A common theme of evolution is that in different geological epochs, different species of animals, as a rule, occupy the same ecological niches. Today, the niche of the “herbivore four-legged” is filled with mammals such as deer, sheep, horses and cows; 75 - 65 million years ago, near the end of the Cretaceous, it was occupied by hadrosaurs (duck-billed dinosaurs). These four-legged small-brain plant eaters can (in many ways) be considered the prehistoric equivalent of cattle, but not ducks, which belong to a completely different evolutionary branch.
Given the numerous finds of their fossil remains, it is likely that in the later stages of the Cretaceous, there were more hadrosaurs than representatives of any other type of dinosaurs (including keratopsians, tyrannosaurs and other predators). These creatures roamed the forests and plains of North America, Europe and Asia, part of them gathered in herds, consisting of hundreds or thousands of individuals.
Anatomy
The description of the duckbill dinosaurs indicates that they got their name “hadrosaurus” from the Greek word for “big lizard”. They were far from the most attractive dinosaurs ever walking on earth. These plant eaters were distinguished by thick, squat torsos, massive inflexible tails, hard beaks and numerous teeth (up to 1,000 in some species), intended for chewing hard vegetation. Some of them (lambeosaurinae) had crests on the tops of their heads. Like cows and horses, duckbill dinosaurs (photo) grazed on four limbs, but even larger, multi-ton species were able to clumsily run on two legs, fleeing predators.
It is possible that they had pads on their feet, similar to those that camels have.
In some species, the teeth could be placed in six rows inside the mouth, and each row consisted of 45-60 teeth. Moreover, in the event of a breakdown or loss, new ones could grow from them.
Dimensions
Judging by the appearance of the duckbill dinosaurs, they were the largest of all ornithopods. Despite the fact that they technically belong to this infraorder, which also included iguanodons and tenontosaurs, it is rather difficult to draw a clear line between the most developed ornithopods and the earliest real hadrosaurs. Most duck-billed dinosaurs, including anatotitans and hypacrosaurs, weighed about several thousand kilograms, but some, like shantungosaurs, reached really huge sizes - about 20 tons, or ten times more than a modern elephant!
Platypus dinosaur lifestyle
They seem to have more in common with modern cows and horses than just the habit of grazing (although it is important to understand that grass in the Cretaceous has not yet evolved; rather, hadrosaurs have eaten undersized plants). At least some of them, such as the Edmontosaurus, roamed the forests of North America in large herds, which was a form of protection against predators. The giant curved crests on the backs of hadrosaurs, such as haronosaurs and parasaurolophus, were probably an individual trait that distinguishes the individual from other members of the herd. Studies have shown that with their help it was possible to make loud sounds. The combs may have performed an additional function during the mating season.
The Mayazavr, one of the few dinosaurs named after the female, and not the male of the genus, is a particularly important representative of hadrosaurs due to the large nest found in North America, in which the fossilized remains of adults and young animals, as well as numerous eggs located in its paws, are preserved. It is clear that this “good mother lizard” (its name is translated) closely watched their children even after they hatched, so it is possible that other duck-billed dinosaurs did the same.
Hadrosaurs probably spent most of their day on land, but lived close to the water. They migrated to nests to lay eggs. It is assumed that the eggs maintained their temperature due to the vegetation located in the nest.
Evolution
Hadrosaurs are one of the few dinosaur families that lived completely in the same historical period, from the middle to the late Cretaceous. Other species, such as tyrannosaurs, also flourished at the end of the Cretaceous, but there is evidence that their distant ancestors lived in the Jurassic. Some of the first representatives of the duckbill dinosaurs testify to the mysterious mixture of the hadrosaur and iguanodon traits; one late genus, the telmatosaurus, retained its iguanodon-like profile even at the final stages of the Cretaceous, possibly because this dinosaur was isolated and cut off from the main stream of evolution.
Prevalence
By the end of the Cretaceous, duckbill dinosaurs were the largest group, an integral part of the food chain, as they consumed the dense vegetation of North America and Eurasia, and they themselves were eaten by predators and tyrannosaurs. If these creatures did not disappear 65 million years ago, it is quite possible that some of the representatives of this species could develop to truly gigantic proportions, for example, like brachiosaurs.
Types
The duckbill dinosaurs are divided into two subfamilies.
Representatives of hadrosaurids (Hadrosauridae), which included mayasaurs, shantungosaurs and edmontosaurs, did not have a crest on the skull. The subfamily Lambeosaurids (Lambeosaurinae), which included parasaurolophs and Lambeosaurs, was distinguished by the presence of a crest.
Differences in appearance
One of the dinosaurs, which served as a kind of connection between the smaller bipedal ornithopods and the larger hadrosaurs, was the iguanodon, who lived in the early Cretaceous, about 125 million years ago. He moved on four limbs and had a rather large horn on his nose.
Researchers suggest that in some species, the crest on the head was fleshy, somewhat reminiscent of the crest of a rooster. But since such soft tissues are rarely preserved, there is no exact information about it.
Other species of duckbill dinosaurs had bone crests. They were hollow, and their exact purpose is still unknown, although scientists have some theories. Many paleontologists believe that they amplified the sounds made by the dinosaur. Others believe that they served to attract partners. They could also be a sign of maturity, as the skulls of smaller, younger dinosaurs have shorter crests.
Archaeological finds
The Grizzosaurus is one of the few dinosaurs that have been discovered with the remains of the skin, which allows scientists to better understand how they looked in life. They had a number of trapezoidal spines located on the back along the spine. Well-preserved remains of the edmontosaurus have also been found, including fossilized “mummies,” which contained not only skin but also muscle tissue.