Hadrosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Hadrosauridae

Genus:Hadrosaurus

Species:Hadrosaurus foulkii

Introduction

The first nearly complete dinosaur skeleton discovered was that of Hadrosaurus foulkii, (“Foulke's Bulky Lizard”) in Haddonfield, New Jersey, in 1858. Ten years later, Hadrosaurus foulkii became the first nearly complete dinosaur skeleton ever to be mounted and presented in an exhibit. The skeleton was first exhibited at Philadelphia's Academy of Natural Sciences, where interest was so great that attendance grew by about 50 percent. This find touched off what became known as the “Bone Wars” between two famous paleontologists of the era, Edward Drinker Cope and Othniel Charles Marsh. In 1991, Hadrosaurus foulkii became the official state dinosaur of the state of New Jersey.

During the Cretaceous period, much of Asia, Europe, and North America were one continent, known as Laurasia. This region had once been part of the landmass known as Pangaea, which, over the course of the Jurassic period (201–145 million years ago), broke into Laurasia in the north and Gondwana in the south. The area of modern-day North America was split by a shallow sea, making the western half an island. It was during this period that seasons became more pronounced, offering more plants and flowers for herbivores. Trees such as maple, oak, and walnut developed as well.

Classification

In Linnaean taxonomy, hadrosaurs, which are also referred to as “duck-billed,” belong to the class Sauropsida, the members of which generally have long tails and necks, as well as strong and lightweight vertebrae. Hadrosaurs are also part of the order Ornithischia, which means “bird-hipped.” Other dinosaurs in this order are those with armor, such as ankylosaurs, and those with plates, such as stegosaurs. Hadrosaurs are further classed into the Ornithopoda infraorder, which comprised herbivorous dinosaurs with three-toed feet (similar to those of today's birds). Ornithopods are known to have existed predominately in the Northern Hemisphere, in areas such as modern-day North America, Asia, and Europe. Hadrosaurus is further classified in the Linnaean system as a member of the Hadrosauridae family.

Another classification system used by paleontologists is cladistics or phylogenetic classification, which classifies dinosaurs through shared physical characteristics and common ancestry into groups called clades. In a cladistic analysis, Hadrosaurus falls under the Hadrosauridae clade because of its dentition and hoof structure, and further under the Hadrosaurinae clade because of its flat head and solid bone crests. In general, hadrosaurs may have developed from a common ancestor, Iguanodon, about 100 million years ago, during the Cretaceous period.

Anatomy

Hadrosaurus was bipedal, meaning that it could stand on two legs. The back legs were larger than the forelegs, leading scientists to assume that the front legs were used only when the dinosaur was moving slowly or resting. American paleontologist Joseph Leidy, who first described Hadrosaurus, thought it stood browsing in the same way a kangaroo does when feeding. While the dinosaur's beak was toothless, its jaw featured many teeth.

Like all hadrosaurs, Hadrosaurus had a duckbill. Some scientists believe that Hadrosaurus also had an inflatable skin flap over its nostrils. Not only could this flap be enlarged to make a display, perhaps for courting or fighting, but it also might have produced a bagpipe-like sound.

Hadrosaurus foulkii had 28 vertebrae; 18 were tail bones, 7 were back bones, and 3 were cervical, or neck, bones. Standing upright, the dinosaur was as tall as a three-story building.

In part because researchers discovered Hadrosaurus in rocks near water or where water had once been, they originally thought that the species was amphibious. The tail was considered more of a rudder for steering during swimming. Later scientists, however, believe that Hadrosaurus was a land animal and that its stiff tail, which went straight back from the rear portion of the body, offered balance. What appeared to be a webbed hand were actually three fingers that joined in a thick pad, similar to that of a camel's padded “hand,” which supported the body when the animal was on all fours.

Intelligence

Slower-moving herbivores tended to fall lower on the EQ scale than their faster, carnivorous, predatory counterparts. However, the hadrosaurs as a group appeared 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

Hadrosaurus made nests for its eggs and hatched its young, probably in colonies. The babies remained in the nest for perhaps 8 or 9 months. Some research indicates that Hadrosaurus parents protected their young from predators and brought food to the nest.

