April 9, 2010
Rare Juvenile Diplodocus Skull Tells of Changing Dino Diets
The reconstructed skull of a juvenile Diplodocus as seen from the side and the top. From the Journal of Vertebrate Paleontology paper.
From movies to museum displays, the dinosaurs we most often see are fully mature animals. There are a few good reasons for this. The first is that the skeletons of adult dinosaurs are among the most impressive specimens in the whole of the fossil record, but it is also true that the bones of juvenile dinosaurs are relatively rare. Scientists are still learning about how dinosaurs grew up, and a long-forgotten discovery has shown how one of the most famous dinosaurs changed as it matured.
During the early 20th century, paleontologist Earl Douglass collected numerous dinosaur remains from what is today Dinosaur National Monument in northern Utah. Among the bones retrieved from the 150-million-year-old work were several skulls of Diplodocus, including one from an adult, one from a subadult and one from a juvenile—but the juvenile skull was never formally described. Now paleontologists John Whitlock, Jeffrey Wilson and Matt Lamanna have undertaken that task, and what they have found is that juvenile Diplodocus substantially differed from adults.
The skulls of adult Diplodocus are very strange. The nasal openings are placed far back on the skull near the eyes, and the front of the snout is squared-off with a row of peg-like teeth sticking out at the front. In the juvenile skull, by contrast, the snout is more rounded, and the teeth extend much further back along the jaws. As the authors of the new study suggest, this may indicate that adult and juvenile Diplodocus ate different things. While the square snout of the adults would allow them to indiscriminately crop low-lying vegetation, the juveniles would have been better-adapted to selectively browse on softer leaves. This would have been important as juvenile Diplodocus would require a large amount of high-quality foods to grow, and so their mouth shape may have allowed them to more easily pluck up the more nutritious foods they needed. Once they grew to adult size, however, this need for high-quality plant food would be reduced, and so the skull became reshaped to reflect the different feeding habits of adults.
Whitlock, J., Wilson, J., & Lamanna, M. (2010). Description of a Nearly Complete Juvenile Skull of Diplodocus (Sauropoda: Diplodocoidea) from the Late Jurassic of North America Journal of Vertebrate Paleontology, 30 (2), 442-457 DOI: 10.1080/02724631003617647
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Woah, that’s really interesting! So I’m guessing they also had a period of losing their baby teeth as they aged?
Very interesting. I have had a similar idea regarding t. rex. Specimens show that as hey grew, their slender teeth were replaced by thicker teeth. Some cite this as evidence that t. rex was a scavenger. But i though that it was because the juveniles hunted small prey (thescelosaurus, pachycephalosaurus) and then when they grew up they matured to much larger prey (triceratops, edmontosaurus). just a thought. But it is interesting seeing it found in a dinosaur. Boy do we still have a lot to learn.
Although the interpretation of the varying skull size and shape due to diet among juvenile and adult diplocaci is
plausible, it needs to be strengthened by some coprolitic/gastrolithic evidence. Changes in anatomy and morphology may be proper to the species, with little connection to diet. The smaller head of the adult could simply be an adaptation that takes weight off of the wonderfully long neck of the adult and places it somewhere else.