For fifteen years, paleontologists from Montana State University have returned annually to the Hell Creek Formation in the northwestern portion of the state looking for additional Triceratops specimens. Slowly but steadily, the researchers amassed enough fossils to reveal an interesting reality -- the now famous "three-horned face" of the stout rhino-like dinosaur had not always been as we know it today.
In a new study -- published this week in the Proceedings of the National Academy of Sciences -- scientists at Montana State have demonstrated how the facial structure of Triceratops evolved over the course of a million or so years.
What study author John Scannella and his colleagues found was that "over one to two million years at the end of the Cretaceous Period, Triceratops went from having a small nasal horn and long beak to having a long nasal horn and shorter beak."
Scientists had previously realized that the facial structure of the well-armored Triceratops -- which grew up to thirty feet in length and weighed upwards of 16,000 pounds -- changed as the dino matured. But this new study, analyzing the skulls of some 50 Triceratops, reveals how the species' face evolved over many, many lifetimes.
Such a revelations wouldn't have been possible if not for the fact that so many Triceratops are preserved in the Hell Creek Formation -- an outcropping of Upper Cretaceous and some lower Paleocene rocks named for Hell Creek, near Jordan, Montana, but which includes exposures in Montana, North Dakota, South Dakota and Wyoming.
Only a half-million years before the dinosaurs disappeared, at the tail end of the Cretaceous Period, Triceratops roamed the Earth in great numbers.
"Most dinosaurs are only known from one or a handful of specimens," Scannella said. "Some dinosaurs are known from a large number of specimens, but they're often found all in one place -- on a single stratigraphic horizon."
"The great thing about Triceratops is that there are a lot of them, and they were found at different levels of the Hell Creek Formation," Scannella explained. "When you have a larger sample size, you can learn much more about variation, growth and evolution."