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"Grave Rober" Mystery Solved After More Than 100 Years

20 November 2012

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MessageToEagle.com - For more than 100 years, scientists have struggled to solved a mystery of the so-called “grave robber,” Necrolestes patagonensis - fossil mammal from South America - and its underground and burrowing lifestyle.

“Necrolestes is one of those animals in the textbooks that would appear with a picture and a footnote, and the footnote would say ‘we don’t know what it is,’” says co-author John Wible, Carnegie Museum of Natural History mammalogist and member of the discovery team that also includes researchers from Australia and Argentina.

Now, an international team of researchers, including John Wible, can finally solve the much-debated paleontological problem, placing this strange 16-million-year-old creature, with its upturned snout and large limbs for digging, in the mammal evolutionary tree.

Since its discovery in Patagonia in 1891, Necrolestes has been an enigma.


The Miocene mammal Necrolestes patagonensis ventures out of its burrow 16 million years ago in Patagonia, present-day Argentina. Necrolestes is now recognized as a member of a group long thought to have become extinct shortly after the extinction of the large dinosaurs at the end of the Cretaceous period. Credit: Reconstruction by Jorge Gonzalez, copyright Guillermo W. Rougier for PNAS use as needed.


Situating Necrolestes among its relatives in the fossil record answers one long-held question, but creates others; it reminds us that there is a lot we don’t yet know about the global impacts of the massive extinction event 65 million years ago and it challenges assumptions that the well-documented effects that occurred in western North America were experienced globally.

This finding unexpectedly moves forward the endpoint for the fossil’s evolutionary lineage by 45 million years, showing that this family of mammals survived the extinction event that marked the end of the Age of Dinosaurs.

This is an example of the Lazarus effect, in which a group of organisms is found to have survived far longer than originally thought.

Despite being excellently preserved, the mysterious fossils moved from institution to institution and researcher to researcher, the classification of Necrolestes changing with each new move.

As recently as a few years ago, Necrolestes still could not be definitively classified in a mammal group. A CAT scan of the ear region in 2008 led to another research team’s hypothesis that Necrolestes was a marsupial.

This classification intrigued Wible’s co-author on the paper, Guillermo Rougier from the University of Louisville, Kentucky. As a specialist in South American mammals, Rougier was not convinced that the marsupial identification was accurate, and he embarked on his own attempt to make a classification.

“This project was a little daunting, because we had to contradict 100 years of interpretation,” admits Rougier. During the process of preparing the fossil for further study, Rougier uncovered characteristics of the skull anatomy that had previously gone unnoted. Based on these newly revealed features, the research team came to the groundbreaking realization that Necrolestes belonged to neither the marsupial nor placental lineages to which it had historically been linked.

Rather, Necrolestes actually belonged in a completely unexpected branch of the evolutionary tree which was thought to have died out 45 million years earlier than the time of Necrolestes.

Part of the riddle of Necrolestes has always been its seemingly mismatched anatomical features, which never seemed to fit any single classification.


Reconstruction of the mysterious mammal, Necrolestes patagonensis, of Early Miocene Patagonia, often thought to be a marsupial, as a mole-like animal. Credits: Stanton F. Fink


Based on its decidedly upturned snout, sturdy body structure, and short, wide leg bones, researchers had always agreed that it must be fossorial—a burrowing mammal, specialized for digging and tunneling, perhaps even more than any other known burrowing mammal—but this trait didn’t make classification any easier.

This trait, however, didn’t make classification any easier.

In 2011, a newly discovered extinct mammal named Cronopio contributed to unlocking the mystery of the burrowing enigma.

Discovered by co-author Guillermo Rougier from the University of Louisville, Kentucky, in South America, Cronopio belongs to the Meridiolestida, a little-known group of extinct mammals found in the Late Cretaceous and early Paleocene (100–60 million years ago) of South America.

Not only were Cronopio and Necrolestes found to have remarkable similarities, they are the only known mammals to have single-rooted molars—most mammals have double-rooted molars. This conclusively showed that Necrolestes was neither a marsupial nor a placental mammal, and was in fact the last remaining member of the Meridiolestida lineage, thought to have gone extinct 45 million years earlier.

“If we didn’t know those fossils,” says Wible of Cronopio, “we might have come to the same conclusion that everybody else had—that the relationships of Necrolestes were unknowable.”

The mass extinction that ended the Age of Dinosaurs wiped out thousands of species. Included in the devastation were the Meridiolestida, the mammal group to which Cronopio and Necrolestes belong, cutting short their evolutionary lineage—or so scientists thought.

Before the conclusive identification of Necrolestes, only one member of the Meridiolestida was known to have survived the extinction event, and that species died out soon after, early in the Tertiary Period (65–1.8 million years ago). Necrolestes is therefore the only remaining member of a supposedly extinct group.

“It’s the supreme Lazarus effect,” comments Wible. “How in the world did this animal survive so long without anyone knowing about it?”

In the Lazarus effect, a species previously thought to be extinct is rediscovered—sometimes living, sometimes elsewhere in the fossil record. The Lazarus effect is well represented by the ginkgo tree, thought to be extinct until it was rediscovered growing in China in the 17th century.

The researchers believe that Necrolestes’s supreme burrowing adaptations are exactly what enabled it to survive for 45 million years longer than its relatives.

The researchers believe that Necrolestes’s supreme burrowing adaptations are exactly what enabled it to survive for 45 million years longer than its relatives. “There’s no other mammal in the Tertiary of South America that even approaches its ability to dig, tunnel, and live in the ground,” explains Wible.

The scientific paper resolving the mystery of Necrolestes appears today in Proceedings of the National Academy of Sciences.

© MessageToEagle.com

See also:
Can Scientists Really Resurrect Dinosaurs, The Neanderthal Man And Other Extinct Species?

Fascinating Gigantic Creatures Today Totally Extinct 13,000 Years Ago Coexisted With Early Americans

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