Scientists have reported the discovery of what they say is the youngest, smallest and most complete fossil skeleton yet known for Parasaurolophus, a duck-billed plant-eating dinosaur that lived throughout western North America 75 million years ago.
Parasaurolophus is well-known for a long and hollow bony tube on the top of its skull, which paleontologists speculate was used like a trumpet to blast sound for communication, as well as a billboard for visual display. Although partial skulls and skeletons of full-grown Parasaurolophus have been known for almost a century, scientists previously knew little about how this species grew up.
The young Parasaurolophus, dubbed ‘Joe,’ was unearthed by student Kevin Terris in Grand Staircase-Escalante National Monument, southern Utah, in 2009. Joe was less than 6 feet long and under a year old when it died, and would have grown to an adult measuring 25 feet long.
Intriguingly, the fossil shows that Joe had a low bump on top of its head, which only later morphed into the curved tube of adults.
“Our baby Parasaurolophus is barely one-quarter of adult size, but it had already started growing its crest. This is surprising, because related dinosaurs didn’t sprout their ornamentation until they were at least half-grown. Parasaurolophus had to get an early start in order to form its unique headgear,” said Dr Andrew Farke from the Raymond M. Alf Museum of Paleontology, who is the first author of a paper published in the open-access journal PeerJ.
“Dinosaurs have yearly growth rings in their bone tissue, like trees. But we didn’t see even one ring. That means it grew to a quarter of adult size in less than a year,” added co-author Dr Sarah Werning of Stony Brook University.
The fossil skeleton has yielded previously unknown information about Parasaurolophus and its relatives. Medical scans documented the internal anatomy of the animal’s skull, allowing a reconstruction of its vocal capabilities.
“If adult Parasaurolophus had ‘woofers,’ the babies had ‘tweeters.’ The short and small crest of baby Joe shows that it may have had a much higher pitch to its call than did adults. Along with the visual differences, this might have helped animals living in the same area to figure out who was the big boss,” Dr Farke said.
Bibliographic information: Farke AA et al. 2013. Ontogeny in the tube-crested dinosaur Parasaurolophus (Hadrosauridae) and heterochrony in hadrosaurids. PeerJ 1: e182; doi: 10.7717/peerj.182