Why Torosaurus is not a Triceratops

May 02, 2012 | Author: AAAS MemberCentral Program Director Peggy Mihelich

A life-sized bronze statue of Torosaurus latus, a frilled dinosaur, that lived during the late Cretaceous period (between 70 and 65 million years ago), stands atop a large stone base outside the Yale Peabody Museum of Natural History, in New Haven, Connecticut. The replica of the plant-eating dinosaur, known for its large round openings in the frill, looks out onto Whitney Avenue, while unassuming pedestrians pass underneath it.

The statue was erected seven years ago in honor of O.C. Marsh, the famous 19th century fossil hunter who is credited with naming the dinosaur. Torosaurus has quickly become the museum's mascot.

To the average person, Torosaurus might easily be mistaken for another familiar and common dinosaur from the late Cretaceous, Triceratops prorsus. Marsh, who also named Triceratops, described the two as separate species and they have been classified as so ever since. That is until 2010 when two well-known paleontologists, John Horner and John Scannella, at the Museum of the Rockies in Bozeman, Montana, published a paper where they argued that Torosaurus was an adult version of a Triceratops.

Toroasaurus, they concluded, didn't exist.

Their findings put the Peabody in a sticky situation. Should they change the name on the plaque outside? Should they relable all their Torosaurus fossils Triceratops? As curators struggled with what to do, Yale Ph.D. graduate student Daniel Field and postdoc Nicholas Longrich, weren't ready to kill off Torosaurus and crown Triceratops. They had doubts and decided to put Horner and Scannella's theory to the test and see for themselves if the two were one in the same.

"This was a side project," says Field, a AAAS member. Field, 23, is studying bird evolution.

Field shows us some of his favorite bird fossils, specimens at the Peabody

Because dinosaurs evolved into birds, Field finds himself "dabbling" in dinosaur research on occasion, and because the museum houses some of the very best Torosaurus and Triceratops fossils in the U.S., he and Longrich had the specimens on hand to conduct a study.

Field and Longrich came up with three testable "predictions" that must be true for Torosaurus to be Triceratops. They are: "1) the species in question should have similar geographic and stratigraphic distributions, 2) specimens assigned to Torosaurus should be more mature than those assigned to Triceratops, and 3) intermediates should exist that combine features of Triceratops and Torosaurus." Longrich and Field, 2012. PLoS ONE

The first one is true, according Field. Both animals lived at the same time and their fossils are found in the same locations, the western part of the U.S. But, two and three are not. Field and Longrich found many bones that showed immature Torosaurus and mature Triceratops. That one alone nulls Horner and Scannella's theory, explains Field.

"These guys are different species," he says.

While there is still debate within the paleontological community over their conclusions, Horner for one isn't convinced by Field and Longrich's work, it's good enough for the Peabody, who considers the matter settled. "It's nice to know we don't have to rename the statue," Field notes. With Torosaurus's legacy secured, Field hopes that paleontologists will embrace and use their study's protocols the next time another case like this comes along.

In the video above, Field introduces us to Yale's Torosaurus and takes us through the study that proves this dinosaur is its very own species.

Long live Torosaurus!

Related Links:

Museum's fossil library a research treasure trove | AAAS member Hans Sues: 'We live in a golden age of paleontology'