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Amanda Maxwell

Nov 29th 2021

How a Fossil Skull Solved a Mystery in Dinosaur Evolution

Fossils turn up all the time all over the world and rarely make the news. However, the 2017 discovery of an extremely well-preserved piece of skull in New Mexico is making headlines, as it helped scientists solve a long-standing mystery in dinosaur evolution. The report, published recently in PeerJ, describes how the Parasaurolophus skull fragment not only shows the anatomy of the dinosaur’s distinctive cranial crest but also helps to define the species at last.

Ancient Sandbar Reveals Treasure

According to Sci News, Parasaurolophus cyrtocristatus is a duck-billed dinosaur species that lived around 76.5 to 73 million years ago during the Cretaceous period. It is one of three species in the hadrosaurid family of dinosaurs that lived in the lush subtropical floodplains of the landmass that would form North America. Specimens have been gathered from sites as far apart as New Mexico, Utah and even Alberta, Canada. They are each characterized by a distinctive cranial crest that looks like the animal’s nostrils went wild and grew up the front of its face to curl back just behind the eye sockets. These hadrosaurids were herbivores and used batteries of grinding teeth that were continually replaced to chew through the rough vegetation.

During the 2017 survey in the Fossil Forest Member of the Fruitland Formation of northwest New Mexico, team members noticed the specimen partially exposed from natural erosion. Careful excavation revealed a well-preserved partial skull with a distinctive curved crest, along with a lower jawbone and some ribs.

Back at the lab, the research team found that the partial skull they were holding showed intricate features in the anatomy of the strange, curved structure. The fossil was the first to show a detailed anatomy of the crest outer surface. From examination, not only were they were able to define its anatomy, but they could also comment on how development of the crest affected skull morphology. The tubular structure grew from the nasal and premaxilla bones to form a hollow tube with an internal network of airways. As the distinctive crest enlarged with age, the skull itself had to mature faster to support the crest.

Dinosaur Evolution Revealed

Since the finding of the first skull in 1922, the three members of the Parasaurolophus family had been classified according to the shape of the crest. However, researchers weren’t sure if the fossil record represented three different species or if the specimens just showed different stages of development or perhaps sexual dimorphism, according to the PeerJ report. Paleontologists have also been uncertain about why the crest existed and what it was used for. The recent study helps to clarify these two issues in dinosaur evolution.

The most recent fossil is in a remarkable state of preservation thanks to its location in the ancient sandbar. This made it easier for the researchers to compare it with a similar, possibly juvenile specimen dug up in Utah to establish the species’ characteristics based on distinctive bony landmarks on the skull. Their analysis in the PeerJ report shows that P. cyrtocristatus is a distinct species and not just a step in dinosaur evolution for close relatives P. tubicen and P. walkeri. The skull fossil explains why specimens from the family were found in such diverse locations and during similar time periods.

Not a Snorkel

Finding well-preserved fossils can help to answer a lot of questions regarding dinosaur behavior. For example, fossil teeth can show not only what dinosaurs ate but also how they chewed. Intact specimens, such as those found in amber with preserved soft tissue structures, can also give clues to how ancient species hunted their food. The Parasaurolophus skull has helped to dispel the idea that these dinosaurs snorkeled.

Various theories were proposed to explain the distinctive crest. CNN lists one suggestion that the tube equipped the dinosaur as a super sniffer with increased olfactory abilities. Another theory suggested that Parasaurolophus dinosaurs grazed underwater, keeping the cranial crest above the water surface as a snorkel, so they could breathe while feeding. The anatomical detail in the latest fossil finds show that neither idea is possible.

Instead, the anatomical evidence suggests that the cranial crest was used mainly for display as it probably shows sexual dimorphism. The tubes may also have helped with thermoregulation — and perhaps communication. The internal network of airways may have acted as sound resonators. The duck-billed Parasaurolophus dinosaurs may have used their crests to amplify sound rather like a trumpet.

While researchers continue to speculate and theorize, the partial skull findings have certainly brought them closer to a clear image of what these ancient duck-billed dinos were like.

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