The exquisite preservation of a new, partial skull of Parasaurolophus cyrtocristatus, a species of duck-billed dinosaur that lived during the Cretaceous period, finally revealed the structure of its bizarre ornamental crest after decades of disagreement.
Parasaurolophus is a genus of herbivorous ornithopod dinosaurs that is most strikingly characterized by a tubular crest.
Three currently recognized species, Parasaurolophus walkeri, P. tubicen, and P. cyrtocristatus, lived in what is now North America, about 76.5-73 million years ago (Cretaceous period).
Unlike Parasaurolophus walkeri and P. tubicen, which have long slightly curving crests, P. cyrtocristatus is unique in having a shorter crest that curves sharply over the back end of the skull roof.
Parasaurolophus cyrtocristatus was previously known from a single, partial specimen collected in New Mexico in 1923 by legendary fossil hunter Charles H. Sternberg.
The new skull was discovered in 2017 in the Fossil Forest Member of the Fruitland Formation in northwestern New Mexico.
Skull of Parasaurolophus cyrtocristatus: (A) photograph of right lateral side; (B) illustration of right lateral side; (C) photograph of left lateral side; and (D) illustration of left lateral side. Abbreviations: Bso – Basioccipital; Bsp – Basisphenoid; Exo – Exoccipital; F – Frontal; La – Lacrimal; Lsp – Laterosphenoid; Na – Nasal; Osp – Orbitosphenoid; Pa – Parietal; Pmd – premaxilla dorsal process; Pml – premaxilla lateral process; Po – Postorbital; Pr – Prootic; Prf – Prefrontal; Ps – Presphenoid; Sq – Squamosal. Image credit: Gates et al., doi: 10.7717/peerj.10669.
“The preservation of this new skull is spectacular, finally revealing in detail the bones that make up the crest of this amazing dinosaur known by nearly every dinosaur-obsessed kid,” said co-author Dr. Joe Sertich, curator of dinosaurs at the Denver Museum of Nature & Science.
“This just reinforces the importance of protecting our public lands for scientific discoveries.”
“My jaw dropped when I first saw the fossil. I’ve been waiting for nearly 20 years to see a specimen of this quality,” said lead author Dr. Terry Gates, a paleontologist at North Carolina State University.
“This specimen is truly remarkable in its preservation,” said co-author Dr. David Evans, the Temerty chair in vertebrate paleontology and vice president of natural history at the Royal Ontario Museum.
“It has answered long-standing questions about how the crest is constructed and about the validity of this particular species. For me, this fossil is very exciting.”
A group of Parasaurolophus cyrtocristatus being confronted by a tyrannosaurid in the subtropical forests of New Mexico 75 million years ago. Image credit: Andrey Atuchin.
About 75 million years ago, when Parasaurolophus cyrtocristatus lived in the region, North America was divided into two landmasses by a broad seaway.
Laramidia, the ribbon of land to the west, extended from today’s Alaska to central Mexico, hosting multiple episodes of mountain building in early stages of the construction of today’s Rocky Mountains.
These mountain-building events helped preserve diverse ecosystems of dinosaurs along their eastern flanks, some of the best-preserved and most continuous anywhere on Earth.
Parasaurolophus cyrtocristatus shared lush, subtropical floodplains with other, crestless duck-billed dinosaurs, a diverse array of horned dinosaurs, and early tyrannosaurs alongside many emerging, modern groups of alligators, turtles and plants.
“The skull of Parasaurolophus cyrtocristatus is still incompletely known, so more complete material will likely reveal new features that further differentiate this species and aid in determining the pace of ornamental crest evolution,” the paleontologists said.
The findings were published in the journal PeerJ.
T.A. Gates et al. 2021. Description and rediagnosis of the crested hadrosaurid (Ornithopoda) dinosaur Parasaurolophus cyrtocristatus on the basis of new cranial remains. PeerJ 9: e10669; doi: 10.7717/peerj.10669