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Wednesday, 24 October 2012

Tetrapod Zoo on Sloths

I am reprinting part of this article of Darren Naish's because people don't realise what a diversity of sloths there once were and why we are facing a quandry when we are talking about the possibility of surviving groundsloths. We do not only have survivals of one kind of generic groundsloth that is reported everywhere today, but instead we have a number of reports of highly varied groundsloths with different anatomies described in different areas. And I thought I sould mention that my home manuscript report dealing with the topic has a drawing basically like a simplified version of Darrens drawing for "Sloth Diversity" shown directly below.-DD

The anatomy of sloths

By Darren Naish August 30, 2012 About Darren Naish Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. He has been blogging at Tetrapod Zoology since 2006.  Darren Naish is a vertebrate palaeontologist, currently based at the University of Southampton, UK. From 1997 to 2006 I worked on the predatory dinosaurs of the Lower Cretaceous of southern England, focusing for my PhD on the tyrannosauroid Eotyrannus. My published technical work is mostly on theropod and sauropod dinosaurs, but I've also worked on pterosaurs, marine reptiles and marine mammals (see list of references below). Since completing my PhD I’ve worked in the media and as a technical editor and freelance author (see list of books below). I like dinosaurs very much, but they’re far from the only animals that I find interesting: I'm fascinated by all tetrapods and have some practical and research experience with Mesozoic marine reptiles, marine mammals, flightless birds and pterosaurs. I spend as much time in the field as possible, looking at real live tetrapods.

Everybody loves sloths, and whenever we talk about sloths we have to remember that the two living kinds (Bradypus – the four species of three-toed sloth – and Choloepus – the two species of two-toed sloth) are but the tip of the iceberg when it comes to sloth diversity. This article – an excerpt from Naish (2005) (though with citations added that were absent in the published article) – briefly reviews the anatomy of fossil sloths, though there are references to the living forms where appropriate.

A typical fossil sloth can be imagined as a rather bear-shaped, shaggy-furred mammal with particularly powerful forelimbs, a barrel-shaped ribcage, a stout tail, prominent curved hand and foot claws and a markedly broad, robust pelvis.

Skulls from various sloths. a. Eremotherium, a Pleistocene megatheriid known from both South and North America. b. Nematherium, a mylodontid from Early Miocene South America. c. Scelidotherium, a scelidotheriine mylodontid from the Pliocene and Pleistocene of South America. d. Thalassocnus, a nothrotheriid from the Miocene and Pliocene of the Pacific coast of South America. e. Acratocnus odontrigonus, a choloepodine megalonychid from the Pleistocene of Puerto Rico. f. Acratocnus simorhynchus, an even shorter-snout choloepodine, from the Pleistocene of Hispaniola. Not to scale. Images by Darren Naish, redrawn from various sources. From Naish (2005).
Naish, D. 2005. Fossils explained 51: sloths. Geology Today 21 (6), 232-238.
--Now the problem we have with groundsloths as live candidates for reported Cryptids is that the reported ones are seldom a very good match: in discussing the reprinting of this article, Darren Naish mentions that proponents "cherry pick" traits which they choose to make out as important correspondences between the reports which they have and the fossil candidates they wish to promote. Now a severe problem in this category is the identification of the legendary Mapinguary or Mapinguary of South America, commonly represented in Cryptozoological literature as being a type of surviving giant ground sloth, probably a type of Mylodon. In this case the fossil candidate fails on two important counts: the legendary creatures are not supposed to have tails and they are supposed to have fightening fangs in the mouth. This rules out the Mylodons because the Mylodons were quite lacking in foreteeth. Farther north in the Caribbean reports of hairy apelike or apeman creatures are not generally considered as possible groundsloth survivals, even though they are often reported on Islands of the West Indies where there were no significantly large monkeys BUT on some islands where some groundsloths were known to have persisted at least as recently as the European colonisation. In particular this means Puerto Rico, Hispanola and Cuba where the 'Yehos' or Devils are still reported, and the candidate groundsloths were smaller with rounder heads and still retaining some fanged teeth in the canine positions (some of these teeth are more incisorform and presumably were used in a more rodentlike adaptation) See especially Acratocnus on both drawinfgs. At the same time there are reports of a larger more bearlike creature from Cuba that could also represent one of the other local types of groundsloths (once again usually called Yehos or Yahus, meaning Devils, and said to be an African name originally)

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