Lambeosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Hadrosauridae

Genus:Lambeosaurus

Species:Lambeosaurus lambei

Introduction

Lambeosaurus is a genus of large herbivorous dinosaurs that lived in Late Cretaceous period North America, Europe, and Asia. A hadrosaurid, it was one of the most successful and widespread groups of herbivorous dinosaurs in the Mesozoic Era (251–66 million years ago). The type species, Lambeosaurus lambei, and its relatives are particularly known for the distinctive head crest, which has led to much speculation over its function and the presence of sexual dimorphism in dinosaurs.

In the Triassic period, when the dinosaurs appeared, the continents of the earth were united in a single land mass, called Pangaea. In the Jurassic and Cretaceous, Pangaea broke apart under the influence of tectonic forces, giving rise to the supercontinents Laurasia and Gondwana. Lambeosaurus and other members of its group were present in most of Laurasia but not found in Gondwana, suggesting that the group emerged from an ancestor that was isolated in Laurasia after the continents divided.

Classification

Scientists utilize two primary methods to classify organisms. Linnaean taxonomy, or systematics, creates categories based on overall physical similarity. An alternate system, called cladistics, attempts to create categories that better reflect the evolutionary relationships between species.

In the traditional Linnaean system, dinosaurs have long been divided into two orders based on pelvic structure: Ornithischia, or “bird-hipped,” and Saurischia, or "lizard-hipped." (Although in the twenty-first century some researchers challenged that longstanding division, it remained in wide use.) Lambeosaurus is considered an ornithischian. From there, taxonomists place Lambeosaurus in the family Hadrosauridae, popularly known as the “duck-billed” dinosaurs, which had bills for cropping vegetation, semi-bipedal movement, and teeth in their cheeks.

From a cladistic perspective, Lambeosaurus is part of the clade Ornithopoda, a group of ornithischians placed together because of various developments, including in the feet. Lambeosaurus is further divided into the clade Hadrosauria, because of its “duck bill,” teeth, and conformation of the metacarpal bones. It is considered the type genus of the clade Lambeosaurinae, the members of which have enlarged nasal cavities and hollow crests on their skulls. Paleontologists still sometimes differ in the exact placement of Lambeosaurus and its relatives in the hadrosaur family tree.

Early researchers often identified many different species of Lambeosaurus or even identified some specimens as completely different genera. However, many of these were eventually found to be different only due to age or sex. By the late twentieth century most paleontologists agreed only on two valid species, Lambeosaurus lambei and Lambeosaurus magnicristatus, though others have been proposed.

Anatomy

Lambeosaurus was a large herbivore, with an adult length of between 12 and 15 meters (29–49 ft) and standing about 2.1 meters (7 ft). On its hind legs Lambeosaurus could stand almost 6 meters (20 ft) tall. Paleontologists estimate that adult Lambeosaurus weighed between 6,000 and 6,500 kilograms (13,000–14,000 lbs).

Like all hadrosaurs, Lambeosaurus had robust hind legs and shorter forelimbs that were strong enough to support the animal's weight. Lambeosaurus had three toes on its rear feet and four fingers on its front hands, though the fourth finger was smaller and largely vestigial. All digits ended in blunt, hoof-like claws. All hadrosaurs had long tails, stiffened by bony struts reinforcing the vertebrae.

Lambeosaurus had a flattened bill with no front teeth. Its jaws contained rows of leaf-shaped teeth, which could be continually replaced as they were worn down by chewing rough vegetation. The pronounced head crest of Lambeosaurus varied in shape and size but was roughly “hatchet-shaped.” Skin impressions found on some hadrosaur fossils indicate that the animals were covered in pebbled scales.

Intelligence

Paleontologist James A. Hopson, from the University of Chicago, used the ratio of brain-to-body mass, called the encephalization quotient (EQ), to estimate the animal intelligence of dinosaurs. Most dinosaurs fall within a range of 0.1 to 2.0 on a scale that extends to an upper limit of 8.0, the approximate value calculated for the human brain. Hadrosaurs like Lambeosaurus fall within the range of 1.5 to 2.0, making them slightly less intelligent than many modern herding animals, like bison and camels, which paleontologists believe behaved similarly to hadrosaurs.

Many hadrosaur species were large and likely relied on size and group vigilance to avoid predators, thereby reducing the need for advanced cognitive abilities. Hadrosaurs may have had similar intelligence to many species of small birds or fowl, with sufficient intelligence to recognize and respond to cues from other members of the herd, helping to find food and avoid danger.

