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News 1 Nov 07
Meet Your New Cousins, the Flying Lemurs
Ker Than LiveScience
National Geographic News 1 Nov 07
Flying Lemurs Are Primates' Closest Kin
A new genetic study claims to have settled a long-standing debate about which living group of mammals is most closely related to primates, which include monkeys, apes, and lemurs.
Our nearest nonprimate relatives are not tree shrews as once thought, researchers say—but another group of tree-dwelling mammals known as colugos, also known as flying lemurs.
Colugos are squirrel-size creatures that live in the rain forests of Southeast Asia. Only two species are known to exist.
Like flying squirrels, colugos have a wide membrane of skin between their limbs that, when fully extended, forms a kind of sail—allowing the animals to glide from tree to tree. (See an Asian primate, the tarsier, in flight.)
Previous DNA-based studies had suggested that primates, tree shrews, and colugos are closely related, forming a single evolutionary grouping that can be traced back to a common ancestral species. (Related news: "Fossils of 'Most Primitive Primate' Found Near Yellowstone" [February 1, 2007].)
But experts have continued to debate when and in what order the three groups diverged from one another.
The new study finds that the ancestors of tree shrews split off first, and then the primate and colugo lineages diverged. That means that colugos are primates' closest evolutionary cousins.
"Our molecular trees indicate that [primates and colugos] split approximately 86 million years ago, more than 30 million years before modern primates or colugos appear in the fossil record," said study co-author William Murphy.
Murphy and Jan Janec(ka, both of Texas A&M University in College Station, led the team of U.S. and German researchers who will publish their findings in tomorrow's issue of the journal Science.
The researchers performed a comparative analysis of rare genetic changes in the different mammal groups.
Seven such changes were found in common between primates and colugos, compared to only one between primates and tree shrews.
Such a discrepancy is likely only if primates and colugos had a more recent common ancestor not shared with tree shrews, the researchers said.
The primate-colugo relationship was also supported by a separate computer analysis, which compared differences in DNA sequences from fragments of 19 different genes totaling 14,000 base pairs of DNA.
Knowing the historical branching order of the three groups will help researchers reconstruct the genetic makeup of the ancestors to today's monkeys, apes, and humans.
"Our data suggest that a draft genome sequence of the colugo will be critical for understanding the changes in the genomes that led to early primates and provide a backdrop to those changes that ultimately led to humankind," Murphy said.
Eric Sargis of Yale University in New Haven, Connecticut, was not involved in the research.
"To understand the earliest evolutionary history of primates, it's essential to know which mammalian group primates diverged from most recently," he said.
Sargis said the new study is important, but it may not completely settle the debate over which mammal group is most closely related to primates.
One previous study examined an equally large genetic data set, he noted, but reached different conclusions.
"[Both studies] are part of the Mammal Tree of Life project, which will include analysis of more taxa and more data," Sargis said.
"The results of this larger collaboration may yield a different result than the one being published this week."
From the earliest days of biological classification, primates have been grouped together based on a number of shared characteristics: grasping hands, five fingers with nails rather than claws, and forward-facing eyes.
But the first primates may have had few obvious features in common with the apes and monkeys of today.
"The ancestors of early primates, colugos, and tree shrews did not resemble their modern forms," co-author Murphy said.
"The [physical] changes that led to the appearance of modern primates and flying lemurs happened millions of years after the genetic changes that divided the two lineages in the Cretaceous period."
The living creature that has retained the greatest physical similarity to the ancient common ancestor of all tree shrews, colugos, and primates may be the pentail tree shrew of Southeast Asia, Murphy noted.
The new evolutionary study also shows that the pentail tree shrew is the sole survivor of an ancient lineage long separated from other tree shrew species.
"We suggest that a global priority be placed on the conservation of the pentail tree shrew and its habitat," Murphy said, "as extinction of this one species would result in the loss of a 63-million-year-old lineage."
Yahoo News 1 Nov 07
Meet Your New Cousins, the Flying Lemurs
Ker Than LiveScience
A group of creatures resembling large flying squirrels is the closest living relative of primates, the group that includes apes and humans, according to a new genetic study.
The finding, detailed in the Nov. 2 issue of the journal Science, contradicts a study published earlier this year by another team, which concluded that the squirrel-like colugos are more closely related to Scandentia, a group that includes tree shrews, than to primates.
Found in Southeast Asia, colugos are colloquially called "flying lemurs," although they are not lemurs and they don't truly fly. The animals are larger than flying squirrels but have a similar skin fold, called a patagium, which they use for gliding. Coasting from tree to tree at dusk, they look like furry kites.
Colugos belong to a classification of mammals known as Dermopterans. Together with primates and Scandentia, they make up the single taxonomic unit, or "clade," known as Euarchonta (meaning "true ancestors").
The exact evolutionary relationships among the three groups are a topic of debate among scientists. There are three possibilities:
-Colugos and primates shared a common ancestor that split from tree shrews
-Tree shrews and colugos are more closely related to each other than to primates
-Primates and tree shrews are sister groups, and colugos are the odd ones out
A study published in a January issue of the journal for the Proceedings of the National Academy of Sciences (PNAS) used morphological comparisons of the three groups to determine that tree shrews and colugos are more closely related to each other than either is to primates.
A different picture
The new study, based on genetic comparisons, paints a different picture. Jan Janecka of Texas A&M University and colleagues compared rare genetic changes, called indels, in the genomes of members of the three groups. Indels are regions of insertion or deletion in areas of the DNA that code for proteins.
The team found that colugos and primates have seven indels in common. Only one indel matched up between primates and tree shrews, and no indels were shared between tree shrews and colugos.
"In short, these molecular data strongly suggest that colugos are the sister group to primates," said study team member Webb Miller of Penn State University.
In a second experiment, the team fed genetic data from five mammalian groups, including Primates, Dermopterans, and Scandentia, into a computer model to calculate when they diverged. The results suggested Primates, Demopterans and Scandentia shared a common ancestor as far back as 87.9 million years ago, when dinosaurs still walked the Earth.
According to the model, the three groups separated relatively quickly soon after. At 86.2 million years ago, the ancestors of tree shrews split from that of primates and colugos, and primates and colugos went their separate ways about 79.6 million years ago.
Based on the new findings, the team urges an effort to create a draft of the colugos genome. "Colugos are going to be a much more important species to study now that we know their relationship to primates," Miller said.
For selfish reasons
Mary Silcox, an anthropologist at the University of Winnipeg in Canada who was a co-author on the PNAS study had an open mind about the new findings and the final word on the Top 10 Missing Links Ancient Furry Featherweight Mammal Discovered Behind the Controversy: How Evolution Works Original Story: Meet Your New Cousins, the Flying Lemurs
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