Parasaurolophus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Hadrosauridae

Genus: Parasaurolophus

Species: Parasaurolophus walkeri

Introduction

As a family, hadrosaurs have been well-preserved and remain one of the best known and most thoroughly studied dinosaurs. Parasaurolophus is considered one of the more rare and interesting finds among this family. Several specimens for three distinct species—P. walkeri, P. tubicen, and P. cyrtocristatus—have yielded complete skulls and nearly complete skeletons. Parasaurolophus walkeri is the type species and is known from only one specimen. Parasaurolophus cyrtocristatus, which is the smallest species, is known from more than one potential specimen.

All hadrosaurs are notable for their remarkable crests and unique duckbilled facade, but Parasaurolophus stands out even among this company. Parasaurolophus bears a hollow crest that extends up to 1.5 meters (5 ft) back from its skull, passing over its shoulders and giving it an easily recognizable feature among the herds of herbivores with which it likely traveled. In addition, this long cranial tube has been compared to a trombone by many for the deep, resonant sounds it is believed to have made.

Classification

Paleontologists generally use two systems for dinosaur taxonomy. The hierarchical Linnaean classification system, developed by Carl Linnaeus in 1735, consists of different tiers of classification (class, order, family, genus, and species) based on shared characteristics within each grouping. Species, the lowest tier, is based on the most specific shared traits. Additional sub-categories were added later.

According to Linnaean taxonomy, Parasaurolophus is classified under the order Ornithischia. One of two orders of dinosaurs, the ornithischians were known for their bird-like hip structure, with its pelvic bone pointed down and back towards the tail. Dinosaurs in this order also tended to be herbivores and to have hoof-like claws on their feet and beak-shaped mouths. At the same time, the traditional division into the two orders of Ornithischia and Saurischia was a subject of scientific debate by the third decade of the twenty-first century.

The Ornithischia order breaks down into several dinosaur families according to more specific physical characteristics. Parasaurolophus falls under the Hadrosauridae family because of its flat, duck-billed skull; toothless beak with numerous teeth set back in the cheek; four-fingered hands; and notable cranial crest. Parasaurolophus is distinct as a species for the hollow, tube-like crest that extends back from its skull. The type species, Parasaurolophus walkeri, was named for Sir Bryon Edmund Walker, an important early patron of the Royal Ontario Museum, which sponsored the excavation in which the fossils were unearthed.

Scientists also use another classification system, called phylogenetic or cladistic classification. This system classifies animals in family trees, called cladograms, grouped by common ancestry. Each split in the tree creates a new group based on shared physical traits. Within cladistics, Hadrosauridae comprise their own clade, or branch on the dinosaur family tree. This means that all hadrosaurs, including Parasaurolophus, share a common ancestor within the larger family of ornithopods.

The Hadrosauridae clade branches into smaller, more specific subfamilies. Parasaurolophus belongs in the Lambeosaurinae clade, which is known for its hollow crests. This clade also includes Corythosaurus, Hypacrosaurus, Lambeosaurus, and Tsintaosaurus. Some paleontologists believe that Parasaurolophus may form a smaller clade with Charonosaurus, the only known fossils for which come from China.

Anatomy

Parasaurolophus displayed many of the anatomical features common to the hadrosaurs. As one of the larger hadrosaurs, Parasaurolophus had a typically large torso; long, pointed tail; and curving neck, as well as shorter forelimbs than hind. The skeletal structure of its four legs indicates that Parasaurolophus was both bipedal and quadrupedal. It likely spent much of its time on four limbs but rose into a bipedal stance for faster travel. Its forelimbs were also unique in that its hands lacked thumbs.

Parasaurolophus possessed the characteristic duckbilled head of the hadrosaurs. It had a long skull that tapered to a narrow snout capped in a beak-like, toothless mouth. Its small plant-eating teeth were housed farther back and laterally, in rows within its cheeks. Like other hadrosaurs, Parasaurolophus had hundreds of teeth.

