Before Tyrannosaurus and Triceratops, there was “Superduck.”
While excavating at Montana’s Judith River Formation, researchers from the Museum of the Rockies discovered a new species of duckbilled dinosaur: Probrachylophosaurus bergei.
Nicknamed “Superduck” for its impressive size, this dinosaur lived about 79 million years ago and grew to about 30 feet in length. But it’s most important feature may be the small crest at the top of its skull. Because of this trait, researchers suggest that P. bergei may be a transitional species between the non-crested Acristavus and the large-crested Brachylophosaurus. The new fossil was described Wednesday in the journal PLOS ONE.
Probrachylophosaurus and its cousins were hadrosaurs – a family of duckbilled, herbivorous dinosaurs known for their strange and highly variable crests. These crests would grow – subtly in some species, extravagantly in others – as the individual aged into adulthood. Some modern birds, like cassowaries and hornbills, possess similar features.
“We think that the crests of dinosaurs were visual signals so that they could recognize members of their own species, and also tell whether the animal was mature or not,” says lead author Elizabeth Freedman Fowler. “This supports other evidence of most dinosaurs being very social animals, similar to most modern birds.”
But how did these crests develop and grow over evolutionary time?
Dr. Freedman Fowler and colleagues found that juvenile Probrachylophosaurus had a slightly smaller crest than fully-grown individuals, suggesting that the crests grew as the animals matured into adulthood. The same trend can be seen in the later Brachylophosaurus, but the final adult crest size is much larger. Cranial growth is clearly present in both animals, but the latter Brachylophosaurus must have either developed earlier or at a faster rate to achieve a larger crest. A change in the timing or the rate of growth of different parts of an animal is called heterochrony.
“[heterochrony] is a major way that evolution occurs, because altering the genes for timing is much simpler than having to evolve something new from scratch,” Freedman Fowler says.
But to really understand dinosaur evolution, researchers need large sample sizes. That’s why western North America – Montana in particular – is such an important region for paleobiology. The exposed rock of the badlands, free from excessive vegetation and city development, host scores of fossil specimen. Here, paleontologists seek to fill evolutionary gaps, find juvenile and sub-adult individuals, and determine just how dinosaurs lived and died.
“Even though paleontologists have been collecting dinosaurs in Montana for over one hundred years, we are still making exciting new discoveries every single year,” Freedman Fowler says. “You can't find anything new if you don't go out and dig for it.”