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Moropus; Temporal range: Early-Middle Miocene, 20.43–13.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Moropus elatus skeleton at the; National Museum of Natural History,; Washington, DC
	Reconstruction of the head of M.elatus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	†Chalicotheriidae
Subfamily:	†Schizotheriinae
Genus:	†Moropus; Marsh, 1877
Species
	M. distans Marsh, 1877; M. elatus Marsh, 1877; M. hollandi Peterson, 1907; M. matthewi Holland & Peterson, 1913; M. merriami Peterson, 1914; M. oregonensis Leidy, 1873; M. senex Marsh, 1877;

Moropus (meaning "slow foot") is an extinct genus of large perissodactyl ("odd-toed" ungulate) mammal in the chalicothere family. They were endemic to North America during the Miocene from ~20.4–13.6 Mya, existing for approximately 6.8 million years. Moropus belonged to the schizotheriine subfamily of chalicotheres, and has the best fossil record of any member of this group; numbers of individuals, including complete skeletons, have been found.

The closest extant relatives of Moropus are other perissodactyls: horses, rhinos, and tapirs.^[2]

Description

Like other chalicotheres, Moropus differed from typical ungulates in having large claws, rather than hooves, on the feet.^[2] Three large, highly compressed claws were present on each of the front feet, supported inside by fissured bony phalanges. In a classic example of convergent evolution, Moropus and its kin developed feet which were structured quite similarly to those of the extinct giant ground sloths (such as Megatherium), their giant claws and ‘hands’ being a formidable defense against predators. The feet also (likely) featured similar qualities and functions to today’s extant Xenarthra—a unique group of animals containing the giant and silky anteaters, armadillos, the tamandua and the two- and three-toed sloths. The name Moropus translates to "slow (or sloth) foot", implying it was a clumsy mover. However, as with all schizotheriines, the articulation of the phalangeal (finger) bones shows that Moropus could retract the claws enough to walk smoothly with the front feet in a normal digitigrade stance, lifting the claws by hyperextension of the phalangeal hook.^[3]

Moropus was one of the largest chalicotheres,^[4] standing about 2.4 metres (8 ft) tall at the shoulder.^[5] Like other schizotheriines, the teeth were adapted to browsing, and the narrow skull with high nasal bones comes to a spoon-shaped tip, a characteristic common to leaf-eating mammals that browse selectively, grasping their food with mobile lips and a long tongue. The pelvis and hindlimbs would have allowed living individuals to rear up on their hind legs, using the front claws to hook tree branches and pull them within reach of the lips and tongue. Measurements of multiple individuals in at least one species (M. elatus) suggest there was sexual dimorphism, with one sex larger than the other.^[6]

Moropus was an uncommon animal in the woodland and savanna environments where it lived. However, at the Agate Springs bonebed in Nebraska, the remains of seventeen individuals were found in a thirty-six foot area, which suggests that in at least some situations Moropus came together in groups.^[7] The front and back legs of this genus were more similar in length than most advanced chalicotheres, which may indicate it was better adapted to life in more open environments, spending less time standing at trees and more time walking and running.^[8]

Fossil distribution

Phillips Ranch, Kern County, California estimated age: ~18.7 Mya.
Stewart Spring (UCMP 2027), Mineral County and Esmeralda County, Nevada estimated age: ~18.7 Mya.
Stage Hill I, aka Millennium's End Quarry, Scotts Bluff County, Nebraska estimated age: ~21.6—21.5 Mya.
Sucker Creek site, Sucker Creek Formation, Malheur County, Oregon ~16.4 Mya.
Anderson Ranch Formation, Agate Fossil Beds National Monument, Nebraska estimated age ~ 21.3-19.2 Mya.

Species distributions

M. elatus - Colorado, Nebraska
M. hollandi - Wyoming, Nebraska
M. merriami - Nevada, Nebraska
M. oregonensis - Oregon, Texas, Florida

References

^ "Moropus in the Paleobiology Database". Fossilworks. Retrieved 17 December 2021.
^ ^a ^b Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 261. ISBN 1-84028-152-9.
^ Coombs, Margery Chalifoux (1983). "Large Mammalian Clawed Herbivores: A Comparative Study". Transactions of the American Philosophical Society. 73 (7): 1–96. doi:10.2307/3137420. ISSN 0065-9746. JSTOR 3137420.
^ Patricia Vickers Rich, Thomas Hewitt Rich, Mildred Adams Fenton, Carroll Lane (January 15, 2020). The Fossil Book: A Record of Prehistoric Life. Dover Publications. p. 573. ISBN 9780486838557. Retrieved 2022-08-25.{{cite book}}: CS1 maint: multiple names: authors list (link)
^ Agate Fossils National Monument NPS Natural Resource Report NPS/NRPC/GRD/NRR-2009/080 (J. Graham, March 2009)
^ Coombs, Margery Chalifoux (1973). Front cover image for The Schizotheriinae (Mammalia, Perissodactyla, Chalicotheriidae), with emphasis on the genus Moropus (Thesis). OCLC 1090678060.
^ Osborn, Henry Fairfield (July 1919). "Seventeen Skeletons of Moropus; Probable Habits of this Animal". Proceedings of the National Academy of Sciences. 5 (7): 250–252. Bibcode:1919PNAS....5..250F. doi:10.1073/pnas.5.7.250. PMC 1091586. PMID 16576385.
^ Holland, W. J.; Peterson, Olof August (1914). The osteology of the Chalicotheroidea. OCLC 906224063.^{[page needed]}