Old Frilly Face: Triceratops’ relative fills fossil-record gap

March 20, 2002 at 11:25 am

Fossils of a creature the size of a large house cat cast new light on the early evolution of the group of horned, herbivorous dinosaurs that later included the 8-meter-long Triceratops.

CERTAINLY NOT “NO FRILLS.” Artist’s conception of an adult and juvenile Liaoceratops, one of the earliest species of dinosaur with a frill across the back of its skull. 2002 Michael Skrepnick, Courtesy of The Field Museum

This group, the ceratopsians, was one of the last and most diverse sets of dinosaurs, says Peter J. Makovicky of The Field Museum in Chicago. One major ceratopsian subgroup included psittacosaurids, which were bipedal, parrot-beaked creatures that briefly flourished about 140 million years ago. The other subgroup consisted of the so-called neoceratopsians, which sported bony frills at the rear of their skulls. Neoceratopsians roamed Earth until dinosaurs went extinct about 65 million years ago.

Until now, the oldest neoceratopsian fossils were those of Archaeoceratops, a species that lived between 99 million and 112 million years ago. The newly discovered species–dubbed Liaoceratops yanzigouensis to honor the Chinese province and village where the animal’s remains were first discovered–roamed Asia at some time between 128 and 145 million years ago.

Liaoceratops‘ skull had a blunt, beaked face and a small but relatively thick frill. Pitting on the frill’s front edges indicates the creature’s jaw muscles were anchored there, says Makovicky. The thickness of this bony structure enabled it to withstand the forces required to chew tough vegetation.

The small horn on each cheek might have helped members of the species recognize their own. The structures probably didn’t have any defensive purpose because they were broad, blunt cones rather than spikes, says Makovicky. The 3-kilogram, 1-m-long dinosaur almost certainly depended on camouflage or speed to avoid predators.

In the March 21 Nature, Makovicky and his colleagues recount their analysis of two fossil skulls–one from a nearly adult animal and the other from a juvenile. Skeletal remains of other specimens, which are still being extracted from stone, should reveal the lengths of the animal’s front and rear limbs. The relative proportions of the limbs may suggest how Liaoceratops walked.

The new frilled fossils appear in a paleontological gap between the age of Archaeoceratops and the time when neoceratopsians split from the psittacosaurids. The finding suggests that the neoceratopsians’ frill may have evolved much more rapidly than scientists had previously thought, the researchers say.

Also, the two Liaoceratops skulls that Makovicky and his colleagues studied have some features that heretofore had only been seen in their psittacosaurid cousins.

“[Liaoceratops] shows that the evolution of ceratopsians is more complicated than we’d thought,” says Catherine A. Forster, a vertebrate paleontologist at the State University of New York at Stony Brook. “These fossils make things much more interesting.”