Based on research of Maiasaura, a member of the Hadrosauridae family, scientists believe that females laid eggs in the nest, then covered them with sand, earth, or decaying vegetation. This mixture would heat up as the material decayed, just as a compost pile does, creating warmth for the eggs. Nests have been found that were used year after year. One or both parents probably brought food to the young.

Another theory is that the dinosaurs timed their breeding to coincide with the warmest time of the year, so that food would be available for both parents and newly hatched young.

Diet

The herbivorous Hadrosaurus has been referred to as the cow of the Cretaceous period. Its broad, horny snout had no teeth, but its cheeks contained hundreds of teeth, including replacement teeth, arranged in 40 to 60 rows known as dental batteries. The teeth were continually being ground down and replaced. Scientists believe that the rows of teeth allowed Hadrosaurus to masticate, or chew, leaves and branches, as well as tear them off. Both the upper and lower jaws could move sideways as well as up and down. Like squirrels, Hadrosaurus could store extra food in its cheeks.

Because they were herbivores, Hadrosaurus is thought to have had large digestive systems to help it digest the high-fiber foliage of shrubs and trees. Flowering plants, or angiosperms, developed during the Cretaceous period. Waterlilies and magnolias were some of the early kinds of flowering plants.

Behavior

Some species of hadrosaurids had ornaments on their heads. Researchers theorize that these may have served as weapons in combat or in mate competition. The crests may also have been part of courtship and mating rituals.

Hadrosaurus was possibly a herd animal, similar to large birds in flocks today. In the North American West, piles of bones belonging to a single species of closely related hadrosaurids may indicate that it lived in herds of both adults and young.

Habitat and Other Life Forms

Hadrosaurus foulkii lived in marshy areas along the Atlantic coast or in areas with shrubby plants. It could swim and may have spent time in the water. The first paleontologists believed that the dinosaur was a water creature.

More recent research suggests that the hadrosaurs could enter water to escape predators, but were terrestrial, or land-dwelling, creatures.

Other dinosaurs of the Cretaceous period included carnivores such as Tyrannosaurus rex. Dryptosaurus aquilunguis (the second almost-complete dinosaur skeleton discovered) was a carnivore found in what is now New Jersey, which preyed upon Hadrosaurus foulkii. Other plant-eating dinosaurs of the period included Triceratops.

In addition to the land-based dinosaurs, there were flying ones, called pterosaurs. One of the largest was Pteranodon, which had a wingspan of more than 30 feet. It cruised over bodies of water, seeing crabs, fish, mollusks, and insects. Other smaller flying creatures included bees and moths.

Research

In 1999, Tyler Lyson, a teenage paleontologist, found a so-called “dinosaur mummy” in North Dakota. The fossils of the dinosaur, a hadrosaur that has become known as “Dakota,” contained tissue and skin in a preserved, non-collapsed state.

A CT-scan on the fossilized remains revealed that the muscle mass of the dinosaur's rear was about a fourth larger than previously thought. A larger muscle mass means stronger legs, leading researchers to conclude that the animal, despite its size, moved faster than supposed. This speed would have helped it outrun such predators as Tyrannosaurus rex.

The dinosaur's skin showed some variation in scale size, leading scientists to suggest that the skin may have been multicolored, as is true of some reptiles today. These colors likely helped camouflage the dinosaur, further protecting it from predators.

In 2020, a team of international researchers discovered cavities and lesions on two vertebrae of a Hadrosaur skeleton found in Canada. The team deduced that the cavities were caused by a tumor, and created a reconstructed 3D image of the tumor and blood vessels leading to it. The image confirmed the likelihood that the tumor was Langerhans cell histiocytosis (LCH), a rare disease that typically affects young children. The discovery showed that the disease could span tens of millions of years and cross species, leading to new avenues of research into the evolution of such diseases.

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