Featured Research

from universities, journals, and other organizations

After 121 years, identification of 'grave robber' fossil solves a paleontological enigma

Date:
November 19, 2012
Source:
Carnegie Museum of Natural History
Summary:
Researchers have resolved the evolutionary relationships of Necrolestes patagonensis, a paleontological riddle for more than 100 years. Researchers have correctly placed the strange 16-million-year-old Necrolestes in the mammal evolutionary tree, unexpectedly moving forward the endpoint for the fossil's evolutionary lineage by 45 million years and showing that this family of mammals survived the extinction event that marked the end of the Age of Dinosaurs.

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

An international team of researchers, including Carnegie Museum of Natural History scientist John Wible, has resolved the evolutionary relationships of Necrolestes patagonensis, whose name translates into "grave robber," referring to its burrowing and underground lifestyle. This much-debated fossil mammal from South America has been a paleontological riddle for more than 100 years. Scientific perseverance, a recent fossil discovery, and comparative anatomical analysis helped researchers to correctly place the strange 16-million-year-old Necrolestes, with its upturned snout and large limbs for digging, in the mammal evolutionary tree. 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. 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.

The scientific paper resolving the mystery of Necrolestes recently appeared in Proceedings of the National Academy of Sciences.

A paleontological riddle

Since its discovery in Patagonia in 1891, Necrolestes has been an enigma. "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. Wible is known for his work on the origins and evolutionary relationships among the three modern mammal groups: placentals (live-bearing mammals such as humans), marsupials (pouched mammals such as opossums), and egg-laying mammals (such as platypuses). 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.

Confusing anatomy

Part of the riddle of Necrolestes has always been its seemingly mismatched anatomical features, which never seemed to fit any single classification. 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, digging mammal. Burrowing mammals have a wide humerus (upper arm bone) that is specialized for digging and tunneling. The humerus of Necrolestes is wider than any other fossorial mammal's, indicating that Necrolestes was particularly specialized for digging -- perhaps more so than any other known burrowing mammal -- but this trait didn't make classification any easier. The simple triangular teeth of Necrolestes served it well in feeding on subterranean invertebrates. However, until recently, its teeth have proved of little help in classifying Necrolestes, because they are so simplified and show no unambiguous similarities to those of other mammals. Enter Cronopio.

The mystery solved

In 2011, a newly discovered extinct mammal named Cronopio was the key that unlocked the mystery of the burrowing enigma. Discovered by co-author Rougier 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."

Evolutionary implications

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. "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. "It must have been on the edges, in an ecological niche that allowed it to survive." The researchers point out that other extinct digging species are known by many specimens, while Necrolestes is only known from a few fossils from a narrow geographic area. This means it was not abundant in its time, which fits with the model of a life form existing in a marginal environment. Rougier comments, "In a way, while not related, it's somewhat similar to how the platypus lives today. There aren't many of them, they are found only in Australia, and they live in a specific niche among modern mammals -- just as Necrolestes is an isolated lineage only found in South America, with very few individuals living among large numbers of marsupials."

Future research

Necrolestes's survival for 45 million years longer than expected challenges more than a century of scientific thought on the effects of the Late Cretaceous extinction event in South America, and shows how scientific thought is constantly changing based on new evidence. For example, because the paleontological landscape is much better understood in North America and Eurasia, extinction models on those continents were assumed to apply to all continents. Rougier points out, "We can't do that anymore. This story is more complex, a very distinct picture. We're just getting there with South America."

Carnegie Museum paleontologist Matt Lamanna, who has conducted expeditions to Patagonia since 1998, agrees that South America is a hotbed for new paleontological discoveries. "A lot of what we think we know about the Cretaceous-Tertiary extinction comes specifically from western North America," he confirms. "As the fossil record in other regions of the world continues to grow, our understanding of that extinction will undoubtedly continue to change."

The research team is looking forward to filling in the 45-million-year gap between Necrolestes and its nearest known relatives, applying that knowledge to other related species that crossed the Cretaceous-Tertiary extinction boundary -- a seemingly South American phenomenon.


Story Source:

The above story is based on materials provided by Carnegie Museum of Natural History. Note: Materials may be edited for content and length.


Journal Reference:

  1. Guillermo W. Rougier, John R. Wible, Robin M. D. Beck, and Sebastian Apesteguνa. The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America. PNAS, November 19, 2012 DOI: 10.1073/pnas.1212997109

Cite This Page:

Carnegie Museum of Natural History. "After 121 years, identification of 'grave robber' fossil solves a paleontological enigma." ScienceDaily. ScienceDaily, 19 November 2012. <www.sciencedaily.com/releases/2012/11/121119151318.htm>.
Carnegie Museum of Natural History. (2012, November 19). After 121 years, identification of 'grave robber' fossil solves a paleontological enigma. ScienceDaily. Retrieved April 18, 2014 from www.sciencedaily.com/releases/2012/11/121119151318.htm
Carnegie Museum of Natural History. "After 121 years, identification of 'grave robber' fossil solves a paleontological enigma." ScienceDaily. www.sciencedaily.com/releases/2012/11/121119151318.htm (accessed April 18, 2014).

Share This



More Fossils & Ruins News

Friday, April 18, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Couple Finds Love Letters From WWI In Attic

Couple Finds Love Letters From WWI In Attic

Newsy (Apr. 17, 2014) — A couple found love letters from World War I in their attic. They were able to deliver them to relatives of the writer of those letters. Video provided by Newsy
Powered by NewsLook.com
Erotic Art Offers Glimpse of China's 'lost' Sexual Philosophy

Erotic Art Offers Glimpse of China's 'lost' Sexual Philosophy

AFP (Apr. 16, 2014) — Explicit Chinese art works dating back centuries go on display in Hong Kong, revealing China's ancient relationship with sex. Video provided by AFP
Powered by NewsLook.com
French Historians Fight to Save Iconic La Samaritaine Buildings

French Historians Fight to Save Iconic La Samaritaine Buildings

AFP (Apr. 15, 2014) — Parisians and local historians are fighting to save one of the French capital's iconic buildings, the La Samaritaine department store. Duration: 01:42 Video provided by AFP
Powered by NewsLook.com
Bee Fossils Provide Insight Into Ice Age Environment

Bee Fossils Provide Insight Into Ice Age Environment

Newsy (Apr. 12, 2014) — Archeologists have found many fossils in the La Brea Tar Pits, including those of saber-tooth tigers and mammoths. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins