Evolving Triceratops Evidence Found In Montana's Hell Creek Formation
July 2, 2014

Evolving Triceratops Evidence Found In Montana’s Hell Creek Formation

April Flowers for redOrbit.com - Your Universe Online

For the last 15 summers, research teams from the Museum of the Rockies have been exploring the badlands of Eastern Montana to excavate dinosaur bones from the Hell Creek Formation. Those teams have made many exciting and important discoveries regarding some of the last dinosaurs to walk our planet.

Their latest study, published in the Proceedings of the National Academy of Sciences, involves the evolution of perhaps one of the most popular dinosaurs, the Triceratops. Montana State University (MSU) doctoral candidate John Scannella and his colleagues examined more than 50 specimens collected in recent years to discover the new insights revealed in the study.

The team recorded precise stratigraphic (rock layer) data for each Triceratops, then analyzed the morphological details of the skull. This allowed them to see evolutionary trends in the Triceratops fossils.

They found that during a one- to two-million-year period near the end of the Cretaceous, Triceratops changed. The early Triceratops (Triceratops horridus) had a small nasal horn and a long beak and was only found lower in the Hell Creek Formation. By the end of the transformation, the Triceratops had a large nasal horn and a shorter beak. This Triceratops (Triceratops prorsus) was only found at the upper end of the Hell Creek Formation. The team found skulls near the middle of the Formation, however, that showed characteristics of both T. horridus and T. prorsus.

“This study provides a detailed look at shifts in the morphology of a single dinosaur genus over time,” Scannella said.

In 1999, MSU's Museum of the Rockies spearheaded an extensive survey of the Hell Creek Formation called the Hell Creek Project, which ran through 2010. Several other institutions joined in with the Project, with the goal of learning everything possible about the geology, flora and fauna of the formation in order to accurately reconstruct the environment present at the end of the Cretaceous Period. They wanted to understand the lives and evolution of the animals that inhabited that region, as well.

The Hell Creek Formation is a "paleontologist's dream," according to the University of California's Museum of Paleontology at Berkeley. The Formation is mainly exposed on state and federal lands, such as the Charles M. Russell National Wildlife Refuge, and consists of freshwater clays, mudstones and sandstones deposited during the last part of the Cretaceous, the Maastrichtian period.

Project members found that Triceratops was the most common dinosaur in the Hell Creek Formation, resulting in The Museum of the Rockies housing one of the most extensive Triceratops collections in the world.

“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.

“So we can compare Triceratops found at different levels,” Scannella said. “When you have a larger sample size, you can learn much more about variation, growth and evolution.”

Scannella's colleagues included MSU graduate student Denver Fowler, Mark Goodwin from the University of California Museum of Paleontology, Berkeley, and MSU Regents Professor of Paleontology, Jack Horner.

Previous to this study, Horner and Goodwin discovered that the skull and horns of Triceratops changed shape as the animal grew from infant to adult. Scanella and Horners suggested in 2009 that the animal's skull underwent even more dramatic changes than previously suspected. They believe that when fully mature, the Triceratops became what researchers previously thought to be a distinct genus of horned dinosaur, the Torosaurus.

“The new study finds evidence that not only did Triceratops change shape over the lifetime of an individual, but that the genus transformed over the course of the end of the age of dinosaurs,” Scannella said.

So many Triceratops bones were located during the Hell Creek Project that they are still being removed from field jackets and prepped for study on a daily basis at the Museum of the Rockies. The new fossils range from small juvenile specimens to adults with car-sized heads. Some of the fossils were found complete and intact, while others were shattered into countless pieces.

To put together the most comprehensive picture possible of the evolution of the Triceratops, the team members collected as many fossils as possible.

“The study emphasized how important it is to know exactly where dinosaur fossils are collected from,” Scannella said. “A beautiful Triceratops without detailed stratigraphic data cannot answer as many questions as a fragmentary specimen with stratigraphic data.”

The first Triceratops, found in 1887, wasn't recognized as a dinosaur at first. According to CNN, researchers mistakenly identified it as a buffalo. The dinosaur received its name, which means "three horned face" in Greek, from Yale scientist O.C. Marsh in 1889.

Image 2 (below): This Triceratops prorsus fossil came from the top of the Hell Creek Formation. The fossil is displayed at MSU's Museum of the Rockies. Credit: MSU Museum of the Rockies


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