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 Scientists on Wednesday announced the discovery of fossils of the
dinosaur they named Probrachylophosaurus bergei that was about 30
feet (9 meters) long, weighed more than 5 tons and donned a small,
triangular bony crest atop its skull.
It was a member of a plant-eating group called duck-billed
dinosaurs, known for beaks resembling a duck's bill, common during
the latter part of the Cretaceous Period.
Many duck-billed dinosaurs boasted head crests of various shapes and
sizes. Probrachylophosaurus, one of the earliest with a prominent
crest, offers insight into the evolution of these features, the
researchers said.
Its skull bones are very similar to those of Acristavus, a
duck-billed dinosaur from about 81 million years ago thought to be
its ancestor, and Brachylophosaurus, which lived about 78 million
years ago and is thought to be its descendant.
"Acristavus does not have a crest. The top of its skull is flat.
Brachylophosaurus has a large, flat, paddle-shaped crest that
completely covers the back of the top of its skull," said Elizabeth
Freedman Fowler, curator of paleontology at the Great Plains
Dinosaur Museum in Malta, Montana.
"It is a perfect example of evolution within a single lineage of
dinosaurs over millions of years."
Paleontologist Jack Horner of Montana State University and the
Museum of the Rockies added, "Because the fossil record is very
spotty and we only get glimpses of evolutionary trends, it is always
exciting to find evidence of transitional species."
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Freedman Fowler said she gave Probrachylophosaurus (pronounced
pro-BRAH-KEE-loh-foh-saw-rus) the nickname "Superduck" because it
was pretty big for a duck-billed dinosaur, although not the largest.
Growth rings in its leg bones, akin to annual growth rings in trees,
showed it was 14 years old, still not fully grown.
"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," Freedman Fowler said.
The scientists unearthed most of its skull, its pelvis, hind legs,
vertebrae and ribs near the north-central Montana town of Rudyard.
They unearthed less-complete remains of a second
Probrachylophosaurus, more of an adolescent in age.
The research was published in the journal PLOS ONE.
(Reporting by Will Dunham; Editing by Sandra Maler)
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