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Fossil from Madagascar Rewrites Evolution of Mammals

Nov 05, 2014 04:42 PM EST

A fossil from Madagascar of a massive, groundhog-like creature is rewriting the evolutionary history of mammals, according to recent research.

Some 66 to 70 million years ago, an unusual veggie-eating mammal named Vintana ("Luck") sertichi lived along carnivorous dinosaurs of the Late Cretaceous. Weighing about 20 pounds, it was roughly twice the size of a modern day groundhog and enormous compared to most other mammals of its era.

Given its strange features, including a huge skull and eye sockets and turned-down snout, scientists say that they could never have predicted its existence. That is, until 2010 when a team of scientists from Stony Brook University stumbled upon a nearly complete cranium of the mammal in Madagascar.

"We know next to nothing about early mammalian evolution on the southern continents," project leader Dr. David Krause said in a statement. "This discovery, from a time and an area of the world that are very poorly sampled, underscores how very little we know. No paleontologist could have come close to predicting the odd mix of anatomical features that this cranium exhibits."

Rewriting History

The new fossil belongs to a group of early mammals known as gondwanatherians, primitive creatures living on the ancient supercontinent known as Gondwana that until now were known only from isolated teeth and jaw fragments.

"Gondwanatherians were completely unknown 30 years ago," Krause told National Geographic.

Not only is the discovery helping to reveal more about poorly understood habits and relationships of gondwanatherians, but the lucky find is also helping paleontologists fill in the mammalian evolutionary tree, especially during the age of the dinosaurs.

"The discovery of Vintana will likely stir up the pot," Krause added in the statement. "Including it in our analyses reshapes some major branches of the 'family tree' of early mammals, grouping gondwanatherians with other taxa that have been very difficult to place in the past." (Scroll to read on...)

(Photo : Reuters/Joseph Groenke/Stony Brook University) The cast of the skull of Vintana sertichi (foreground) with a lifelike reconstruction.

After a comprehensive analysis of the skull - measuring almost five inches long, twice the size of the previously largest known mammalian skull from the entire dinosaur age - Vintana shows that gondwanatherians are related to two other early groups of mammals known as multituberculates and haramiyidans. Together, they form a larger group called Allotheria, or "other beasts."

And given that haramiyidans are now classified as being in Allotheria, which date back to the Late Triassic, the origin of mammals has just been pushed back by about 25 million years.

"In essence, it really shakes up the early mammalian family tree and helps to reorganize it," Krause said via Reuters.

Krause explained to Discovery News that it's possible that "Luck" might have survived the mass extinction event that wiped out all the dinosaurs - with the exception of birds - some 65 million years ago, although fossil evidence has yet to be found. Perhaps like one shrew-like ancestor also from Madagascar, it slept through the dino extinction by hibernating underground.

Mystery Mammals

Regardless, the toothy beast is shedding some light on mammalian evolution after this point, although more has yet to be learned of Vintana himself.

So far, researchers can tell from various features of its fossil skull - despite missing the lower portion of the jaw - that Vintana was agile, with keen senses of hearing and smell. For example, it had powerful jaw muscles for chewing on plants, as evidenced by its large huge cheekbone attachments for jaw muscles, called flanges. In addition, it was a sniffing machine, with 14 percent of its brain mass taken up by its olfactory bulbs - the part of the brain involved in smell.

"It's very interesting and peculiar," added paleontologist Zhe-Xi Luo, who was involved in the study. "The very exotic combination of its skull features are so beyond our previous imagination."

However, much more remains to be seen of Vintana, and scientists plan to continue field explorations to learn more about this ancient creature and the early evolution of mammals.

The fossil and study findings are described in further detail in the journal Nature.

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