Nothrotheriidae


Nothrotheriidae is a family of extinct ground sloths that lived from approximately 11.6 mya—11,000 years ago, existing for approximately. Previously placed within the tribe Nothrotheriini or subfamily Nothrotheriinae within Megatheriidae, they are now usually placed in their own family, Nothrotheriidae. Nothrotheriids appeared in the Tortonian, some 11.6 million years ago, in South America. The group includes the comparatively slightly built Nothrotheriops, which reached a length of about. While nothrotheriids were small compared to some of their megatheriid relatives, their claws provided an effective defense against predators, like those of larger anteaters today.

Evolution

During the late Miocene and Pliocene, the sloth genus Thalassocnus of the west coast of South America became adapted to a shallow-water marine lifestyle. However, the family placement of Thalassocnus has been disputed; while long considered a nothrotheriid, one recent analysis moves it to Megatheriidae, while another retains it in a basal position within Nothrotheriidae.
The earliest nothrotheriid in North America was Nothrotheriops, which appeared at the beginning of the Pleistocene, about 2.6 Ma ago. Nothrotherium reached Mexico by the late Pleistocene.
The last ground sloths in North America belonging to Nothrotheriops died so recently that their dried subfossil dung has remained undisturbed in some caves, as if it were just recently deposited. One of the skeletons, found in a lava tube at Aden Crater, adjacent to Kilbourne Hole, New Mexico, still had skin and hair preserved, and is now at the Yale Peabody Museum. The largest samples of Nothrotheriops dung can be found in the collections of the National Museum of Natural History.

Classification

Family †Nothrotheriidae

  • ?Subfamily Thalassocninae
  • * Genus Thalassocnus
  • Subfamily Nothrotheriinae
  • * Genus Amphibradys
  • * Genus Chasicobradys
  • * Genus Huilabradys
  • * Genus Mionothropus
  • * Genus Nothropus
  • * Genus Nothrotheriops
  • * Genus Nothrotherium
  • * Genus Pronothrotherium
  • * Genus Xyophorus

Phylogeny

The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data.