They also found a partially eaten specimen, the victim of a bird of prey, he added.
The gray-faced sengi is distinguished by its gray face and black lower rump as well as its size.
The insect-eating mammal is up to 8.3 inches (21 centimeters) longer, counting the tail, and 25 to 50 percent heavier than any other known elephant shrew, the study team says.
Elephant shrews were initially named because their long, flexible snouts give the animals a superficial resemblance to elephants. But recent genetic studies have shown, ironically, that elephant shrews are much more closely related to elephants than to true shrews.
Scientists now recommend using the African name "sengi" for elephant shrews to better separate them from "true" shrews.
The newfound species is the fourth member of the genus Rhynchocyon, a group known generally as giant elephant shrews because of their large sizes, Rovero said.
(See a giant elephant shrew video.)
"They are confined to East Africa and are mainly forest dwellers," the researcher added.
He described the group as "living fossils" that are little changed from species that lived 35 million years ago.
The gray-faced sengi's extra bulk may be an adaptation that helps the mammal retain heat, as it has been found living only in damp mountain forests at heights of least 3,280 feet (1,000 meters).
The find is reported in the latest issue of the Journal of Zoology.
Surveys suggest the new species is confined to just two populations in the Udzungwa Mountains.
It is set to be listed as endangered by the World Conservation Union, Rovero said, though the animal's isolation gives it a favorable outcome.
Giant elephant shrews are traditionally hunted by local tribes, the researcher noted.
"They are big enough prey for eating," he said. "But the new species is not too close to people, because it's in a forest reserve."
The mammal's range falls within the Udzungwa Mountains National Park and the newly announced Kilombero Nature Reserve, said Nike Doggart of the Tanzania Forest Conservation Group, a nongovernmental organization based in Dar es Salaam.
"During the recent surveys we recorded few signs of disturbance, including hunting and tree-cutting, in the areas where the elephant shrew has been recorded," Doggart said in an email.
"The remoteness of the species range contributes to its protection," she added. "However, human populations are growing in adjacent areas. This may pose a threat in [the] future as demand for land and forest resources in the Udzungwas increases."
The mountains form part of the Eastern Arc range, widely considered one of the planet's richest biodiversity hot spots.
The region harbors at least a hundred species of mammals, birds, amphibians, and other vertebrates found nowhere else, Doggart noted.
"Given that the moist forests of the Eastern Arc only cover about 3,300 square kilometers [1,275 square miles], this represents one of the highest concentrations of endemic species in the world," she said.
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