Parasaurolophus

Parasaurolophus (/ˌpærəsɔːˈrɒləfəs, -ˌsɔːrəˈloʊfəs/; meaning "beside crested lizard" in reference to Saurolophus) is a genus of hadrosaurid "duck-billed" dinosaur that lived in what is now western North America and possibly Asia during the Late Cretaceous period, about 76.5–73 million years ago. It was a large herbivore that could reach over 9 metres (30 ft) long and weigh over 5 metric tons (5.5 short tons), and were able to move as a biped and a quadruped. This dinosaur is famous for its large, elaborate head crest, which was likely used for communication and making sounds.

Three species are commonly recognized: P. walkeri (the type species), P. tubicen, and the short-crested P. cyrtocristatus. Scientists first described Parasaurolophus in 1922 from a skull and partial skeleton found in Alberta. Remains have also been found in New Mexico, Utah, and possibly Heilongjiang.

Parasaurolophus belonged to a group of dinosaurs known for their unusual head decorations. Its long, curved crest may have helped it recognize others of its kind, make loud calls, or even control its body temperature. Though not as common as some other duck-billed dinosaurs, Parasaurolophus remains an important discovery for scientists studying life from the time of the dinosaurs.

Discovery and naming

The name Parasaurolophus means "near crested lizard" and comes from Greek words. It was first discovered in 1920 in Alberta by a team from the University of Toronto. The scientist William Parks named it P. walkeri to honor Sir Byron Edmund Walker. Another species, P. tubicen, was found in New Mexico and named for its trumpet-like crest. A third species, P. cyrtocristatus, was discovered in New Mexico and Utah and has a shorter, rounded crest.

Parasaurolophus has three recognized species: P. walkeri, P. tubicen, and P. cyrtocristatus. Each species looks different. P. walkeri has a simpler crest, P. tubicen has the largest and most complex crest, and P. cyrtocristatus has the smallest and most curved crest. These differences help scientists tell them apart.

Description

Parasaurolophus was a large dinosaur that lived about 76.5–73 million years ago. It could grow up to about 9.5 metres (31 feet) long and weigh more than 5 metric tons. This dinosaur had a special crest on the back of its head, which was hollow and had tubes inside.

Parasaurolophus could walk on two legs or four, depending on what it was doing. It likely used four legs when searching for food and switched to two when running. The dinosaur had strong bones and skin covered in small, tubercle-like scales.

Classification

Parasaurolophus was first thought to be closely related to Saurolophus because of its similar crest. But it was later found to belong to the lambeosaurine subfamily of hadrosaurids, which is different from the hadrosaurine subfamily that includes Saurolophus. It is usually seen as a separate group within the lambeosaurines, not the same as the helmet-crested dinosaurs like Corythosaurus, Hypacrosaurus, and Lambeosaurus. Its closest known relative might be Charonosaurus, another lambeosaurine from the Amur region of China. The two might form a group called Parasaurolophini. P. cyrtocristatus, which has a short, rounded crest, might be the most basic of the three known Parasaurolophus species, or it could represent younger or female examples of P. tubicen.

Paleobiology

Diet and feeding

As a hadrosaurid, Parasaurolophus was a large, two-legged and four-legged plant-eater. It had a special skull that let it grind food like we chew it. Its teeth grew constantly and were arranged in groups called dental batteries, with only some teeth used at any time. It used its beak to bite plants and held them in its mouth with a cheek-like organ. It could eat plants up to about 4 metres off the ground.

Growth

Parasaurolophus is known from many adult fossils and one young fossil, nicknamed Joe, found in 2009. Joe was about one year old when it died and measured just over 2.5 metres long. This fossil shows that the crest on its head started growing earlier than in related dinosaurs. Even though we don’t have a complete skull from between Joe’s age and adult age, we know the crest grew quickly as they got older.

Cranial crest

Scientists have many ideas about what the crest on Parasaurolophus’s head was for. It might have been used to show off to others of its kind, to make sounds to communicate, or to control its body temperature. We believe it could have done several of these things. The crest changed as the dinosaur grew and might have helped show if it was male or female.

Temperature regulation hypothesis

The large surface area of the crest might have helped Parasaurolophus control its temperature. Scientists think the crest could have let the dinosaur cool down by connecting to its brain.

Behavioral hypotheses

Parasaurolophus might have used its crest to make low-frequency sounds to warn or talk to others of its kind. This idea comes from the shape of its nasal passages, which are similar to those of a swan. The crest could also have been used to recognize others of its species or to show off. The large eyes and possible skin frill on its neck might have made it even more noticeable.

Soft tissue frill

One scientist thought Parasaurolophus might have had a skin frill extending from its crest to its neck, like some modern lizards. This idea was popular in old artwork but isn’t strongly supported by evidence today.

Paleoecology

Parasaurolophus walkeri, from the Dinosaur Park Formation, lived alongside many other famous dinosaurs such as Centrosaurus, Chasmosaurus, and Styracosaurus. It shared its environment with predators like Gorgosaurus and Daspletosaurus, as well as other duckbilled dinosaurs. The area was a mix of rivers and floodplains, with a warm climate and lots of plants like conifers and ferns.

In places like New Mexico, Parasaurolophus lived with dinosaurs including Pentaceratops sternbergii and Stegoceras novomexicanum. The landscape was swampy and close to ancient shorelines. In Utah, Parasaurolophus shared its home with many different dinosaurs, such as Utahceratops gettyi and Gryposaurus monumentensis, along with various other animals like turtles and early mammals.