Megalocnus

''Megalocnus'' ("great sloth" in Greek) is a genus of extinct large ground sloths that were native to Cuba during the Pleistocene and Holocene epochs. They were among the largest of the Caribbean sloths (Megalocnidae), with individuals estimated to have weighed up to 270 kg (595 lbs) to 200 kg (440 lbs), around the size of a black bear when alive.Steadman, D. W., Martin, P. S., MacPhee, R. D., Jull, A. T., McDonald, H. G., Woods, C. A., ... & Hodgins, G. W. (2005). Asynchronous extinction of late Quaternary sloths on continents and islands. ''Proceedings of the National Academy of Sciences'', ''102''(33), 11763-11768. Its relatives include other megalocnid sloths, such as '' Acratocnus'', '' Mesocnus'', '' Miocnus'', '' Neocnus and'' '' Parocnus''. The former species ''M. zile'' from Hispaniola is currently thought to be a junior synonym of ''Parocnus serus''.

Etymology

''Megalocnus'', the generic name, means "great sloth" after the similarities between the holotype's caniniformes with modern sloth's, while ''rodens'' means "rodent-like" due to the original misidentification of the fossils as those of a rodent.Leidy, J. (1868). Notice of some vertebrate remains from the West Indian islands. ''Proceedings of the Academy of Natural Sciences of Philadelphia'', 178-180.

History and taxonomy

''Megalocnus'' was first described based on an incomplete mandible first described by "D. M. F. de Castro", collected by him in April, 1860 in Pleistocene deposits of the thermal springs in Arriete-Ciego Montero in what is now Cienfuegos Province, Cuba, though the fossil now apparently is held in the Museo Nacional de Ciencias Naturales. It was first identified as the mandible of a large rodent due to the erosion on the canines. The mandible was then given to Prof. Felipe Poey of Havanna, who described it briefly in 1861. The fossil wasn't named until 1868 when American paleontologist Joseph Leidy he described it as a new species of the large ''Megalonyx'', ''Megalonyx rodens,'' though stated that it could be a different genus, which he erected as ''Megalocnus.'' A few months later, Parisian naturalist Pomel was sent the fossil by Poey for the 1867 Parisian exposition, who named it as ''Myomorphus cubensis'', subgenus of ''Megalonyx''. Despite this, ''Megalocnus rodens'' has priority. In the coming years, more fossil sloths would be named from the Caribbean based on fossils from Puerto Rico and Hispaniola, but it wasn't until the 1910s that a large quantity of fossils of ''Megalocnus'' were found. The American Museum of Natural History and the notable Cuban scientist Dr. Carlos de la Torre y Huerta collected dozens of fossils of many partial skeletons from 1910 to 1918 at Arriete-Ciego Montero, which resulted in the discovery of enough fossils to mount 3 different skeletons for the AMNH, though only 2 are mounted today at the AMNH, and a skeleton for the Cuban Museum of Natural History. Dr. de la Torre was apparently so fond of his mounted skeleton that he would exhibit it at nearly every exhibition he could. However, one of the skeletons mounted at the AMNH has since been revealed to bear the right femur of the closely related '' Parocnus browni.'' The fossils would be described in detail by both AMNH and Cuban staff over the next 50 years.Couto, C. D. P. (1967). Pleistocene edentates of the West Indies. American Museum novitates; no. 2304.

In 1979, a scapula and several other ''Megalocnus'' fossils were collected by C. A. Woods & co. from Quaternary deposits in Trou Gallery, Ile de la Tortue in the Departement du Nord-Oues, Haiti. These were the first fossils of ''Megalocnus'' outside of Cuba described, and were named in 2000 as a new species, ''Megalocnus zile''. However, the species has since been synonymized witn '' Parocnus serus.''McAfee, R. K., & Beery, S. M. (2019). Intraspecific variation of Megalonychid sloths from Hispaniola and the taxonomic implications. ''Historical Biology''.

Fossil history

Subfossils of ''M. rodens'' indicate survival well into the Holocene. The most recent AMS radiocarbon date reported is 4190 BP, calibrated to c. 4700 BP. This is similar to the most recent date reported for a Hispaniolan sloth, 4391 BP, calibrated to c. 5000 BP, for the small and probably semiarboreal '' Neocnus comes'', and some 1,200 years after the earliest known date for human occupation of Cuba, 5140 BP, calibrated to c. 5900 BP.

Description and paleobiology

Due to the large sample size of fossils and the number of well preserved skeletons of ''Megalocnus'', the anatomy of the genus is well known, although the taxon has yet to receive any recent research. Of the Caribbean Megalocnids, ''Megalocnus'' was the largest and most abundant, with estimates placing it at up to 270 kg (595 lbs) to 200 kg (440 lbs). ''Megalocnus'' largely differs from ''Hapalops'' in skull and dental structure, especially in the orientation of the enlarged anterior teeth, and has a heavier body with a broader rib cage, more widely flaring ilium, and more elongate ungual phalanges.Coombs, M. C. (1983). Large mammalian clawed herbivores: a comparative study. ''Transactions of the American Philosophical Society'', ''73''(7), 1-96. The larger size, relatively shorter tibia, broader rib cage, flared ilia, and other characters of ''Megalocnus'' may suggest more terrestrial habits than those of ''Hapalops'' or '' Acratocnus''. The limbs of ''Megalocnus'' were low crural, again suggesting that ecologically ''Megalocnus'' was a terrestrial, ground feeding fossil sloth rather than a tree climbing one.

Some paleontologists historically have proposed splitting ''M. rodens'' into several different species and subspecies, those being ''Megalocnus rodens rodens, M. r. casimbae,'' & ''M. ursulus,'' though this may just be individual variation. ''M. r. casimbae'' was diagnosed by Couto (1967) as; incisiform teeth about two-thirds as wide as those of ''M. rodens rodens''; M2-4 intermediate between those of this species and those of ''M. ursulus''. ''M. ursulus'' was diagnosed by; size about two-thirds of that of ''M. rodens,'' convexity of mandible beneath and behind last molar much less. Molar teeth less broad. M3 possibly one-sixth wider than long. ''M. ursulus'' may just be a young ''M. rodens rodens'', as pointed out by Couto.

Gallery

Megalocnus.jpg, ''M. rodens'' at Cuban Academy of Sciences, Havana, early 1900s
Megalocnus rodens in Havanna Museum of Natural History.jpg, ''M. rodens'' at Cuban Museum of Natural History, 2018
Megalocnus rodens skull.jpg, Partial ''M. rodens'' skull
Ground sloths.jpg, Partial view of AMNH mount in left foreground

See also

* Pilosans of the Caribbean

References

External links

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{{Taxonbar, from=Q141383

Prehistoric sloths
Prehistoric placental genera
Pleistocene xenarthrans
Pleistocene first appearances
Holocene extinctions
Pleistocene mammals of North America
Extinct animals of Cuba
Mammals of Hispaniola
Extinct animals of the Dominican Republic
Extinct animals of Haiti
Fossils of Cuba
Mammals of Cuba
Mammals of the Caribbean
category:Mammals of the Dominican Republic
category:Mammals of Haiti
Fossil taxa described in 1868
Taxa named by Joseph Leidy