Scientists find oldest placental mammal fossil
ABC ONLINE 26/04/2002
A team of Chinese and American scientists say they have found a 125-million-year-old
fossil of an animal that is the most primitive known relative of today's higher mammals,
including humans and primates.
The remains of the creature, Eomaia scansoria, push back the fossil records of so-called
placental mammals by millions of years and provide a wealth of information about them.
Mammals that nourish their young in the womb through an organ called the placenta account
for the vast majority of all mammals, with a few notable exceptions such as marsupials.
"This mammal could be our great, great aunt or uncle, or it could be our
great-grandparent 125 million years removed," Dr Zhe-xi Luo of the Carnegie Museum of
Natural History in Pittsburgh said.
"Across a wide range of mammals we all share one common ancestry. We are all
placental mammals. With this new fossil we can trace the root of all the placental
group."
The tiny creature, which was no bigger than a large mouse, scurried on the ground at the
feet of the dinosaurs and may have made a tasty treat for some of its monstrous
contemporaries.
Its detailed features - teeth, foot bones and fur - suggest it lived in low branches and
bushes, was adapted for climbing and fed on insects.
"We have extended the quality record to the earliest time interval of placental
evolution," Dr Luo explained.
The fossil will allow scientists to determine which features placental mammals have
inherited from their earliest ancestors and which are newly evolved characteristics of the
group.
"In order to distinguish those two possibilities for any anatomical features, we have
to trace back to this earlier fossil record. That is why it is so exciting," Dr Luo
said.
Before the discovery of the fossil, which is reported in the science journal Nature, the
earliest record of a placental mammal was a few isolated 115-million-year-old teeth.
The new find was discovered in a quarry in the Liaoning Province of China, an area where
remains of feathered dinosaurs and very primitive birds have also been found.
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