A new skull of a lost species reveals a bizarre, ancient animal

In 1676, the first dinosaur bone was dug up. At the time, the massive femur was thought to have belonged to a massive man, not a Megalosaurus. Over 300 years have passed since then and we're still learning new dinosaur facts — gathering details that create a looking glass into the past.

New research published in the journal PeerJ adds to our understanding of dinosaur history by focusing on another unique feature: a bizarre, tube-shaped crest resting on the skull of the rare Parasaurolophus cyrtocristatus. The study highlights the first such discovery of a Parasaurolophus cyrtocristatus skull in 97 years.

Brief background — The Parasaurolophus clade is part of a class of duck-billed dinosaurs known as hadrosaurids, which include the nasal-crested Lambeosaurinae family. According to fan legend, the Lambeosaurus was seen in concept art for Jurassic Park but was removed in the final cut of the movie.

The three known species in the Parasaurolophus family include Parasaurolophus cyrtocristatus, Parasaurolophus tubicen, and Parasaurolophus walkeri.

What's new — Scientists compared one newly discovered skull specimen from the Fruitland Formation, a geological site in New Mexico, to another fossil of Parasaurolophus cyrtocristatus in Utah.

Through this comparison, scientists were able to better map the evolution of the Parasaurolophus species and figure out just how it developed such a bizarre tube-shaped head crest.

Digging into the details — The new skull specimen allowed the researchers to confirm the dramatically arched head crest was linked to an incredibly unique nasal passage.

"Imagine your nose growing up your face, three feet behind your head, then turning around to attach above your eyes. Parasaurolophus breathed through eight feet of pipe before oxygen ever reached its head," Terry Gates, a paleontologist from North Carolina State University, said.

This crest was no mere flamboyant appendage. It served a crucial evolutionary purpose, according to researchers. They believe they may have finally figured out the meaning behind the crest after a century of scientific debate.

"Over the past 100 years, ideas for the purpose of the exaggerated tube crest have ranged from snorkels to super sniffers," David Evans, the Temerty Chair in Vertebrate Palaeontology and Vice President of Natural History at the Royal Ontario Museum, said.

Evans added, "But after decades of study, we now think these crests functioned primarily as sound resonators and visual displays used to communicate within their own species."

The study also challenges our understanding of the evolution of this crested dinosaur. Contradicting previous studies, the researchers found that the crest of the Parasaurolophus cyrtocristatus shares much in common with another type of hard-billed dinosaur known as a Lambeosaurus.

Beyond the crest, the researchers discovered that Parasaurolophus cyrtocristatus shares a close sister relationship with another dinosaur in the same family known as P. tubicen, explaining why fossils of both species were uncovered in northeastern New Mexico.

While previous studies mostly focused on the dinosaur's unique crest, this study revealed six new traits regarding the dinosaur's physique, such as the surprising lack of a muscle scar on the jaw and a vertically projecting squamosal — a skull bone found in amphibians, reptiles, and birds.

The researchers also wondered why, of all the bones in a dinosaur's body, was the crested skull so well preserved among existing Parasaurolophus cyrtocristatus specimens?

They hypothesized that the development of the crest led the dino's skull to become well-reinforced, ultimately preserving the specimen. So, we may be able to thank the dinosaur's crest for helping scientists find the Parasaurolophus cyrtocristatus millions of years after dinosaurs became extinct.

On the other hand, the crest may have been a heavy burden — literally.

"The greatly enlarged crests would certainly have put relatively more stress on the joints of the skull roof and braincase in Parasaurolophusrelative to other hadrosaurid taxa."

Why it matters — Scientists have known about P. cyrtocristatus for many decades, but poorly preserved specimens have prevented further study of the Parasaurolophus species.

This new study paints a more complete picture of P. cyrtocristatus, helping us understand the evolution of this rare species.

The study states:

These two new, remarkably preserved specimens permit a detailed understanding of external crest anatomy in a species of Parasaurolophus for the first time...

What's next — As with any study, this scientific finding paves a stepping stone for future research to expand on.

We still don't have enough archaeological material to draw further conclusions about the strange creature that was P. cyrtocristatus. Further research is required to fully understand the evolutionary function of the head crest.

The study states: "The skull of P. 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."

Abstract: For nearly 60 years, skulls of Parasaurolophus species have been differentiated primarily on the basis of crest shape rather than on unique morphologic characters of other cranial elements. Complicating matters is the fact that crests dramatically change shape throughout ontogeny. Without a complete growth series, it has become difficult to assess the taxonomic distinctness of each species through the lens of allometric growth. Parasaurolophus cyrtocristatus has proven to be especially troublesome to assess because of the poorly preserved nature of the type and only skull. A new, partial skull from the Fossil Forest Member of the Fruitland Formation—the same geologic unit as the type specimen—is the first opportunity to re-diagnose this species as well as redefine the genus with many new traits. An undescribed, short-crested subadult skull from the Kaiparowits Formation of Utah previously assigned to cf. P. cyrtocristatus allows detailed comparisons to be made between the unnamed Utah taxon and the material of this species from the type locality. We find that several characteristics of the squamosal, supraoccipital, and premaxilla shared between the referred skull and the type skull are unique to P. cyrtocristatus (senso stricto) within the genus, irrespective of the overall crest shape. A phylogenetic analysis that includes six new characters posits that P. cyrtocristatus and P. tubicen are sister taxa, and that the latter does not share a closest common ancestor with the long-crested P. walkeri as previously hypothesized. This result helps to explain why both taxa are found in northeastern New Mexico, USA and in sequential geologic units (Fruitland Formation and Kirtland Formation, respectively). Additionally, the exquisitely preserved new skull provides the first opportunity to unequivocally identify the osteological make-up of the Parasaurolophus cranial crest. Unlike in previous reconstructions, the crest composition in Parasaurolophus follows what is seen in other lambeosaurines such as Corythosaurus, where the dorsal process of the premaxilla dominates the crest, with the nasal forming 80% of the ventral paired tubes, and the lateral premaxillary process acting a lateral cover between the dorsal and ventral tubes. The skull of P. 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.