Notostylops

Notostylops; Temporal range: Early-Late Eocene (Casamayoran-Divisaderan); ~48.6–37.2 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Notostylops
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	†Notoungulata
Family:	†Notostylopidae
Genus:	†Notostylops; Ameghino, 1897
Species
	N. murinus (type species) Ameghino, 1897; N. appressus (Ameghino, 1902); N. pendens (Ameghino, 1901); N. pigafettai Simpson, 1948;
Synonyms
	Anastylops Ameghino, 1897; Catastylops Ameghino, 1901; Entelostylops Ameghino, 1901; Eostylops Ameghino, 1901; Isostylops Ameghino, 1902; Pliostylops Ameghino, 1901;

Notostylops ("south pillar face") is a genus of extinct South American notoungulates from Eocene Argentina. Fossils of the genus have been found in the Sarmiento, Casamayor, Andesitas Huancache and Koluel Kaike Formations.^[1]

Size comparison of Notostylops murinus with a human.
Life reconstruction.

Description

Notostylops was a very generalised animal, very similar to the first eutherians and ungulates. It would have superficially resembled a marmot or a wombat and is suspected to have browsed on low-growing plants. It was probably adapted to a fairly wide range of ecological niches, but its robustness indicates it had some digging adaptations.^[2]^[3] Its tall skull housed rodent-like incisor teeth. Notostylops incisors lacked complex, decussating enamel prisms, instead possessing radial enamel.^[4] The endocast of N. murinus had a volume of 9,807 mm³, with the volume of the olfactory bulbs being 629 mm³. Notostylops had a degree of cranial flexure of 34˚.^[5] Notostylops was about 75 centimetres (30 in) long.^[6]

References

^ Notostylops at Fossilworks.org
^ Croft, Darin. Horned Armadillos and Rafting Monkeys. Indiana University Press.
^ Lorente, Malena; Gelfo, Javier; Lopez, Guillermo (2018). "First skeleton of the notoungulate mammal Notostylops murinus and palaeobiology of Eocene Notostylopidae". Lethaia. 52 (2): 244–259. doi:10.1111/let.12310. S2CID 135127572.
^ Filippo, Andréa; Kalthoff, Daniela C.; Billet, Guillaume; Gomes Rodrigues, Helder (13 March 2019). "Evolutionary and Functional Implications of Incisor Enamel Microstructure Diversity in Notoungulata (Placentalia, Mammalia)". Journal of Mammalian Evolution. 27 (2): 211–236. doi:10.1007/s10914-019-09462-z. ISSN 1064-7554. Retrieved 31 October 2025 – via Springer Nature Link.
^ Perini, Fernando A.; Macrini, Thomas E.; Flynn, John J.; Bamba, Kanvaly; Ni, Xijun; Croft, Darin A.; Wyss, André R. (23 November 2021). "Comparative Endocranial Anatomy, Encephalization, and Phylogeny of Notoungulata (Placentalia, Mammalia)". Journal of Mammalian Evolution. 29 (2): 369–394. doi:10.1007/s10914-021-09583-4. ISSN 1064-7554. Retrieved 17 January 2026 – via Springer Nature Link.
^ Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 250. ISBN 978-1-84028-152-1.