Mysterious armoured mammals were gigantic armadillos: Study

London, Feb 23 (IANS) Huge, armoured mammals that went extinct in the Americas at the end of the last Ice Age likely originated less than 35 million years ago from ancestors within lineages leading directly to one of the modern armadillo families, researchers reveal.

The team found that the closest relatives of glyptodonts -- some species of which may have weighed two tonnes or more -- include not only the giant armadillo which can weigh up to 25 pounds but also the four-ounce pink fairy armadillo or pichiciego.

With the assistance of South American colleagues and Ross MacPhee, a curator in the American Museum of Natural History's Department of Mammalogy, researchers received ancient DNA sample from undetermined species of Doedicurus - a gigantic glyptodont that lived until about 10,000 years ago.

Using a novel approach to recover genetic information from ancient specimens, the team successfully assembled the complete mitochondrial genome of Doedicurus.

“Ancient DNA has the potential to solve a number of evolutionary questions. In this case, we used a technical trick that allowed us to selectively enrich our Doedicurus DNA extract so that we had enough endogenous genetic material to work with,” said MacPhee.

Two molecular phylogeneticists -- Frederic Delsuc from University of Montpellier (France) and Hendrik Poinar of McMaster University (Canada) - then developed a set of computer-reconstructed ancestral sequences to reconstruct the complete mitogenome of this glyptodont.

The researchers found that glyptodonts likely had a much later origin - from ancestors within lineages leading to the modern armadillo family Chlamyphoridae.

“Contrary to what is generally assumed about the distinctiveness of glyptodonts, our analyses indicate that they originated only some 35 million years ago, well within the armadillo radiation," Delsuc noted.

"Taxonomically, they should be regarded as no more than another subfamily of armadillos, which we can call Glyptodontinae,” he explained in a paper reported in the Cell Press journal Current Biology.

The authors also point out that they were unable to identify any morphological features that confirm the close relationship of relatively enormous glyptodonts and much smaller living armadillos.

This might be partly due to the limitations of fossil evidence.

However, with the new genomic evidence challenging existing concepts of glyptodont evolution, paleontologists will be eager to test the molecular evidence with additional physical traits.

The researchers note that glyptodonts were a very successful group for most of their history and that the cause of their disappearance remains a major scientific question.