Hadrosaurs are a unique group of dinosaurs that are divided into two subfamilies: the crested dinosaurs (lambeosaurines) and the duckbills (hadrosaurines). All hadrosaurs are ornithopods (bird-hipped dinosaurs), meaning their hips are positioned like a birds, enabling them to stand upright. Hadrosaurs from later periods developed a slight curve in their spine to better facilitate grazing, giving them a slight stoop when they stood on their hind legs. They were able to walk on all fours, although their front legs were considerably shorter than their hind legs. Hadrosaurs are easily recognized by their distinctive facial features: some form of head crest in the crested dinosaurs, and a flat, sloped mouth resembling a ducks in the duck-bills’ case. While each group of hadrosaur has twenty or so different species in it, this article will only look at a few species from each subfamily.

The hadrosaurs were herbivorous, and lived during the mid-late Cretaceous. Coprolites (fossilized dino droppings) show that hadrosaurs ate a variety of leaves and twigs, mosses and fungi, and probably the tiny invertebrates that inhabited this flora. Hadrosaur fossils have been found throughout Europe, Asia and North America.

Crested Hadrosaurs − Lambeosaur, Corythosaurus, and Parasaurolophus

The crested dinosaurs are still puzzling scientists today: exactly what was the purpose of the dinosaurs’ crests? Many hypotheses about the crested dinosaurs’ elaborate headgear, which connected to the animal’s nasal cavity, have been put forward. That the crest was used mainly for show, i.e. to attract a mate; as a resonating chamber to project the animals’ calls further; as a smell enhancer; a thermoregulator, controlling its body temperature; as a means of storing extra air for underwater foraging. All seem likely, yet there is no conclusive evidence supporting any one hypothesis.

Lambeosaur

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The Lambeosaur (Lambe’s Lizard) hailed from the late Cretaceous (75-76 mil. Years ago), and as such is one of the hadrosaurs with a sloping backbone and the means to walk as a biped or quadruped. Its size ranged from 30-50 feet, nose to tail. Lambeosaur was named after Lawrence Lambe, the man who studied Lambeosaur and other hadrosaurs extensively. Studies of Lambeosaur skulls suggest that it was diurnal, and had good vision, as well as sensitive hearing. Lambeosaur had a narrow beak-tipped mouth, allowing it to be fairly selective and pick what parts of the plant it wished to eat. Lambeosaur’s crest resembles a misshapen L: there is a rounded crest on the top of its head, which did not finish growth until the animal matured; and then a thinner crest portion that points backward at a ninety degree angle. It is thought that Lambeosaur spent much of its time in or near the water, due to its weak hip structure and also the long, narrow tail which may have aided swimming. Of the Hadrosaurs, Lambeosaur was the largest.

Corythosaurus

core-ITH-o-sore-us

Corythosaurus (helmet lizard) is very similar in appearance to the Lambeosaur. As many of the hadrosaurs who lived during the late Cretaceous, corythosaurus’ spine was also sloped, although its nose to tail length was only around 35 feet. The corythosaurus’ crest is slightly more rounded where the lambeosaurs’ is more wedge shaped. The corythosaurus did not have the extra protruding piece of crest at the back of its skull, either. While corythosaurus appeared to have webbing in between its feet, this actually turned out to be padding, like a dog’s, only thinner. This, and the fact that corythosaur fossils were found in places that were not near large water sources, suggested that corythosaurus did not spend its days frequenting water holes. Corythosaurs had beaks, although their mouths were wider than that of the Lambeosaur. The first corythosaur fossil, found by Barnum Brown in Canada, was complete, and is it wasn’t completely fossilized, it was even possible to see the type of skin the animal had. Unfortunately, while en-route to the U.S., the ship the fossil was on was sunk by the Germans during WWI.

Parasaurolophus

par-a-saw-RAWL-o-fuss

The Parasaurolophus (near crested lizard) is another curved spine hadrosaur from the late Cretaceous. It’s easy to distinguish from the Lambeosaur or Corythosaur. Parasaurolophus’ crest pointed backwards and was long, thin, and slightly curved. Like the corythosaurus, their mouths were wide If you’ve ever seen the cartoon The Land Before Time, you’ll note that Ducky is a Parasaurolophus. Parasaurolophus was about the size of Corythosaurus, averaging 30 feet. The areas that its fossils have been found, Dinosaur Park Formation in Alberta, Canada, suggest that Parasaurolophus lived near rivers and lakes, surrounded by plenty of greenery. Complete skeletons of Parasaurolophus have not been found, but it has been suggested that crest size of these dinosaurs relates to sex and age, where females and juveniles would have shorter crests than male or mature Parasaurolophus.

