Protungulatum

Protungulatum ('first ungulate') is an extinct genus of eutherian mammals within extinct family Protungulatidae,^[1] and is possibly one of the earliest known placental mammals in the fossil record, that lived in North America from the Late Cretaceous to early Paleocene.^[6][3][7]

Protungulatum Temporal range: 66.3–63.8 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ late Maastrichtian to Puercan
lower jaw of Protungulatum donnae
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Grandorder:	Ferungulata
Clade:	Pan-Euungulata
Family:	†Protungulatidae Chatterjee, Scotese & Bajpai, 2017[1]
Genus:	†Protungulatum Sloan & Van Valen, 1965[2]
Type species
†Protungulatum donnae Sloan & Van Valen, 1965
Species
†P. coombsi (Archibald, Zhang, Harper & Cifelli, 2011)[3] †P. donnae (Sloan & Van Valen, 1965) †P. gorgun (Van Valen, 1978)[4] †P. mckeeveri (Archibald, 1982)[5] †P. sloani (Van Valen, 1978)

Fossils of this genus were first found in the Bug Creek Anthills in northeastern Montana. The Bug Creek Anthills were initially believed to be Late Cretaceous (latest Maastrichtian) because of the presence of the remains of non-avian dinosaurs and common Cretaceous mammals,^[8] but these were later shown to have been reworked^[a] from Late Cretaceous strata, and consequently the Bug Creek Anthills are currently believed to be Early Paleocene (Puercan) in age.^[9] Remains from the Ravenscrag Formation of Saskatchewan, Canada have been assigned to Protungulatum donnae. These remains may also be Cretaceous in age, but the age of the Ravenscrag Formation is not entirely certain. In 2011, a new species Protungulatum coombsi was named based on fossil material discovered from the strata within the Hell Creek Formation specifically dated to at least 300,000 years before the K-Pg extinction, suggested that Protungulatum was present in both the latest Cretaceous and the early Paleocene. P. coombsi was estimated to be 20% larger than the next largest Paleocene species.^[3]

Studies differ on the placement of Protungulatum. This genus was initially assigned to the family Arctocyonidae,^[10] in order Condylarthra,^[11][12] (a group of archaic "ungulates", that is now known to be polyphyletic). Some found that it is not a true placental mammal and it is eutherian found to be close to Placentalia.^{[13][3][14][15]} However, a number of studies consider it to be a placental mammal and stem relative to true ungulates in clade Pan-Euungulata,^{[16][17][18][19][7][20][21][22]} based on anatomy of inner ear.^[7]

Speculative life reconstruction

Phylogeny

The phylogenetic relationships of genus Protungulatum are shown in the following cladogram.^[16][19]

Scrotifera	Apo-Chiroptera †"Wyonycteris" microtis †Eosoricodontidae †Acmeodon †Gelastops Ferungulata Ferae Pan-Euungulata Euungulata (sensu stricto) †Protungulatidae †Protungulatum †Protungulatum coombsi †Protungulatum gorgun †Protungulatum donnae †Protungulatum mckeeveri †Protungulatum sloani ? †Protungulatum sp. (PTRM 1277) (Euungulata [sensu lato])

Notes

1. A derived or reworked fossil is a fossil found in rock made significantly later than when the fossilized animal or plant died: it happens when a hard fossil is freed from a soft rock formation by erosion and redeposited in a currently forming sedimentary deposit.