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UCR to help clear the air in national parks

UCR to help clear the air in national parks

(January 31, 2001)

Looks can be deceiving.

Elephants and aardvarks and golden moles, seemingly very different creatures, evolved from a single ancestor in Africa more than 65 million years ago, while dinosaurs still roamed the earth.

Writing in the Feb. 2 issue of Nature, biologists at the University of California, Riverside and colleagues from around the world have found the strongest genetic proof yet that relationships between major groups of mammals - including primates and humans - are more related to the ancient geography of supercontinents than to physical similarities.

In the past, scientists have hypothesized that mammals evolved and later entered Africa from the north after land connections were in place. Advances in DNA technology have shaken up that evolutionary tree.

'We analyzed almost 9000 base pairs of DNA for representatives of all major placental groups,' said Mark S. Springer, UCR associate professor and a lead author of the study, called 'Parallel Adaptive Radiations in Two Major Clades of Placental Mammals.'

'The most surprising result is a fundamental split between major groups that originated in the Northern Hemisphere versus groups that originated in the Southern Hemisphere.'

Springer said aquatic mammals, hoofed mammals and insectivores evolved on independent evolutionary tracks in different parts of the world.

'The golden mole and the elephant are closer relatives than the golden mole to the true mole,' Springer said.

Sometimes DNA evidence confirms traditional groupings. For instance, rabbits, guinea pigs and rodents probably do belong together, according to the Nature article. Sometimes the genetic evidence defies traditional theories. For instance bats are kin to hedgehogs, not flying lemurs.

The biologists have a very simple explanation for the divergence and resulting evolutionary tree. The animal relationships closely parallel the movement of continental land masses during geologic time.

'Laurasiatheria' is a category of animals springing from a common ancestor on the land mass that includes North America, Europe and Asia. That category includes carnivores, whales, even-toed ungulates (cows, pigs, hippos), odd-toed ungulates (horses, rhinos, tapirs), and insectivores such as moles, shrews, and hedgehogs.

Another group of animals, including primates and rodents, appears to have originated in the Northern Hemisphere also.

In the Southern Hemisphere, there are also two distinct groups. 'Afrotheria' includes elephants, aardvarks, sea cows, elephant shrews, hyraxes, golden moles, and tenrecs, all native to Africa. 'Xenarthra' includes anteaters, armadillos and sloths, native to South America.

'With the exception of 'Xenarthra,' these new groups are entirely unexpected based on anatomy,' Springer said. 'However, evolutionary trees based on DNA are exciting from the perspective of plate tectonics and the fossil record. Groups that originated in the Northern Hemisphere cluster together just as groups that originated in the Southern Hemisphere do.'

Springer said DNA trees even suggest that placental mammals, which bear young developed in the womb, may have their most recent common ancestry in the Southern Hemisphere. That finding disagrees with the conventional view. 'On classic evolutionary trees, the northern and the southern groups are all mixed up.'

Sorting out evolutionary relationships is important to establish the associations between animals - including humans - and to understand how animal life diversified on Earth, Springer said. A better understanding of evolutionary relationships will guide biomedical and veterinary scientists in choosing which animals to use in studies of disease and possible treatments. It will also guide decisions about the conservation of genetic diversity.

'Recent advances in DNA technology, such as the Human Genome Project, will make it possible to pinpoint the exact relationships between humans and other placental mammals over time,' said Springer.

Other authors on this paper are: Ronald W. DeBry, from the University of Cincinnati; Ole Madsen and Wilfried W. deJong of the University of Nijmegen, The Netherlands; Mark Scally, Christophe J. Douady, Diana J. Kao and Heather M. Amrine of UCR; Ronald Adkins of the University of Massachusetts; and Michael Stanhope of Queen's University of Belfast.

Funding for the study came from the National Science Foundation and the European Commission's Training and Mobility of Researchers program.

The University of California, Riverside ( is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 21,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion.

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