Monday, March 06, 2006

Smallest Triceratops Skull Described

Photo by Mark Goodwin, UC Berkeley Museum of Paleontology
A cast of the foot-long skull from the youngest Triceratops fossil ever found is on display in the Library of University of California, Berkeley's Valley Life Sciences Building. The actual skull is described by Mark Goodwin in the March issue of the Journal of Vertebrate Paleontology
"The baby Triceratops confirmed our argument that the horns and frill of the skull likely had another function other than sexual display or competition with rivals, which people have often argued, and allows us to propose that they were just as important for species recognition and visual communication in these animals," Goodwin said.

The baby's skull, along with a few vertebrae, teeth and bony tendons, were discovered by amateur fossil hunter Harley Garbani in 1997 in Montana's Hell Creek Formation, the source of many Triceratops and T. rex fossils

Although Goodwin's conclusions about the lifelong growth of Triceratops will be published later this year, the baby skull offers its own insights. For one, the surface of the skull shows grooves were blood vessels used to be, evidently to nourish a fingernail-hard covering of keratin that was similar to the thicker layer that covered the adult skull. Such horny coverings are often brightly colored in the living descendents of dinosaurs - the birds - suggesting that adult Triceratops and their young may have been colorful, too.

In addition, the scalloped edges of the baby's frill became mere wavy edges in the adults, although the scallops foreshadowed the development of triangular scales along the edge of the adult frill, probably an attribute of sexual maturity, Goodwin said. The two brow horns started out straight and short in the baby - they're about an inch long - but ended up long and curved forward in the adult, while the nose horn became larger, like that of a rhinoceros, although it was made of bone in Triceratops.

The brain case of the baby also changed significantly, he said. Hidden beneath the boney frills of the skull, the hazelnut-sized brain of the baby fit snuggly within protective bones not yet fused, so as to allow further brain growth. In the adult, the brain, about the shape and size of a small sweet potato, was completely encased in fused bones. The relative position of the bones of the braincase as the animal matured recapitulates the cranial evolution of Triceratops from a more basal ancestor, such as Protoceratops.

Mark’s coauthors on the new paper are William A. Clemens, a UC Berkeley professor of integrative biology and Museum of Paleontology emeritus curator who opened up the Montana area for fossil exploration more than 30 years ago; field colleague Jack Horner of the Museum of the Rockies at Montana State University in Bozeman; and Kevin Padian, UC Berkeley professor of integrative biology and Museum of Paleontology curator.