Duck-billed Hadrosaurs − Maiasaur, Edmontosaurus and Hadrosasurus

While the crested hadrosaurs all had “duck bills” in addition to their crests, the duck-billed hadrosaurs only had duck bills, no resplendent crests to accompany them. Except for this, they are much the same as the crested hadrosaurs.

Maiasaur

MY-uh-sore

As its crested relatives, Maiasaur lived during the late Cretaceous. Maiasaur fossils have been found in Montana. The dinosaur grew up to 23 feet, and could also walk either bipedally or on all fours. Maiasaur did have a small crest in front of its eyes, but nothing that would put it into the crested hadrosaur group. This dinosaur’s name means Good Mother Lizard. Many depictions of Maiasaur show it tending to a nest of hatchlings. The Maiasaur was so named because nests with Maiasaur eggs and hatchlings were discovered. This was proof that dinosaurs cared for their eggs and young, not just leaving their eggs in logs as lizards of today do. This was good news for the baby Maiasaur, because according to fossil evidence, young Maiasaur legs were not capable of supporting the baby’s body weight. Fossil evidence also shows that Maiasaur lived in herds, and probably had “nurseries” for the baby dinosaurs.

Maiasaur nest

Edmontosaurus

ed-MAWNT-o-sore-us

Edmontosaurs are another dinosaur from the late Cretaceous, with a curved spine enabling them to walk both upright and on all fours. They were some of the largest hadrosaurs, reaching a length of 43 feet. Edmontosaurus is named after the location it was first discovered: the Edmonton Formation in Alberta, Canada. Its fossils have been found throughout Midwestern North America as well though. Fossilized skin impressions of Edmontosaurus show that its hide resembled that of the modern-day Gila monster: a pebbly, or beaded, texture. Like the Maiasaur, Edmontosaurus is thought to have been a herd animal, staying close to coastal areas (not necessarily swampy). Isotopes found in teeth remains suggest that Edmontosaur might have been a migrating dinosaur, moving in season with its food of choice. Like many of its fellow hadrosaurs, the teeth of Edmontosaurus were constantly being replaced. Grinding down tough plant fiber is hard work for just one set of teeth. Edmontosaurus also had fleshy “pads” on its feet, for added protection when walking (contrary to the early hypothesis, which suggested these pads acted as webbing for swimming).

Iguanodon

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Iguanodon thumb spike

Perhaps a more familiar dinosaur, Iguanodon is known for the thumb spikes on its fore-feet. The first life-size rendition of an Iguanodon shown at the Crystal Palace in London, in the mid 19th century, is famous for having its thumb spikes mistakenly placed on its nose. It’s still not certain what purpose this spike served, although increased dexterity has been suggested. If this dinosaur’s name sounds strikingly familiar to the modern iguana, this isn’t a coincidence. Iguanodon means “iguana tooth.” Iguanodon enjoyed a long period of existence, thriving from the early Jurassic to the late Cretaceous. Average size was around 32 feet, although some species could reach 42 feet. Iguanodon’s duck bill isn’t anywhere near as pronounced as Edmontosaurus, but its lower jaw has a scoop to it that paleontologists are still trying to determine the exact purpose of.

Fun Reading

There are numerous representations of what hadrosaurs might have looked like. If you’re looking for a colorful and imaginative depiction of them, read James Gurney’s Dinotopia, and its two sequels, The World Beneath and Journey to Chandara. While these books do have pictures in them, they are by no means picture books only meant for youngsters. There is a substantial story and plot, and the dinosaurs are beautifully drawn and colored. Most of the dinosaurs above are featured at some point in Gurney’s series.

Sources

http://www.dinosaurfact.net/cretaceous/Corythosaurus.php

http://landbeforetime.wikia.com/wiki/Parasaurolophus

http://www.answers.com/topic/maiasaur