Reproduction and Population

Paleontologists believe that most dinosaurs were oviparous, or egg-laying animals. Paleontologists have found hadrosaur nests representing several species, some containing as many as twenty eggs, which were generally laid into an earthen nest built up from vegetation, soil, and other debris.

Paleontologists believe that hadrosaurs gathered into groups to lay their eggs, as multiple nests have been found in close proximity to one another. In addition, paleontologists have found egg fossils in nests that may represent several seasons of egg-laying, indicating that dinosaurs may have used the same nests during successive seasons.

Some paleontologists believe that the variation in nasal crests between specimens of Lambeosaurus might represent sexual dimorphism, a condition in which males and females of a species have different physical characteristics. If the species were dimorphic, the crest may have had a function in mating behavior. The crests may have been used to display fitness to potential mates or to compete for mating rights. The crests may also have varied in color to display an individual's readiness to mate.

Diet

Scientists believe that hadrosaurs were strict vegetarians. The flat, wide bill of Lambeosaurus was most likely used to crop vegetation, while the battery of teeth in the animal's cheeks allowed it to masticate its greens before passing them to the stomach, thereby speeding digestion.

There was a wide variety of vegetation available in Late Cretaceous Laurasia, including many species of ferns, tree ferns, cycads, and conifers. Hadrosaurs had wide bodies, suitable for housing a large, complex system of intestines, which were often necessary for digesting thick plant fibers.

Behavior

Fossil beds have revealed hadrosaur fossils grouped together, which some scientists suggest indicates group behavior. Alternately, the animals may instead have gathered in chaotic groups around a shared food source. Paleontologists have also found fossilized footprints left by hadrosaurs, indicating individuals of multiple sizes and ages. These fossilized trackways indicate that some hadrosaurs may have traveled together.

The function of the nasal crest on lambeosaurinae is also a source of debate among paleontologists. The crests were an extension of the nasal passages, and some scientists believe they were used to produce deep sounds. Some animals use sound to stay in contact across distances, or to demarcate territorial boundaries. Alternatively, the crests may have had a reproductive function, using color, sound, and visual cues to aid in mating behaviors.

Habitat and Other Life Forms

In the Late Cretaceous, vast portions of North America were covered in a shallow inland sea, surrounded by shallow flood plains and a variety of forest habitats. Gymnosperms like conifers, cycads, and ferns were the most abundant type of vegetation in the Cretaceous, though the first angiosperms, or flowering plants, were beginning to spread throughout the environment.

There were a wide variety of reptiles, amphibians, and small mammals living in Late Cretaceous Laurasia, many resembling extant species. The first birds had evolved by this time, though flying reptiles called pterosaurs were the most abundant flying vertebrates.

There were several species of hadrosaur living in North America, including Maiasaura and Anatotitan. In addition, North America boasted a variety of ceratopsians or “horned dinosaurs,” like Triceratops and Styracosaurus, which formed one of the other most abundant herbivore groups. Other herbivore groups included iguanodontids, pachycephalosaurids, and ankylosaurs. There were a number of predatory dinosaurs in the area as well, including several species of dromaeosaurs, sometimes called “raptors,” like Utahraptor and Dromaeosaurus. There were also larger carnivores present, including the large theropod Tyrannosaurus .

Research

Lambeosaurus was discovered in Alberta, Canada, in 1902 by Canadian paleontologist Lawrence Lambe. He originally placed it within another proposed genus, Trachodon, sometimes used as a “catchall” genus for fragments of fossils that were poorly defined. Juvenile specimens of Lambeosaurus from Canadian fossil sites were also initially interpreted as a separate species, until they were later joined with the adult specimens. The genus was separated out and named Lambeosaurus (after Lawrence Lambe) in the early 1930s. Over the years a wide variety of proposed Lambeosaurus species were reduced to only a few, as different size specimens and those with different crest shapes were interpreted as simply different forms of the same species.

Because specimens of Lambeosaurus have a wide range and because some fossil beds have produced juvenile individuals, Lambeosaurus has been instructive in the ongoing effort to create an accurate picture of hadrosaur behavior. Scientists have studied the bones of juvenile Lambeosaurus to determine growth rates, a factor in determining the life expectancy and breeding patterns of the dinosaurs.

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