| Coloniatherium | |
|---|---|
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Clade: | †Meridiolestida |
| Family: | †Mesungulatidae |
| Genus: | †Coloniatherium Rougieret al., 2009 |
| Species: | †C. cilinskii |
| Binomial name | |
| †Coloniatherium cilinskii Rougieret al., 2009 | |
Coloniatherium is ameridiolestid mammal from theLate Cretaceous ofArgentina. The single species,Coloniatherium cilinskii, was a large member of the familyMesungulatidae.
Coloniatherium was named in 2009 byGuillermo Rougier and colleagues and assigned to the familyMesungulatidae within theDryolestoidea.[1] Dryolestoidea is an extinct mammalian group that occurred in North America, Eurasia, and Africa during theJurassic andEarly Cretaceous, but survived in South America during theLate Cretaceous and into thePaleocene.[2] Thegeneric name,Coloniatherium, combines the name of theLa Colonia Formation, the stratigraphical unit where fossils of the animal were found, and its namesake theSierra de La Colonia with the Greektherion "beast". Thespecific name,cilinskii, honors Juan Cilinski, a local rancher who helped with the fieldwork that led to the discovery ofColoniatherium.[1]
Coloniatherium is known from a few jaw fragments, a number of isolated teeth,[1] and somepetrosals (ear bones).[3] It was a large mesungulatid.[1] The animal had an unknown number ofincisors (probably two or three in the lower jaw),[3] onecanine, threepremolars, and threemolars per jaw quadrant.[1] It is larger thanMesungulatum, has broader molars, and the back molars are more reduced; the two also differ in numerous details of tooth morphology.[3] The first molar has three roots, a trait shared only withLeonardus from the approximately contemporaneousLos Alamitos Formation of Argentina among dryolestoids.[4]
The petrosal ofColoniatherium appears to be similar in terms ofphylogenetic position toVincelestes, an Early Cretaceous Argentinean mammal, but also share some apparentlyderived traits withtherians (i.e.,marsupials,placentals, and relatives).[5] Based on comparisons withVincelestes, the length of the skull ofColoniatherium would be estimated to be 87.5 mm (3.4 in); comparisons with therians suggest a larger skull length, but the former estimate is more in line with the size of the jaws.[6] It is estimated to weigh ~3.69 kg.[7]
Fossils ofColoniatherium come from the La Colonia Formation, which outcrops in north-centralChubut Province. The mammalian fossils come from theMirasol Chico valley. The formation includes fluvial (river), deep-sea, and near-shore deposits, and the mammalian fauna probably comes from an estuary, tidal flat, or coastal plain.[1] La Colonia Formation also contains dryolestoids, such asColoniatherium andReigitherium, as well as the enigmatic possible multituberculatesArgentodites andFerugliotherium.[8]Coloniatherium is the largest and most abundant mammal found in the formation.[1]
Mesungulatids, includingColoniatherium, are a highly derived group of mammals, possibly specialized for anomnivorous toherbivorous diet,Coloniatherium cilinskii's large population density possibly indicating the latter as it is among the most common vertebrates in its faunal assemblage.[9][10] They are among the most distinctive products of the unique Mesozoic radiation of South American mammals.[11]
