Triceratops may no longer have an identity crisis. As paleontologists lock horns on whether these dinosaurs were just baby versions of the largerTorosaurus, the latest clues suggest the two were indeed separate species.
A new study reveals immature and adult examples of both Triceratopsand Torosaurus. “I don't see any clear fossil evidence that one dinosaur turned into the other,” says Nicholas Longrich. He and fellow Yale paleontologist Daniel Field make their case online February 29 in PLoS ONE.
Comparisons between the dinos, which both lived about 65 million years ago in western North America, start with their skulls. Like many horned dinosaurs, Torosaurus sported a sizable frill of bone perforated with two big holes. Triceratops, in comparison, wore an unusually short and solid crown.
Searching for adult Triceratops, Longrich and Field grouped 35 skulls based on how fused together the bones were. Several Triceratops skulls had completely fused, a sign of maturity in modern animals. SomeTorosaurus skulls showed bones still joined by sutures, which are hints of youth.
But fused bones may not be a reliable way to gauge age, says paleontologist John Horner of Montana State University in Bozeman. “We recently collected 100 new Triceratops specimens they haven't seen,” he says. “We see a lot of variety in bone fusion.”
In 2010 Horner blamed Triceratops' unusual frill on youth. Patches of thinning bone on some skulls were steps toward full-fledged holes and aTorosaurus adulthood, he and Montana State colleague John Scannella argued.
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