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 Tytuł: Analiza DNA ssaków...
PostNapisane: 26 kwietnia 2007, o 14:40 
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Jurajski allozaur
Jurajski allozaur
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Dołączył(a): 2 lipca 2006, o 13:32
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Analiza DNA ssak??w potwierdze hipotezÄ?, i?? niekt??re z nich to ??ywe skamienia??o??ci:

Cytuj:
Because of a combination of interest and improved technology, new species have been described at a fairly high rate in recent years. But new mammals remain fairly hard to come by; perhaps one new mammalian species a year is typical, and many of these are simply variants of well-described species. That's why the discovery of the Laotian rock rat was exceptional. Although it was clearly a rodent, it was visually distinct from the rodent species we're familiar with. When video of the rat appeared, its strange gait and comfort with humans enhanced the otherworldly impression it made. What exactly was this creature?

Its discoverers named it a new species. But a later publication suggested that the creature's strangeness wasn't because it was new, but rather because it might be old: it was proposed that the Laotian rock rat (Laonastes aenigmamus) was the last surviving member of a once-large group of rodents that was known only by fossils. Although the group had vanished from the fossil record 11 million years ago, the morphological similarities were striking. The rock rat, it was proposed, is a living fossil.

DNA sequence analysis has now joined the argument and comes down strongly in favor of the living fossil contention. Not only is the rock rat like nothing we've ever seen before, it's not much like anything we've ever sequenced before.

The authors of the new report sequenced a small set of genes (six genes totaling 5.5 kilobases) in species from every major group of rodents. They also examined a number of repetitive sequence elements from the same groups. The data suggested that the rock rat split from the rest of rodents about 44 million years ago. For context, all existing primates derive from a speciation event about 50 million years ago.

Given this sequence data, it appears that Laonastes is the only living member of an entire family of mammals, the otherwise extinct Diatomyidae. When I first reported on the rock rat, I suggested that it might provide a unique opportunity to test our ability to accurately resolve evolutionary trees based on little more than the appearance of fossils. It is a pleasure to report that the paleontologists got it almost exactly right: the relationships they proposed, as well as the dates of separation, are strongly supported by the new molecular data. This suggests that we can view relationships proposed solely due to fossil evidence with a bit more confidence.

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 Tytuł: żywa skamieniałość: Badania DNA gryzonia
PostNapisane: 28 kwietnia 2007, o 07:55 
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Jurajski allozaur
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Dołączył(a): 2 lipca 2006, o 13:32
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Cytuj:
Living Fossil: DNA puts rodent in family that's not extinct after all
Susan Milius


The Laotian rock rat, which is very much alive, belongs to a rodent family that scientists had assumed had vanished 11 million years ago, says an international research team that examined DNA evidence. The family resemblance was also suggested from fossil evidence last year.

Obrazek
ALIVE AND SNIFFING. An image from the first photo session with a living Laotian rock rat, taken in 2006, comes from retired Florida State University professor David Redfield, who, with biologist Uthai Treesucon, set out on a personal quest to find the living animal.
FSU Research in Review Magazine

The Laotian rock rat (Laonastes aenigmamus), or kha-nyou, was new to science in 1996 when a wildlife-survey team bought some specimens in a food market in Laos. Since then, scientists have debated what sort of rodent it is, even proposing that it belongs to a new family of mammals.

Now, researchers in five countries have finished the biggest rock rat–DNA analysis yet. Their study dashes the idea of the new mammal family, says Doroth??e Huchon of Tel Aviv University. The team argues for an even more dramatic solution: The rock rat is a member of a supposedly extinct family, the Diatomyidae.

"People think the world is explored, and it's not," comments mammalogist Darrin Lunde of the American Museum of Natural History in New York City.

The Laotians who live near the creature's rocky outcrops know of the animals. But until 1996, mammalogists hadn't encountered the dark, squirrel-size creature, which has a long skull, rounded ears, and a furry tail.

In 2005, researchers at the Natural History Museum in London placed the rock rat in a new family of mammals (SN: 5/21/05, p. 324: http://www.sciencenews.org/articles/20050521/fob3.asp), the first to be described since the bumblebee bat family in 1974. The Laotian rock rat's family, they claimed, belongs within the Hystricognathi group, which includes guinea pigs, chinchillas, and porcupines.

Huchon says that when she read about the new family, she was unconvinced because the researchers had studied DNA from only one of its sources within cells. She appealed to the London team for tissue samples to expand the genetic analysis. So did other researchers, and an international network was born.

Altogether, the researchers looked at two mitochondrial genes, four stretches of nuclear DNA, and genetic elements that insert themselves randomly into the genome. Overall, the lines of genetic evidence agreed, Huchon says.

The new species doesn't fit easily within the Hystricognathi group. Instead, its closest living relatives are African rodents called gundies, the researchers report in a paper now online for an upcoming Proceedings of the National Academy of Sciences.

Fossil evidence had indicated that the gundies are close relatives to the Diatomyidae family. In 2006, a team of paleontologists based at the Carnegie Museum of Natural History in Pittsburgh had argued that the rock rat is a Diatomyidae, making that family a Lazarus taxon, one that reappeared after seeming to be extinct.

Lawrence Flynn, a paleontologist who described some of the Diatomyidae fossils, says that he's happy to welcome a living member to that family. Flynn, at Harvard University's Peabody Museum in Cambridge, Mass., says that the rock rat has such a strong family resemblance that had independently suggested a connection.

Huchon's new genetic study makes "a very nice molecular confirmation," comments Ronald DeBry of the University of Cincinnati, who uses DNA analysis to examine rodent evolution.

_________________
TRANCE - muzyka duszy
ELECTRO-HOUSE - muzyka ciała

..:: WIĘC ŻYJ W SWOIM RYTMIE ::..


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 Tytuł:
PostNapisane: 28 kwietnia 2007, o 10:35 
Pisa??e?? ju?? o tym: http://www.dinozaury.com/forum/viewtopic.php?t=1101


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