ancient-mouse-size-creature-uproots-mammal-family-tree

Ancient mouse-size creature uproots mammal family tree

By Charles Q. Choi
Published December 19, 2015
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An illustration of Haramiyavia, the earliest known proto-mammal, whose
identity is based on a reconstruction of its 210-million-year-old
fossil jaw (superimposed on bottom illustration). (April Neander)

An illustration of Haramiyavia, the earliest known proto-mammal, whose
identity is based on a reconstruction of its 210-million-year-old
fossil jaw (superimposed on bottom illustration). (April Neander)

Three-dimensional computer models of fossils from a tiny mouse-size
creature that lived about 210 million years ago in what is now
Greenland clear up a long-standing mammal mystery.

The high-tech analysis of the fossils suggests that [178]mammals
originated more than 30 million years more recently than previously
suggested, the researchers say.

Paleontologists analyzed fossils of haramiyids, extinct relatives of
modern mammals that lived about 210 million years ago. For decades,
researchers only had isolated teeth from haramiyids, stymying
investigations into where these creatures fit on the mammalian family
tree. [[179]See Images of 2 Tiny Early Mammals from China]

This uncertainty about where haramiyids belonged raised two
possibilities. One was that [180]haramiyids were crown mammals â€" the
branch of the mammal family tree that all modern mammals descend from â€"
suggesting that mammals began to diversify more than 210 million years
ago in the Triassic Period. The other was that haramiyids occupied a
separate branch at the base of the mammal family tree, suggesting
instead that mammalian diversification began about 175 million years
ago in the Jurassic Period.

To help solve this mystery, scientists analyzed a remarkably
well-preserved jaw from a haramiyid species known as Haramiyavia
clemmenseni, discovered in Greenland in 1995.

"These fossils are extremely rare," study lead author Zhe-Xi Luo, a
paleontologist at the University of Chicago, told Live Science. "You
have to go into the Arctic tundra and search for tiny little bits of
fossils."

The paleontologists theorized that Haramiyavia was a small creature,
weighing from 50 to 70 grams, or about twice as much as an adult mouse.

"As the earliest known haramiyid, Haramiyavia is the key piece of
evidence for inferences about the timeline of early mammalian
evolution," Luo said in a statement.

The researchers used high-resolution computed tomography (CT) scans to
develop 3D computer models of the jaw that helped them investigate this
specimen in unprecedented detail.

"With the CT scans, we were able to see every little piece of this
fossil," Luo said.

This high-tech analysis revealed many primitive structures in the
Source .... : http://www.foxnews.com/science/2015/12/19/ancient-mouse-size-creature-uproots-mammal-family-tree.html
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