The most distinctive feature of Parasaurolophus was undoubtedly its large cranial crest, which extended up to 1.5 meters (5 ft) back from its head. The tube-like crest was narrow, curved, and hollow, extending from the dinosaur's nasal passages. This feature made the crest as much an instrument as an ornament. Paleontologists believe that the crest functioned both as a visual recognition device, enabling Parasaurolophus to quickly identify members of its own species within a larger mixed-species herd, and as an auditory tool. The hollow chamber, which varied in size and shape, likely produced unique sounds that enabled Parasaurolophus to signal one another and communicate in other fashions.

Dinosaurs have generally been regarded as cold-blooded animals, like modern lizards, though the term “cold-blooded” is deceptive. Modern lizards are ectothermic, meaning that they rely on the sun and other environmental factors to warm their bodies. Though science has traditionally held dinosaurs, specifically non-avian dinosaurs, to be ectothermic, evidence suggests that some might have been endothermic, meaning that they could heat their bodies from within by consuming food. Scientists continue to debate whether hadrosaurs such as Parasaurolophus might have been ectotherms, endotherms, or something in between. Many scientists believe that the growth rate of hadrosaurs indicates that they were endothermic.

Intelligence

Slower-moving herbivores tend to fall lower on the EQ scale than their faster, carnivorous, predatory counterparts. However, the hadrosaurs as a group appear to have had larger brain-to-body mass ratios and keener senses, placing them higher on the intelligence scale than most other herbivores. They likely ranked between 0.8 and 1.5.

Reproduction and Population

Fossil evidence for Parasaurolophus is limited and rare compared to the abundance of fossil finds for its many hadrosaur relations. As of 2020, Parasaurolophus specimens had been found only in the western United States and Canada. However, hadrosaur fossils, in general, have been found on five of seven continents—none had been unearthed in Africa or Australia as of 2020—and constitute one of the most represented of the dinosaur families in the fossil record. Such large fossil fields indicate that the hadrosaurs existed in great numbers and thrived during the Late Cretaceous period (99–66 million years ago).

Most paleontologists believe that dinosaurs, including hadrosaurs such as Parasaurolophus, were oviparous. This means that they reproduced by laying eggs. In fact, the fossil remains of hadrosaurs have contributed a great deal to the study of dinosaur reproduction and nesting. Hadrosaur nesting sites have yielded important egg finds, demonstrating not only the oviparous nature of some (if not all dinosaurs), but also the nesting tendencies of certain genera. Group nesting sites suggest that herds laid and watched over eggs together and shell and skeletal evidence reveals that hatchlings likely remained in the nest for a period of time and were fed by their parents or other adult hadrosaurs. Some geographic evidence suggests that hadrosaurs traveled to specific nesting sites to lay and tend their eggs and that these sites were used by cycling groups of parents that return to the same ground each year.

The different sizes of fossils found for Parasaurolophus have suggested to some scientists that the female members of the species were smaller than the males and had smaller head crests. Paleontologists have also suggested that the visual and auditory functions of the tube-like crest may have served to attract potential mates.

Diet

Like other hadrosaurs, Parasaurolophus was a plant-eater. Its numerous but small teeth, set back in its cheeks rather than in the forefront of its mouth, were designed for chewing a variety of foliage, including leaves, seeds, pods, pine needles, and fruits. Its beak-tipped mouth would have served well for tearing and gripping such food. Living in the Late Cretaceous, Parasaurolophus would have found an abundance of vegetation. Its diet most likely consisted of ferns, gymnosperms (seed plants such as conifers and cycads), and perhaps the newly evolved flowering angiosperms. The skeletal structure and sometimes quadrupedal stance of Parasaurolophus indicate that this dinosaur likely grazed on ground foliage and other low-lying vegetation within its reach. Like most herbivores, Parasaurolophus probably spent a great deal of time looking for and consuming food.

Behavior

Though an abundance of fossil evidence exists for many hadrosaurs, the fossil record for Parasaurolophus is insufficient for scientists to draw firm conclusions regarding the behavior of this species. Paleontologists believe that most hadrosaurs, however, were highly socialized herd animals. Dozens of fossils have been found in collective sites for other hadrosaur species. These fossils as well as their widespread geographic locations indicate that hadrosaurs traveled in large groups and migrated across the continents. Some hadrosaurs are even believed to have traveled in groups numbering in the hundreds.

Most migratory dinosaurs, such as hadrosaurs, likely moved from place to place in search of food and may have traveled with other plant-eating, herding species. Though more fossil evidence is needed, it seems likely that Parasaurolophus was a fairly gregarious species.

