Dr. Michael Ryan, curator and head of
vertebrate paleontology at the Cleveland Museum of Natural History, is the lead
author on new research published in the Canadian Journal of Earth Sciences that
names two new tribes of horned dinosaurs (ceratopsians) based on
characteristics related to frill (or head shield) ornamentation
.
The two new tribes, Nasutoceratopsini and Centrosaurini,
lived concurrently in the Late Cretaceous Period (74-76 million years ago) in
the same region of what is now western North America. The major distinction
between the two tribes is the ornamentation of the famous head frills all
ceratopsians have.
Nasutoceropsins were dinosaurs that had large,
broad frills that lacked well-developed ornamentation, suggesting they chose to
blend into their environments rather than stand out with impressive head
displays. By contrast, centrosaurins were a natural grouping of dinosaurs that
had highly ornamental frills. Other differences between the two tribes included
the length of horns that extended from their brows (nasutoceratopsins tended to
have longer brow horns) and the structure of the lower jaw.
The distinctions open fascinating new
questions, including whether a differing jaw structure resulted in the two
tribes not competing for the same food resources, which would explain why they
could live together in the same environments as modern black and white rhinos
do. Sadly, other questions might be impossible to answer.
“Nasutoceratopsins took a different
evolutionary path from their centrosaurine cousins that typically have highly
ornamented skulls,” said Dr. Ryan. “We believe that the skull ornamentation was
important for attracting mates. If nasutoceratopsins lacked boney
ornamentation, it’s possible that they may have used distinctive coloration
patterns, social behaviors or vocalizations, like modern birds do in their
courtship behaviors. But we’ll never know for sure since those latter features
don’t fossilize.”
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