After the (meteor) Fall.

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Common Ancestor of Mammals Is Plucked From Obscurity
By JOHN NOBLE WILFORD, NYT: February 7, 2013

<<Humankind’s common ancestor with other mammals may have been a roughly rat-sized animal that weighed no more than a half a pound, had a long furry tail and lived on insects.

In a comprehensive six-year study of the mammalian family tree, scientists have identified and reconstructed what they say is the most likely common ancestor of the many species on the most abundant and diverse branch of that tree — the branch of creatures that nourish their young in utero through a placenta. The work appears to support the view that in the global extinctions some 66 million years ago, all non-avian dinosaurs had to die for mammals to flourish.

Scientists had been searching for just such a common genealogical link and have found it in a lowly occupant of the fossil record, Protungulatum donnae, that until now has been so obscure that it lacks a colloquial nickname. But as researchers reported Thursday in the journal Science, the animal had several anatomical characteristics for live births that anticipated all placental mammals and led to some 5,400 living species, from shrews to elephants, bats to whales, cats to dogs and, not least, humans.

A team of researchers described the discovery as an important insight into the pattern and timing of early mammal life and a demonstration of the capabilities of a new system for handling copious amounts of fossil and genetic data in the service of evolutionary biology. The formidable new technology is expected to be widely applied in years ahead to similar investigations of plants, insects, fish and fowl. Pulled out of obscurity and given some belated stature by an artist’s brush, the animal hardly looks the part of a progenitor of so many mammals (which does not include marsupials, like kangaroos and opossums, or monotremes, egg-laying mammals like the duck-billed platypus).

Maureen A. O’Leary of Stony Brook University on Long Island, a leader of the project and the principal author of the journal report, wrote that a combination of genetic and anatomical data established that the ancestor emerged within 200,000 to 400,000 years after the great dying at the end of the Cretaceous period. At the time, the meek were rapidly inheriting the earth from hulking predators like T. rex. Within another two million to three million years, Dr. O’Leary said, the first members of modern placental orders appeared in such profusion that researchers have started to refer to the explosive model of mammalian evolution. The common ancestor itself appeared more than 36 million years later than had been estimated based on genetic data alone. Although some small primitive mammals had lived in the shadow of the great Cretaceous reptiles, the scientists could not find evidence supporting an earlier hypothesis that up to 39 mammalian lineages survived to enter the post-extinction world. Only the stem lineage to Placentalia, they said, appeared to hang on through the catastrophe, generally associated with climate change after an asteroid crashed into Earth.

The research team drew on combined fossil evidence and genetic data encoded in DNA in evaluating the ancestor’s standing as an early placental mammal. Among characteristics associated with full-term live births, the Protungulatum species was found to have a two-horned uterus and a placenta in which the maternal blood came in close contact with the membranes surrounding the fetus, as in humans. The ancestor’s younger age, the scientists said, ruled out the breakup of the supercontinent of Gondwana around 120 million years ago as a direct factor in the diversification of mammals, as has sometimes been speculated. Evidence of the common ancestor was found in North America, but the animal may have existed on other continents as well.

The publicly accessible database responsible for the findings is called MorphoBank, with advanced software for handling the largest compilation yet of data and images on mammals living and extinct. “This has stretched our own expertise,” Dr. O’Leary, an anatomist, said in an interview. “The findings were not a total surprise,” she said. “But it’s an important discovery because it relies on lots of information from fossils and also molecular data. Other scientists, at least a thousand, some from other countries, are already signing up to use MorphoBank.”

Michael J. Novacek, a paleontologist and provost for science at the American Museum of Natural History in New York City, said the system could assess each mammal on the basis of more than 4,500 possible traits, which is 10 times larger than previous databases. “At one point, I didn’t think we would ever finish,” Dr. Novacek said.

John R. Wible, curator of mammals at the Carnegie Museum of Natural History in Pittsburgh, who is another of the 22 members of the project, said the “power of 4,500 characters” enabled the scientists to look “at all aspects of mammalian anatomy, from the skull and skeleton, to the teeth, to internal organs, to muscles and even fur patterns” to determine what the common ancestor possibly looked like.