Habitat and Other Life Forms

As of 2020, all fossil evidence for Parasaurolophus had come from western Canada and the United States, indicating that the species thrived in this region during the Late Cretaceous period. However, its fellow hadrosaurs are known to have lived across the globe in great numbers. In Canada and elsewhere, the Late Cretaceous was a time of great change, including plant and animal diversification. The climate differed markedly from that of the same region today. The climate was far warmer, likely sub-tropical, and the land was more likely covered in thick forests and swamps.

By this time, the vast supercontinent of Pangaea had split into two smaller supercontinents, Gondwana and Laurasia. Throughout the Late Cretaceous, tectonic change continued, with the breaking apart of Laurasia into smaller continents. These tectonic shifts brought great changes to the climate and landscape. Species became more isolated even as new plants and animals emerged. The Late Cretaceous would prove to be the final period of dinosaur life on earth, and dinosaurs shared the land with a diverse variety of insects, birds, mammals, amphibians, and flora.

Evidence suggests that Parasaurolophus and its relations benefited from the sudden flourishing of flowering plants across the globe. Their success at foraging on angiosperms and other plant life may have contributed to the decline in some other herbivore species. They likely roamed the forests and possibly the grasslands and wetlands of their environment.

The hadrosaurs of western North America shared their landscape with many other great and familiar dinosaurs of the time—including their fellow herbivores, the horn-frilled ceratopsians, including Centrosaurus and Styracosaurus, and their fierce predators, the tyrannosaurs, which included Albertosaurus, Daspletosaurus, and Appalachiosaurus.

Research

Canadian paleontologist William Parks unearthed the first fossils for the genus Parasaurolophus in 1920. The complete skull and nearly complete skeleton were discovered in the Dinosaur Park Formation near Alberta, Canada, a rich fossil site that has also yielded dozens of other hadrosaurs and many other dinosaur species. Parks identified this fossil as a new species of hadrosaur and named it Parasaurolophus walkeri. Fossils for Parasaurolophus walkeri may also have been found in the Hell Creek Formation of Montana, but data remained inconclusive.

Around the same time, additional fossils from the genus Parasaurolophus were unearthed in the Lower Kirtland Formation of New Mexico by amateur paleontologist Charles Sternberg. This new discovery consisted of skull and skeletal remnants that scientists believed belonged to up to three specimens. A decade later, Swedish paleontologist Carl Wiman named the fossils a new species, Parasaurolophus tubicen.

Further Parasaurolophus fossils were discovered in the Kirtland Formation of New Mexico and identified by American paleontologist John Ostrom as a third species, Parasaurolophus cyrtocristatus, in 1961. (Ostrom is renowned for advocating that dinosaurs were more like large, flightless birds than lizards, and he was an early proponent of this revolutionary dinosaur-bird connection.) In 1979, more fossils for Parasaurolophus cyrtocristatus were located in the Kaiparowits Formation in Utah. Together, these finds included parts of a skull and a nearly complete skeleton.

The name Parasaurolophus itself means “near Saurolophus” referring to another hadrosaur species to which Parasaurolophus was believed to be closely related. (Saurolophus itself means “lizard crest.”) Two species were discovered for Saurolophus, the first in the Horseshoe Canyon Formation in 1912 and the second in the Nemegt Formation of Mongolia in 1952. Thorough investigation of the fossils revealed that Parasaurolophus predated Saurolophus by up to 5 million years. Parasaurolophus was also found to possess a far more unique and extravagant head crest.

In 2013, a paper published in the journal PeerJ announced that bones of a baby hadrosaur discovered in 2009 by a high school student within the Kaiparowits Formation in Utah belonged to Parasaurolophus. Following a years-long process of excavation and lab analysis, it was crucially considered the most complete skeleton of the genus uncovered up to that point and, as it was believed that the dinosaur had been approximately twelve months old when it died, it provided greater information about the development of Parasaurolophus, particularly regarding its crest. Also in the second decade of the twenty-first century, some scientists continued to focus on learning more about the types of sounds such hadrosaurs likely emitted, with one team conducting a study using a computed-tomography scanner to digitally analyze the Parasaurolophus crest.

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