In 1891, the argentine paleontologist Carlos Ameghino discovered the fossils of an animal that would give paleontologists worldwide a century of headaches. Until now, that is. The fossils, which include pieces of the body and most of the skull, belonged to a certain mole-like animal named Necrolestes patagonensis. Necrolestes lived during the early Miocene (around 20 million years ago) in Patagonia, where modern-day Argentina is. Scientists think that Necrolestes fed on worms and small insects, burrowing through dirt much like today’s moles do. Its skull shows an upturned nose, and it had strong forelimbs and short, wide bones—all traits suited for a burrowing animal.

The problem with Necrolestes was its ancestry. Where and who N. patagonesis came from has baffled scientists until just recently. Many paleontologists thought it had to be a placental mammal, but they couldn’t prove it. Five years ago, a group of researchers claimed this baffling specimen was a marsupial, but not everyone was convinced. Most agreed it was a mammal, but more specific classification could not be determined. Not until now.

Dr John Wible from the Carnegie Museum of Natural History and Dr Guillermo Rougier of the University of Louisville, Kentucky, with others, recently co-authored a groundbreaking study that scientists believe once and for all settled the Necrolestes debate. Wible and Rougier found undeniable evidence that Necrolestes belonged to a believed to have died out 45 million years before N. patagonensis existed: the Meridiolestida. This group of mammals lived in South America between 100 and 60 million years ago, and scientists had believed all except one species in Meridiolestida had died out along with the dinosaurs in the mass extinction 65 million years ago. The one species in the group that did survive the extinction event died soon after, and that species was thought to be the end of the Meridiolestida lineage. But Wible and Rougier’s study proved otherwise. The study found that Necrolestes and Cronopio dentiacutus, a member of the Meridiolestida, have similarities, especially in the skull anatomy. These two species were the only mammals with single-rooted molars, meaning they most likely came form the same lineage and since Cronopio belongs to the Meridiolestida, so does Necrolestes.

So, the verdict is in. Necrolestes patagonensis is a member of the mammalian group Meridiolestida. Did you hear that? That was the collective sigh of 122 years of frustrated paleontologists, finally resting easy knowing that Necrolestes has found its place on the tree of life.

Read more about Necrolestes at www.sci-news.com.

Find the original study in the journal Proceedings of the National Academy of Sciences.

The Paleontological Research Institution, Ithaca, New York, is pleased to sponsor Paleontology content for This View of Life. Founded in 1932, PRI has outstanding programs in research, collections, and publications, and is a national leader in development of informal Earth science education resources for educators and the general public.

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Published On: January 23, 2013

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