Sunday, October 22, 2006

BUBALUS CEBUENSIS: Philippines Extinct Dwarf Carabao



Almost 50 years ago, Michael Armas, a mining engineer from the central Philippines, discovered some fossils in a tunnel he was excavating while exploring for phosphate. Forty years later, Dr. Hamilcar Intengan, a friend of his who now lives in Chicago, recognized the importance of the bones and donated them to The Field Museum.

If not for the attention and foresight of these two individuals, science might never have documented what has turned out to be an extremely unusual species of dwarf water buffalo, now extinct.

The new species, described in the October issue of the Journal of Mammalogy, has been named Bubalus cebuensis (BOO-buh-luhs seh-boo-EN-sis) after the Philippine island of Cebu, where it was found. Its most distinctive feature is its small size. While large domestic water buffalo stand six feet at the shoulder and can weigh up to 2,000 pounds, B. cebuensis would have stood only two-and-one-half feet and weighed about 350 pounds.

B. cebuensis, which evolved from a large-sized continental ancestor to dwarf size in the oceanic Philippines, is the first well-supported example of "island dwarfing" among cattle and their relatives.

"Natural selection can produce dramatic body-size changes. On islands where there is limited food and a small population, large mammals often evolve to much smaller size," said Darin Croft, lead author of the study and a professor of anatomy at Case Western Reserve University.

Significant finding on several levels

Water buffalo are members of the cattle family and are placed in the genus Bubalus, which includes four living species. Two species, Bubalus bubalis and B. mindorensis are closely related, and the new fossil species appears to be a close relative of this pair.

B. bubalis is the well-known domestic water buffalo. B. mindorensis, popularly known as a tamaraw, is also a dwarf, although at about three feet tall at the shoulder and 500 pounds it is considerably larger than the newly discovered species. The highly endangered tamaraw lives only on the Philippine island of Mindoro. Two poorly known species of the genus Bubalus from the Indonesian island of Sulawesi, known as anoas, are more distantly related.

The new species, B. cebuensis, teaches scientists a great deal about the entire buffalo genus. Its discovery on Cebu--in combination with the occurrence of the rare tamaraw on Mindoro and a report of fossil teeth potentially referable to Bubalus on Luzon--indicates that this genus might have once lived throughout the Philippines, most of which is an oceanic archipelago, never connected to any continental land mass.

"Documenting past mammal diversity in the Philippines, an area of extremely high conservation priority, is vital for understanding the evolutionary development of the modern Philippine flora and fauna and how to preserve it," said Larry Heaney, a co-author of the study and curator of mammals at The Field Museum. "The concentration of unique mammal species there is among the very highest in the world, but so is the number of threatened species."

B. cebuensis also can help scientists to better understand "island dwarfing," whereby some large mammals confined to an island shrink in response to evolutionary factors. This may occur due to a lack of predators (the animal no longer needs to be large to avoid being eaten) and/or limited food (smaller animals require less food).

The research could provide insights into debates on the evolution of small-bodied species elsewhere in the tropics such as the proposed new hominid, Homo floresiensis, found on the Indonesian island of Flores in 2003. "Whether or not Homo floresiensis ultimately is shown to be a new dwarf hominid species, discovery of this new fossil water buffalo provides additional evidence that dwarf species can evolve quickly in isolation," said John Flynn, a co-author of the study, and chairman and Frick Curator in the Division of Paleontology at the American Museum of Natural History. "Other fossil dwarf mammal species likely remain to be discovered in the poorly explored island systems of tropical Southeast Asia."

The discovery of B. cebuensis supports the hypothesis that the tamaraw evolved to a small size due to its island habitat. Further, the fact that B. cebuensis lived on a smaller island than the tamaraw and evolved into a smaller size than the tamaraw supports the hypothesis that the size of an island plays a role in island dwarfing: the smaller the island, the smaller the dwarf.

The new discovery also shows that dwarfing can affect different parts of the body differently. For example, B. cebuensis had relatively large teeth, which is typical of island dwarfs, but also relatively large feet, which are usually reduced in dwarfing.

Scientists were able to determine the size and features of the new species based on a partial skeleton consisting of two teeth, two vertebrae, two upper arm bones, a foot bone, and two hoof bones. The fossil could not be dated with certainty, but the authors estimate that it probably lived during the Pleistocene ("Ice Age"), probably between 10,000 and 100,000 years ago, but it is possible that it is younger.

The discovery demonstrates that there are fossils to be found in the Philippines, which rarely produces fossils due to its hot, wet conditions, which are not conducive to fossil preservation. Only a few fossils of elephants, rhinos, pig, and deer have been found previously, according to Dr. Angel Bautista, a co-author of the study and curator of anthropology at the National Museum of the Philippines in Manila. "Finding this new species is a great event in the Philippines," he said. "We have wonderful living biodiversity, but we have known very little about our extinct species from long ago. Finding this new fossil species will spur us to new efforts to document the prehistory of our island nation."

The Philippines include more than 7,000 islands. During the last glacial maximum about 20,000 years ago, much of the water in the oceans was frozen in glaciers, resulting in much lower sea levels--about 400 feet lower. Because of this, some groups of current islands within the Philippines became connected by land. Some of the mammals, including water buffalo, probably migrated to the Philippines during these periods by swimming short distances between islands. Once the glaciers melted and sea levels rose, these mammals became isolated on their respective islands. Over the years, they evolved into the unique species found there today.

According to Heaney, about 200 native mammal species currently live in the Philippines, and nearly two-thirds of them are endemic (only found there). Only Madagascar has a higher percentage of endemic mammals.

"This discovery highlights the importance of making fossils available for scientific study," Croft said. "If not for the generosity of Mr. Armas and Dr. Intengan, we probably never would have known about this extinct species."

Source : Field Museum

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