Typotheria

Typotheria Temporal range: Late Paleocene–Pleistocene PreꞒ Ꞓ O S D C P T J K Pg N
Mesotherium
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	† Notoungulata
Suborder:	† Typotheria Zittel, 1892
Families
Archaeohyracidae Archaeopithecidae Campanorcidae Hegetotheriidae Interatheriidae Mesotheriidae Notopithecidae Oldfieldthomasiidae

Typotheria is a suborder of the extinct South American native ungulate order Notoungulata. A majority of the members of this clade were superficially similar to lagomorphs and rodents, though this is due to convergence.

Anatomy

Typotheres all possess a clavicle, unlike other notoungulates in Toxodontia. They have narrow phalanges (the bones of the digits) and claw-like nails. Most typotheres had additional auditory chambers, much like the toxodonts. ^[1] The cheek teeth and incisors tend to be hypsodont, meaning that they bore high crowns, which is indicative that many typotheres ate a diet of tough plants. ^[2] The dental canal leads to a branch which comes from the mandibular ramus, posteriorly (towards the rear) and on the outer side. ^[3]

Diversity

Typotheres were at their most diverse in the early Oligocene, with many of the families of the group having large radiations. Hegetotheriids in particular were incredibly well represented in many formations, with multiple different sequential dispersion events occurring. Mesotheriids, and in particular Mesotherium , persisted into the Pleistocene. ^[4]

Depiction by Charles R. Knight of Pachyrukhos , a hegetotheriid typothere

Classification

There has been debate over where Typotheria places amongst notoungulates. Some literature places them within Toxodontia, ^[1] but more recent literature places them as sister clades. The placement of Hegetotheriidae in Typotheria has been contested in the past, with the original description proposing they converged on a similar skull structure to the other typotheres, and that Typotheria and Hegetotheriidae were sister clades. ^[5] This is not supported, however, by modern phylogenies. ^{[4] [2]}

References

1. Scott, William Berryman; Scott, William Berryman (1913). A history of land mammals in the Western Hemisphere; illustrated with 32 plates and more than 100 drawings. New York: Macmillan.
2. Reguero, Marcelo; Prevosti, Francisco (2010). "Rodent-like notoungulates (Typotheria) from Gran Barranca, Chubut Province, Argentina: phylogeny and systematics" (PDF). Cambridge University Press: 149, 156 – via Cambridge.
3. Cope, Edward (1897). "Toxodontia". The American Naturalist. 31 (366): 490. doi:10.1086/276634 – via University of Chicago Press Journals.
4. Cerdeño, Esperanza; Juñent, Sergio Roig; Seoane, Federico D (2017). "Phylogeny and paleobiogeography of Hegetotheriidae (Mammalia, Notoungulata)". Journal of Vertebrate Paleontology: 5 – via Talor and Francis Group.
5. Ameghino, Florentino (1889). Contribucion al conocimiento de los mamiferos fosiles de la República Argentina: Obra escrita bajo los auspicios de la Academia nacional de ciencias de la República Argentina para ser presentada á la Exposicion universal de Paris de 1889 (in Spanish). P. E. Coni é hijos.