Evolutionary Debate Sheds Light On The Age Of Mammals
August 28, 2012

Fossil Shows That Ernanodon Was A Closer Relative Of The Pangolin

April Flowers for redOrbit.com - Your Universe Online

65 million years ago, dinosaurs like Tyrannosaurus and Triceratops disappeared, leaving Earth open to the rise of mammals. These strange creatures are only distantly related to the mammals alive today.

One of those unusual mammals, Ernanodon antelios, was only known from a single, highly distorted specimen until recently. This specimen raised more questions than it answered about habits and evolutionary relationships. In the most recent issue of the Journal of Vertebrate Paleontology, a team of researchers describes a second specimen of Ernanodon that sheds new light on this curious beast from the dawn of the "Age of Mammals."

The Age of Mammals is what many call the Cenozoic Era, which started approximate 65 million years ago and continues to the present date.  During this time between 60 and 80% of all animal species disappeared.

The new specimen of Ernanodon comes from rocks in Mongolia that were deposited 57 million years ago during a period known as the Paleocene Epoch.

"Ernanodon is a unique find and represents one of the most complete skeletons ever collected from the Paleocene of the Naran Bulak locality," said Alexander Agadjanian of the Borissiak Paleontological Institute of the Russian Academy of Sciences.

The original, distorted skeleton was found by a team of Soviet paleontologists, in 1979, but remained unstudied for more than 30 years. The new specimen, which preserves most of the arms, legs and backbone, is more complete than the original. Making a detailed comparison among the bones of the Ernanodon and those of modern animals, the authors of the new study concluded that Ernanodon was highly specialized for digging. Whether this digging was for food, shelter or both is unknown.

"Only a handful of Asian Paleocene mammals are known by their postcranial skeleton, which makes Ernanodon a unique source of very important information about its habits, lifestyle, and affinities," said Peter Kondrashov of A.T. Still University of Health Sciences, lead author of the study.

Elements of the Ernanodon, such as its strong limbs, long claws and simplified teeth have led to debate over the evolutionary relationships of this early mammal. Some have argued that it was an ancient relative of modern armadillos and anteaters. Others assert it was more closely related to a group of African and Asian ant-eating mammals known as pangolins or "scaly anteaters."

Pangolins, also known as tenggilings, are tropical dwelling mammals with keratin scales covering their skin, the only mammal with this adaptation. Out of the eight species, seven are nocturnal, with the exception of the long-tailed pangolin. They use their well-developed sense of smell to find small insects at night, and spend their days curled into a ball sleeping. Pangolins range in size from 12 to 39 inches and are found throughout Africa and Asia.

The new study concludes that Ernanodon was a closer relative of pangolins than armadillos, but that it represents a very early side branch of the pangolin family tree.

"Few other fossil mammals presented as many controversies in the scientific world as Ernanodon did and we are glad the new skeleton helped us resolve them," Kondrashov added.