- The Washington Times - Thursday, April 25, 2002

ASSOCIATED PRESS
Scientists say they have found the earliest known ancestor of an evolutionary lineage that includes most of today's mammals, a mouselike creature that lived 125 million years ago.
The fossil, found in northeastern China, is so well-preserved it shows traces of fur, giving researchers some of their best evidence yet on how mammals evolved during the age of dinosaurs.
"For scientists studying early evolution, this is a dream come true," said Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh, who led the team that discovered the fossil.
It is an early ancestor of placental mammals, which nourish their young through a placenta during an extended pregnancy, Mr. Luo and colleagues report in today's issue of the journal Nature. Most of today's mammals use a placenta, but not marsupials such as kangaroos or egg-laying monotremes such as the platypus.
"It's the first branch of the entire placental mammal tree," Mr. Luo said. He and colleagues named the creature "Eomaia scansoria" Eomaia is Greek for "dawn mother" and scansoria is a Latin term reflecting the creature's apparent climbing ability.
The tooth and bone structure suggests eomaia ate insects and was well adapted to climbing trees and bushes, keeping it out from underfoot of the enormous dinosaurs that roamed the Earth during that period.
"It's a very small, agile mammal," Mr. Luo said, "part of a revolutionary era in evolution."
Eomaia's climbing ability may have given it an advantage over other mammals in its environment, although that's just speculation, said Anne Weil, a Duke University paleontologist.
Despite its place in the lineage leading to placental mammals, eomaia probably reproduced more like today's kangaroos, with some development outside the womb, Miss Weil added.
The eomaia fossil may help reconcile two camps of scientists who use different methods for dating the age of animal ancestors.
Molecular biologists study the details of DNA collected from living animals to measure how long they have been evolving, the so-called "molecular clock" method.
Paleontologists, in contrast, use fossils to track when new animals first appeared.
The previous fossil record for ancestors of placental mammals had extended back about 85 million years while the molecular clock suggested a longer evolutionary time scale dating back at least 104 million years closer to the 125 million-year age the eomaia fossil suggests.

LOAD COMMENTS ()

 

Click to Read More

Click to Hide