The removal of a 79 million-year-old dinosaur fossil from the mudstone of north-central Montana has brought to light something rarely seen.
“When everything was cleaned, it revealed this little crest – a tiny little stubby crest on its head – like nothing we’d ever seen,” said Elizabeth Freedman Fowler, an adjunct professor at Montana State University and curator of paleontology at the Great Plains Dinosaur Museum in Malta.
Turns out the dinosaur, a duck-billed dino that is believed to be an early ancestor of Montana’s state dinosaur – the Maiasaura – fills in a missing link in the evolution of the species.
“We knew what lived earlier and later,” Fowler said. “Now we’ve found a new species that is filling in that gap.”
“It’s a pretty important dinosaur considering the fact that it shows an evolutionary transition,” said Jack Horner, professor of paleontology at Montana State University. “You don’t see that too often. Most of the snapshots we get of animals are so separated in time that we only see different species.”
The fossil remains are described in a PLOS ONE article released on Wednesday that was co-authored by Fowler and Horner.
The fossil was named Probrachylophosaurus bergei, and nicknamed “Super Duck” because it was such a large member of the duck-billed dinosaurs. “Pro” means before in Latin. “Brachylophosaurus” is Greek for short-crested lizard.
Probrachylophosaurus bergei fits nicely between Acristavus gagslarsoni, which lived about 81 to 80 million years ago, and Brachylophosaurus canadensis, which lived about 77.8 million years ago. Acristavus had no crest upon its head, Probrachylophosaurus had a “small, flat triangular bony crest” and Brachylophosaurus had a big flat nasal crest.
“Most fossil animals are so far apart in time from their closest relatives that we can’t see that change,” Horner said.
Fowler noted that even some modern birds have big, flashy crests atop their heads made of either feathers, bone or keratin – the material that makes fingernails.
“The feature is normally for display to attract a mate,” Fowler said, showing every other bird that it has good genes, is sexually mature and healthy. As a bird grows, the size and shape of the crest may change.
Scientists speculate that dinosaurs used crests atop their heads for much the same reason.
“When we were trying to figure out their function, they’re not good for much,” Fowler said. “They couldn’t be used for fighting like elk antlers. That’s why we hypothesized they’re for display.”
Since the size of the crest appears to grow larger in duck-billed dinosaurs over time, and starts growing faster and earlier in later species, Fowler said evolution was obviously selecting for the trait as a valuable one. Unlike some species, though, it appears that both male and female duck bills had crests atop their head, although they could have been colored or patterned differently.
The Super Duck fossil – estimated to be 14 years old at time of death, weighing about 5 tons and measuring roughly 30-feet long – was larger than any other Brachylophosaurus fossil found.
“It’s really good that Super Duck was big because when we name a new species we want to make sure it’s an adult,” Fowler said.
That ensures that the fossil has reached maturity and won’t change much, if any.
Super Duck was originally found in 1981 along the high plains north of Rudyard, close to the Montana-Canada border along the Milk River drainage. The fossil was excavated in 2007 and 2008 by field crews from Bozeman’s Museum of the Rockies and then cleaned in the museum’s lab.
“It’s a wonderful area up there,” Fowler said. “This particular area exposes rocks that aren’t exposed in many other places.”
Fowler said that’s because glaciers scoured and gouged layers of soil and rock bringing the fossils closer to the surface.
“The country up there is flat, lots of wheat fields, but it drops down every now and then,” Fowler said. “There are dinosaurs under all of those wheat fields.”
Horner said the site near Canada exposes rock from the Judith River Formation that isn’t found in other places around Montana, giving fossil hunters a different snapshot of earth’s ancient history.
The University of California Museum of Paleontology conducted a dig at the site and removed some bones in 1981 and 1994, but never explored the site any further.
“The bones were scattered, so you have to be dedicated to keep digging,” Horner said.
He visited the site in 2007 after weather had exposed bones from the fossil’s head. Although Super Duck had been spread about the site and some bones crushed as it was buried in an organic-rich muddy floodplain, the skull case remained intact enough to reveal the dinosaur’s unusual crest.
“We were very lucky that was preserved,” Fowler said. “If we wouldn’t have had that, we couldn’t have named it.”
The front of the dinosaur’s nose was broken. And there were a lot of tyrannosaurus teeth found at the site, indicating that Super Duck may have either been killed or scavenged by the large predators. Also unusual, and the basis for a future paper, is that the nose of Super Duck appears to have healed from the bite of another creature, Fowler said.
“At the moment I’m leaning toward a large crocodile, because the puncture holes are round like a crocodile’s teeth,” she said.
Horner has been exploring for dinosaurs along the Hi-Line since the 1970s, and now his former students, including Fowler, are carrying on the work he initiated.
“I’m really proud of all my doctoral students,” he said. “When I started in that area in the 1970s, I only found fragmentary stuff.”