A team of paleontologists said this week that some sauropod species went through drastic changes in skull shape during normal growth.

Researchers came to the conclusion after examining the The skull of a juvenile sauropod dinosaur, rediscovered in the collections of the Carnegie Museum of Natural History.

The fossil offers a rare chance to look at the early life history of Diplodocus, a 150 million-year-old sauropod from western North America.

The researchers believe these changes in skull shape may have been tied to feeding behavior, with adults and juveniles eating different foods to avoid competition. Young Diplodocus, with their narrower snouts, may also have been choosier browsers, selecting high quality plant parts.

Diplodocus carnegii adult and juvenile feeding

(Reconstruction illustration: Mark A Klingler / Carnegie Museum of Natural History)

"Adult sauropod skulls are rare, but juvenile skulls are even rarer," said John Whitlock, co-author of a paper in the Journal of Vertebrate Paleontology describing the research. "What we do know about the skulls of sauropods like Diplodocus has been based entirely on adults so far."

"Diplodocus had an unusual skull," said Jeffery Wilson, assistant curator at the University of Michigan Museum of Paleontology. "Adults had long, square snouts, unlike the rounded or pointed snouts of other sauropods. Up until now, we assumed juveniles did too."

The small Diplodocus skull, however, suggests that major changes occurred in the skull throughout the animal's life.

"Although this skull is plainly that of a juvenile Diplodocus, in many ways it is quite different from those of the adults," Whitlock said. "Like those of most young animals, the eyes are proportionally larger, and the face is smaller. What was unexpected was the shape of the snout—it appears to have been quite pointed, rather than square like the adults. This gives us a whole new perspective on what these animals may have looked like at different points in their lives."

Citation: Whitlock JA, Wilson JA, Lamanna MC, 'Description of a nearly complete juvenile skull of Diplodocus (Sauropoda: Diplodocoidea) from the Late Jurassic of North America', Journal of Vertebrate Paleontology, March 2010, 30: 442–457; doi:10.1080/02724631003617647