Olaf R.P. Bininda-Emonds, from the Friedrich-Schiller-University (Jena, Germany), and Andy Purvis, from the Imperial College (London, England), led a team of U.S. Canadian, and Australian researchers to produce the first nearly complete study of species-level mammals.

In all, the researchers studied DNA (deoxyribonucleic acid) and fossils of 4,510 of 4,554 known mammal species. Their surprising results are featured in the March 29, 2007 issue of the journal Nature.

Some of the startling results that came from their study include the contention that mammals did not begin to dominate on the Earth when mass extinctions of dinosaurs and other life forms occurred about 65 million years ago, during the end of the Cretaceous Period. Instead, Bininda-Emonds and Purvis contend that even though mammals were already well on their way before the mass extinctions, and that they were able to survive those devastations better than the dinosaurs, their dominance actually began ten to fifteen million years later.

They believe that the first mammals appeared around 220 million years ago and the first mammals that directly were related to today’s mammals appeared about 125 million years ago.

The Cretaceous Period occurred after the end of the Jurassic Period (about 145.5 million years ago) and before the beginning of the Paleocene Epoch of the Tertiary Period (about 65.6 million years ago). The Cretaceous-Tertiary (K/T) extinction event is believed to have occurred when a huge meteorite impacted in the Yucatan and the Gulf of Mexico, what is now called the Chicxulub impact crater.

The researchers also contend that diversification rates hardly changed as a result of the Chicxulub impact crater, but did change dramatically about 10 million years later and lasted for about 20 million years, what is now called the long-fuse model, a theory that places most intraordinal (relationships within orders) diversifications after the K/T boundary.

Therefore, these researchers contend that many of today’s mammalian orders actually originated about 100 to 85 million years ago, well before the end of the Cretaceous Period and its associated mass extinctions. The mammals that benefited most from the mass extinctions of 65 million years ago actually did not survive and are extinct today. The mammals that survived the mass extinctions of dinosaurs but only barely are the ones that are still around today. Such mammals include those that give birth to live young (placental mammals) such as carnivores (flesh-eating animals), ungulate (hoofed) mammals, primates (such as humans, apes, and monkeys), and rodents (characterized as gnawing mammals).

With mammals now dominating much later from what was earlier thought, scientists are now looking into the reasons why it took mammals so long to diversify.

{moscomment}

---

Get stories like this delivered daily - FREE - subscribe now
When you subscribe get a 12 months license for LiveProject
Valued at $99 USD


Download the FREE iTWire desktop alert widget