Scientists who discovered a primitive, shrew-like Mongolian mammal fossil from 65 million years ago say the animal's emergence on the scene was not unlike that of another particular state of affairs " this one, actually.
According to scientists writing in a recent edition of the journal Nature, the recognition of the mammal "Maelestes gobiensis," discovered in 1997, led to an exhaustive study of the fossil record that shows modern mammals actually arrived in a big burst.
I bet you wonder what we're getting at here.
The dinosaurs, however, were around, too, and this posed a problem for the mammals because the dinosaurs were, well, great, big and mean, and ate them. These dinosaurs filled up all the ecological niches all the way to the top, leaving the little mammals running around the edges of the Cretaceous period, snarling after what scraps they could, like that hapless squirrel in "Ice Age."
These mammals never got big, never grew big brains, never developed opposable thumbs. Modern mammals, according to the article, are defined as those that gestate for a long period of time and have a placenta present during their pregnancy, i.e. "placental mammals." (Other types are marsupials, like possums and kangaroos, which have a pouch, and monotremes, which lay eggs, like the duck-billed platypus " they really don't count unless you hit one on the Indian Nations Turnpike.)
"We wanted to test whether there were any Cretaceous placentals," said paleontologist John Wible in a telephone interview with Reuters, for a story on the topic. "If the molecular dates are correct, we should be finding things that look like modern placentals in this time period and we are not."
They found that no Cretaceous mammals are related to any living placental mammals, Reuters reported. "They are just extinct dead ends," Wible said.
What happened 65 million years ago? Well, a great, big rock hit the Earth and wiped out all the dinosaurs. When all the big critters dropped, it A) gave the little mammals something good to eat, and B) opened up the Earth for something else to take over.
"You've got all of these ecological niches that were occupied by the dinosaurs," Wible said. "They go extinct, and you've got wide open spaces. It's like the Oklahoma land rush."
These mammals must have felt bad about taking advantage of those dinosaurs. Sixty-five million years later, their descendants would set up textbook committees to teach that they never existed.