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Scientists discover striking new species of cloud-forest rodent in Peru

Findings shed new light on evolution of Neotropical arboreal rodents

A strikingly unusual animal was recently described from the cloud-forests of Peru. The large rodent is about the size of a squirrel and looks a bit like one, except its closest relatives are spiny rats.  The nocturnal, climbing rodent is beautiful yet strange looking, with long dense fur, a broad blocky head, and thickly furred tail. A blackish crest of fur on the crown, nape and shoulders add to its distinctive appearance.

Isothrix barbarabrownae, as the new species has been named, is described in a recent issue of Mastozoología Neotropical , the principal mammalogy journal of South America.

Related quote

"The new species casts new light on the evolution of the entire group."
The journal cover, with a beautiful drawing by Velizar Simeonovski

The authors of the study found the rodent in 1999 while conducting field research in Peru's Manu National Park and Biosphere Reserve in Southern Peru along the eastern slope of the Andes. Extending from lowland tropical forests in the Amazon Basin to open grasslands above the Andean tree line, Manu is home to more species of mammals and birds than any equivalently sized area in the world.  "Like other tropical mountain ranges, such as the Himalayas, Ruwenzoris, Virungas and Kinabalu, the Andes support a fantastic variety of habitats," said Bruce Patterson, MacArthur Curator of Mammals at The Field Museum and lead author on the study. "These in turn support some of the richest faunas on the planet."

Although the Field Museum is famous for rapid inventory techniques that answer many biodiversity questions, surveys like this one are thorough, careful and time-comsuming. This discovery was part of a three-year sampling scheme that involved as many as 14 people for 10 weeks of fieldwork annually.  More about that effort can be found on the Manu Project pages.  Eleven other mammal species new to science were discovered during the same work, including other rodents, bats and a marsupial. Amazingly, nearly 1 in 10 species that the team encountered was an undescribed species!

The new rodent was discovered at an elevation of 6,200 feet (1920 m), shown by the red star in the map below. Little is known about its lifestyle because subsequent efforts to locate and observe the animal were fruitless.  I. barbarabrownae belongs to a family of rodents known as "spiny rats" because most of the species in that family bristle with spines. Its discovery has necessitated a re-examination of this tropical American family, especially its closest relatives, the bush-tailed tree rats found in South America's lowlands. As a result of the recent discovery, the authors have used The Field Museum's Pritzker Lab for Molecular Systematics and Evolution to resolve the evolutionary relationships among all of these rodents.  "The new species is not only a handsome novelty," Patterson said. "Preliminary DNA analyses suggest that its nearest relatives, all restricted to the lowlands, may have arisen from Andean ancestors. The newly discovered species casts a striking new light on the evolution of an entire group of arboreal rodents."

Locations of other members of the brush-tailed tree rat genus Isothrix

Paul Velazco, the junior author of this paper, was a PhD student at the University of Illinois at Chicago and student-in-residence at The Field Museum at the time this study was conducted. He is now a post-doctoral fellow at the American Museum of Natural History in New York.  The new species is named after Scientific Associate Barbara E. Brown, who has worked at The Field Museum since 1970.


Broader work published in Fieldiana

The work of the international field research team that discovered I. barbarabrownae stretched over three seasons (1999-2001) and 3000 meters (10,000 feet) of elevation.  The work resulted in the discovery of 11 additional species new to science in a single river valley: 1 opossum, 7 bats, and 3 rodents. In November 2006, a synopsis of the entire project was published in Fieldiana: Zoology, a scientific publication of The Field Museum. The article is called "Mammals and Birds of the Manu Biosphere Reserve, Peru." It lists 222 species of mammals, 94 of which are bats, and 1,005 species of birds, twice the number of bird species breeding in the United States and Canada combined.  "Students from San Marcos University in Lima made up two-thirds of the team collecting mammals, birds, and their parasites," Patterson said. "Peruvian students have described most of the new species while pursuing graduate studies overseas. Manu trainees are now enrolled in universities in Illinois, Texas, Michigan, Mexico and the United Kingdom." The research was sponsored by the National Science Foundation, the Museo de Historia Natural at the Universidad Nacional Mayor de San Marcos in Lima, and The Field Museum.

The new rodent is described in this 2006 paper from the journal Mastozoología Neotropical

The new rodent's evolutionary affinities are detailed in the 2008 article in the journal Molecular Phylgenetics and Evolution.

Bruce's interview with the Canadian Broadcasting Company's Quirks & Quarks on 27 Jan 2007 can be heard here