Cimolestes

Cimolestes; Temporal range: Late Campanian-Latest Thanetian; ~75–56 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Lower jaw (LACM 152546) of C. stirtoni, Natural History Museum of Los Angeles County
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	†Cimolesta
Family:	†Cimolestidae; Marsh, 1889
Genus:	†Cimolestes; Marsh, 1889
Type species
	†Cimolestes incisus; Marsh, 1889
Synonyms
	Nyssodon Simpson, 1927

Cimolestes (from Ancient Greek Κιμο λέστες, 'chalk robber')^[1] is a genus of early eutherians with a full complement of teeth adapted for eating insects and other small animals. Paleontologists have disagreed on its relationship to other mammals, in part because quite different animals were assigned to the genus, making Cimolestes a grade taxon of animals with similar features rather than a genus of closely related ones. Fossils have been found in North America, South America, Europe and Africa. Cimolestes first appeared during the Late Cretaceous of North America. According to some paleontologists, Cimolestes died out at the start of the Paleocene,^[2] while others report the genus from the early Eocene.^[3]

Most species have been described from teeth and isolated fragments. One complete articulated skeleton provisionally assigned to Cimolestes has been found. It shows a small, agile, tree-dwelling predator with long toes for grasping branches and a prehensile tail at least twice the length of its body. It has the largest number of tail vertebrae known in any mammal.^[3]

Classification

The genus was once considered to be that of a marsupial; later, it was reclassified with the placental mammals, as ancestors of the Carnivora and the extinct Creodonta. Recent researchers have agreed the species assigned to Cimolestes are primitive eutherian mammals, members of a cimolestid clade (an order or family named after the genus), part of the larger clade Didelphodonta (a superorder or order, not to be confused with the marsupial clade Didelphimorphia). Didelphodonts have been placed within the Ferae, as a sister group to Carnivora. However, consensus is emerging that modern placental mammals evolved later than previously thought,^[4]^[5] that other types of mammals had long, diversified, and successful histories, and that Cimolestes and many related genera are stem eutherians, more closely related to placentals than to marsupials but outside of placental mammals proper, and not closely related to any living animal.^[6]

Cimolestes in particular follows as the direct outgroup to Taeniodonta, indicating that the latter evolved from forms similar to it.^[6]

Reassigned species

In order to make the genus reflect an actual group of most closely related species, three nominal species of Cimolestes, C. magnus, C. cerberoides, and C. propalaeoryctes, have been reassigned to their own genera, Altacreodus, Ambilestes, and Scollardius, respectively. Cimolestes incisus (Marsh) and Cimolestes stirtoni (Clemens) remain within the genus.^[7]

Fossil distribution

Fossils of Cimolestes have been found in:^[8]

Cretaceous

Canada
- Foremost, Oldman and St. Mary River Formations, Alberta
- Ravenscrag and Frenchman Formations, Saskatchewan
United States
- Hell Creek and Judith River Formations, Montana
- Kirtland Formation, New Mexico
- Lance Formation, Wyoming

Paleocene

Hainin Formation, Belgium
Santa Lucía Formation (Tiupampan), Bolivia
Ravenscrag and Frenchman Formations, Saskatchewan, Canada
Jbel Guersif Formation, Morocco
United States (Puercan)
- Bear and Hell Creek Formations, Montana
- Ferris Formation, Wyoming

Eocene

Fossil Butte Member, Green River Formation, Wyoming, United States^[3]

