Knowing that “Joe” is a Parasaurolophus less than a year old and a quarter of its final adult size, we can learn all sorts of things about how Parasaurolophus changed as it grew up. For instance, we know that Parasaurolophus grew incredibly fast during its first year of life–it would have had to eat a lot of plant food to keep that up!
The skull is perhaps the most informative part of “Joe”‘s skeleton, in terms of understanding how Parasaurolophus changed as it grew. Although adult Parasaurolophus had a tube-like crest, the crest on “Joe” was only a little bump. This shows that the shape of the crest morphed drastically through the life of a single animal.
Things get even more interesting when we compare Parasaurolophus to other duck-billed dinosaurs with crests. For instance, Corythosaurus had a much thinner and simpler crest than Parasaurolophus. We know from skulls of young Corythosaurus that they didn’t sprout their headgear until they were approximately half-grown–much later in life than Parasaurolophus.
Young Corythosaurus, even though their skulls are larger when they develop ornamentation, have crests that are superficially similar to the baby Parasaurolophus “Joe”. This provides an important clue for how Parasaurolophus evolved its extreme crest. Compared to its close relatives, Parasaurolophus modified the timing of its skull development. By sprouting its crest way earlier in life, and growing the crest for a much longer period of time, Parasaurolophus achieved very different skull anatomy from its close evolutionary cousins.