Record-breaking reptile.

Record-breaking reptile

The Lower Carboniferous period, lasting from 360 million to 320 million years ago, saw many important evolutionary changes in reptiles, amphibians and arthropods. Yet only a few tantalizing fossils remain to hint at what occurred.

Four years ago, paleontologists searching for fossils in a Scottish quarry found a cornucopia of carboniferous amphibians and arthropods, including the oldest known amphibian and the earliest daddy longlegs spider (SN: 4/13/85, p.237).

The same quarry, called East Kirkton Limestone, has now yielded a 338-million-year-old reptile -- almost 40 million years older than the previous record holder, reports Timothy R. Smithson of the Cambridge (England) Regional College. The almost complete fossil skeleton, 20 centimeters long, contains characteristic bones in the skull, spine and hind ankles that distinguish it from an amphibian, he says. Smithson, who also took part in the 1985 discovery, describes the specimen in the Dec. 7 NATURE.

"East Kirkton's been turning up some weird stuff," comments paleobiologist Nicholas Hotton III of the National Museum of Natural HNistory in Washington, D.C. The 1985 amphibians "really revolutionized which goes where with respect to reptilian ancestry." Before that find, Hotton says, a group of primitive amphibians with reptile-like feet and skulls represented the most likely candidates for reptile ancestors, but near their temples they had well-defined "otic nothces" -- which reptiles lack -- and their descendants retained that characteristic until they went extinct. Some of the East Kirkton amphibians, however, had no otic notches.

Having in hand the oldest known reptile may provide another clue to the mystery of how and when reptiles evolved, Hotton says.

From the pattern of its skull, Smithson has placed the ancient creature among the amniotes, an assemblage of reptiles, birds and mammals whose embroys feature an amniotic membrane. Further study of the specimen may help clarify the evolutionary relationship between amniotes and nonamniotes, he says.