References

^ "Cimolestes". p. 189. in Palmer, T. S. (23 January 1904). "Index Generum Mammalium: A List of the Genera and Families of Mammals". North American Fauna. 23: 1–984. doi:10.3996/nafa.23.0001.
^ McKenna, M. C.; S. K. Bell (1997). Classification of Mammals Above the Species Level. Columbia University Press. ISBN 978-0-231-11012-9.
^ ^a ^b ^c Grande, Lance (2013). The Lost World of Fossil Lake; Snapshots from Deep Time. Chicago: University of Chicago Press. pp. 260–263. ISBN 978-0-226-92296-6.
^ O'Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; Gaudin, Timothy J.; Giallombardo, Andres; Giannini, Norberto P.; Goldberg, Suzann L.; Kraatz, Brian P.; Luo, Zhe-Xi; Meng, Jin; Ni, Xijun; Novacek, Michael J.; Perini, Fernando A.; Randall, Zachary S.; Rougier, Guillermo W.; Sargis, Eric J.; Silcox, Mary T.; Simmons, Nancy B.; Spaulding, Michelle; Velazco, Paúl M.; Weksler, Marcelo; Wible, John R.; Cirranello, Andrea L. (2013). "The Placental Mammal Ancestor and the Post—K-Pg Radiation of Placentals". Science. 339 (6120): 662–667. Bibcode:2013Sci...339..662O. doi:10.1126/science.1229237. hdl:11336/7302. JSTOR 23365914. OCLC 827160921. PMID 23393258. S2CID 206544776.
^ O'Leary, Maureen A. (2014). "On the Trail of the First Placental Mammals". American Scientist. 102 (3): 190–197. JSTOR 43707184. Gale A370031758 ProQuest 1522775462.
^ ^a ^b Rook, D.L.; Hunter, J.P. (2013). "Rooting Around the Eutherian Family Tree: the Origin and Relations of the Taeniodonta". Journal of Mammalian Evolution. 21: 1–17. doi:10.1007/s10914-013-9230-9. S2CID 17074668.
^ Fox, Richard C. (December 2015). "A revision of the Late Cretaceous–Paleocene eutherian mammal Cimolestes Marsh, 1889". Canadian Journal of Earth Sciences. 52 (12): 1137–1149. Bibcode:2015CaJES..52.1137F. doi:10.1139/cjes-2015-0113.
^ Cimolestes at Fossilworks.org

[1] "Cimolestes". p. 189. in Palmer, T. S. (23 January 1904). "Index Generum Mammalium: A List of the Genera and Families of Mammals". North American Fauna. 23: 1–984. doi:10.3996/nafa.23.0001.

[McK&B-2] McKenna, M. C.; S. K. Bell (1997). Classification of Mammals Above the Species Level. Columbia University Press. ISBN 978-0-231-11012-9.

[:0-3] Grande, Lance (2013). The Lost World of Fossil Lake; Snapshots from Deep Time. Chicago: University of Chicago Press. pp. 260–263. ISBN 978-0-226-92296-6.

[4] O'Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; Gaudin, Timothy J.; Giallombardo, Andres; Giannini, Norberto P.; Goldberg, Suzann L.; Kraatz, Brian P.; Luo, Zhe-Xi; Meng, Jin; Ni, Xijun; Novacek, Michael J.; Perini, Fernando A.; Randall, Zachary S.; Rougier, Guillermo W.; Sargis, Eric J.; Silcox, Mary T.; Simmons, Nancy B.; Spaulding, Michelle; Velazco, Paúl M.; Weksler, Marcelo; Wible, John R.; Cirranello, Andrea L. (2013). "The Placental Mammal Ancestor and the Post—K-Pg Radiation of Placentals". Science. 339 (6120): 662–667. Bibcode:2013Sci...339..662O. doi:10.1126/science.1229237. hdl:11336/7302. JSTOR 23365914. OCLC 827160921. PMID 23393258. S2CID 206544776.

[5] O'Leary, Maureen A. (2014). "On the Trail of the First Placental Mammals". American Scientist. 102 (3): 190–197. JSTOR 43707184. Gale A370031758 ProQuest 1522775462.

[rook-6] Rook, D.L.; Hunter, J.P. (2013). "Rooting Around the Eutherian Family Tree: the Origin and Relations of the Taeniodonta". Journal of Mammalian Evolution. 21: 1–17. doi:10.1007/s10914-013-9230-9. S2CID 17074668.

[7] Fox, Richard C. (December 2015). "A revision of the Late Cretaceous–Paleocene eutherian mammal Cimolestes Marsh, 1889". Canadian Journal of Earth Sciences. 52 (12): 1137–1149. Bibcode:2015CaJES..52.1137F. doi:10.1139/cjes-2015-0113.

[8] Cimolestes at Fossilworks.org

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