There are currently around 50+ genera of sloths organized into five families (Bradipodidae, Mylodontidae, Megalonychidae, Megatheriidae, and Nothrotherridae), with the vast majority of the taxa being the extinct, fossil forms; there are two genera of living/extant sloths (Bradypus and Choloepus). This diversity often means that a number of the genera are not well understood or represented by many specimens.. As such, while my preferred studies are on the functional morphology of these great animals, it is sometimes necessary to address taxonomic questions in order to ensure that the specimens being studied for functional morphology actually belong to the genus in question.

This issue came front and center during my graduate studies, and specifically resulted in my dissertation "Reassessing the Taxonomy and Affinities of the Mylodontinae Sloths, Glossotherium and Paramylodon (Mammalia: Xenarthra: Tardigrada)," where I established the criteria that officially separate Glossotherium and Paramylodon as distinct, albeit closely related, genera. Much of the emphasis was on differences of the crania, but there were distinct features of the post-cranial elements as well.

That project has led to one currently underway regarding the post-cranial anatomy of Glossotherium and Mylodon. Both were endemic to South America during the late Pleistocene and they are closely related. Their skulls are quite different, but they were embroiled in a nearly century long controversy who's conclusion left Mylodon without any specific post-cranial descriptions to help differentiate individual elements from those of other contemporary mylodontids.

(A) Skull of Mylodon darwinii as featured in Reinhardt (1879). (B) Skull of Glossotherium robustum as featured by Owen (1842).

In my dissertation I was able to show a size variation between these two, but it was often a guessing game as most limb elements were not associated with any crania to make the identification 100%. I am currently working with a specimen of Mylodon from the Field Museum in Chicago that has a skull and associated post-crania to compare against known Glossotherium specimens to begin establishing distinct characters and morphology. This work will aid later field work and post-collection identifications, which will then enable the scientific community to more effectively study these unique sloth genera.