Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, May 17, 1990 TAG: 9005170110
SECTION: NATIONAL/INTERNATIONAL PAGE: A-6 EDITION: METRO
SOURCE: N.Y. Times News Service
DATELINE: LENGTH: Medium
The skull, which was discovered in 1897 in Baylor County, Texas, has spent most of the years since it was unearthed in a drawer at the American Museum of Natural History in New York City.
Its discoverers, who named the animal Tetraceratops insignis, believed that it was an ordinary pelycosaur, a type of reptile that flourished during the Permian period before the rise of dinosaurs.
But Michel Laurin and his faculty adviser at the University of Toronto, Dr. Robert R. Reisz, have concluded that tetraceratops was actually a missing link that closes what had been a perplexing gap in the fossil record leading from primitive reptiles to man.
In an article being published today in the British journal Nature, Laurin and Reisz report that previous examinations of the tetraceratops skull had failed to disclose its true nature because the fossil was mostly encased in rock that was difficult to remove.
They said their own painstaking study revealed that the skull actually belonged to an animal intermediate between the lumbering pelycosaurs and the later therapsids, active animals known to paleontologists as "mammal-like reptiles."
In fact, they said, tetraceratops is "the oldest known therapsid" and not, as was formerly believed, a pelycosaur.
Paleontologists agree that mammals belong to a lineage that stems from the pelycosaurs, but until the new report, there was a conspicuous gap in the line of descent.
Pelycosaurs played the same ruling role in the Permian period - from 280 million to 230 million years ago - that dinosaurs played in the later Triassic, Jurassic and Cretaceous periods.
A characteristic of many pelycosaurs was a high, sail-like ridge consisting of a frame of verticle bony spikes linked by a membrane of flesh.
Paleontologists do not agree about the purpose of pelycosaur sails, but many believe that the sails were used as radiators, to cool the animals' blood in hot weather, and to collect the warmth of the sun on cool days.
This explanation implies that pelycosaurs were cold-blooded.
From the pelycosaur line arose the therapsids, mammal-like reptiles that had faces and teeth resembling those of wolves. They were almost certainly warm-blooded and were probably covered with fur.
The therapsids themselves were eventually eclipsed by a later line of reptiles called archosaurs, a line that included the crocodiles and dinosaurs, but the small, furry descendants of the therapsids kept the protomammalian design alive until the demise of the dinosaurs opened new evolutionary niches for them that eventually led the way to man.
by CNB