Outside scientists said that this formidable new systematic data-crunching capability might reshape mammal research but that it would probably not immediately resolve the years of dispute between fossil and genetic partisans over when placental mammals arose. Paleontologists looking for answers in skeletons and anatomy have favored a date just before or a little after the Cretaceous extinction. Those who work with genetic data to tell time by “molecular clocks” have arrived at much earlier origins. The conflict was billed as “Fossils vs. Clocks” in the headline for a commentary article by Anne D. Yoder, an evolutionary biologist at Duke University, which accompanied Dr. O’Leary’s journal report. Dr. Yoder acknowledged that the new study offered “a fresh perspective on the pattern and timing of mammalian evolution drawn from a remarkable arsenal of morphological data from fossil and living mammals.” She also praised the research’s “level of sophistication and meticulous analysis.” Even so, Dr. Yoder complained that the researchers “devoted most of their analytical energy to scoring characteristics and estimating the shape of the tree rather than the length of its branches.” She said that “the disregard for the consequences of branch lengths,” as determined by the molecular clocks of genetics, “leaves us wanting more.”

John Gatesy, an evolutionary biologist at the University of California, Riverside, who was familiar with the study but was not an author of the report, said the reconstruction of the common ancestor was “very reasonable and very cool.” The researchers, he said, “have used their extraordinarily large analysis to predict what this earliest placental looked like, and it would be interesting to extend this approach to more branch points in the tree” including for early ancestors like aardvarks, elephants and manatees. But Dr. Gatesy said the post-Cretaceous date for the placentals “will surely be controversial, as this is much younger than estimates based on molecular clocks, and implies the compression of very long molecular branches at the base of the tree.”>>

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Scientists Say They've Nailed Down
Most Precise Date of Dinosaur Extinction Yet
by Julie Kent, Cleveland Leader, February 8, 2013

<<Scientists now say that they believe that they have determined the most precise date yet for the extinction of dinosaurs on Earth. Researchers from an international team of scientists have been investigating the demise of the dinosaur, and by using dating techniques on rock and ash samples, they've determined that dinosaurs died out about 66,038,000 years ago, give or take 11,000 years. The date of extinction appears to coincide with the impact of a comet or asteroid.

Debate has been on-going in the scientific community as to whether the impact was the sole cause of a sudden demise of the dinosaurs, or if they were already in decline at the time of the massive impact. Some even question whether the impact happened as much as 300,000 years after they were already gone.

Published in the journal Science, the study involved researchers from Glasgow University in Scotland, Vrije University Amsterdam in the Netherlands, and Berkeley Geochronology Center and University of California, Berkeley.

It was in 1980 that the extinction of dinosaurs was first linked to a comet or asteroid impact. It is believed that a 110-mile wide crater known as Chicxulub located in the Caribbean off the Yucatan coast of Mexico is the result of that devastating impact. The crater is thought to have been created by an object 6-miles across, which threw debris into the atmosphere. This debris is still found around the world.

Last year, the international team decided to use these clues to put a more precise date on the extinction of the dinosaurs through examining the layers of archaeological record where they lie close to the last fossils of dinosaurs. Researchers looked at samples from Montana, where excellent dinosaur fossils have been unearthed. They also examined tektites from Haiti and volcanic ash from the Hell Creek formation in Montana. These samples were then analyzed in labs in the U.S. using a technique called "argon-argon dating" to determine their precise ages. This particular techniques utilizes the fact that the naturally radioactive element potassium slowly decays into argon with regularity. The argon-argon method is one of the most precise ways of determining how long a particular sample has been decaying. Researchers in Glasgow then conducted their own independent argon-argon analysis on rock samples, which then confirmed the results from the U.S.>>

[saturno2]

Here researches speak of " a model of explosive evolution of mammals"
I think there was a period of " evolutionary aceleration"
A great proliferation of life and species.
I think this phenomenon was in the Cretaceous Period.
Hence the great reptiles and large fems.