylogenetic analyses regularly scoredPropachyrucos for cranial and post-cranial characters, which are known only from the synonymizedP. ameghinorum andP. simpsoni.[1]
Propachyrucos and its relatives were animals well suited to running and jumping. Body proportions similar to those ofPropachyrucos's relatives can also be found in theCainotheriidae, a group ofartiodactyls from theOligocene-Miocene ofEurope.[1]
