name: Prosaurolophus time: Late Cretaceous locality: North America (Alberta) size: 26 ft/8 m long
Prosaurolophus was a typical member of the hadrosaurine group of hadrosaurs — those duckbills with solid, bony crests on their heads. Its skull was similar to that of one of the flat-headed duckbills, such as Anatosaurus (see p. 149). But the nasal bones were ex-tended into a low crest of bone that ran from the tip of the broad, flat snout up to the top of the head, where it was developed into a small, bony knob.
Since this crest became more pronounced in relatives of Prosaurolophus, this duckbill may have been ancestral to later members of the family, such as Saurolophus (below).
name: Saurolophus time: Late Cretaceous locality: North America (Alberta and California) and Asia
(Mongolia) size: 30 ft/9 m long
The face of this large duckbill swept upward in a graceful curve, from the broad, flattened snout to the tip of a solid, bony, hornlike crest that sloped backward from the top of its head. The size of the crest varied between species of Saurolophus. The Asian species had a larger crest than its North American relative and a correspondingly larger body size, of about 39 ft/12 m long.
The crest was an extension of the nasal bones, and the nasal passages would have run through it. This has led some paleontologists to think that there was a mass of nasal tissue which could have been inflated, and used to produce bellowing or honking sounds through the nose. The bony crest would have acted as a support for this inflatable sac, so increasing its area and, hence, its efficiency. Since hadrosaurs lived in herds, such sounds would have been an effective means of communicating with each other, especially over a distance.
name: Tsintaosaurus time: Late Cretaceous locality: Asia (China) size: 33 ft/10 m long
A unicorn-type horn grew from the top of this Chinese duckbill's head, giving it a bizarre appearance quite unlike that of any of its relatives. The tall column of bone pointed straight up from between the eyes. Its tip was expanded and notched. And there was a connection between the base of the crest and the nostrils.
These facts have led some paleontologists to believe that there may have been a flap of skin attached to the horn, or maybe even stretched between the tip of the horn and the beak. This flap could have been inflated like a balloon, and used as a signaling device between members of the herd, either for courtship or for threatening rivals. It may even have been brightly colored, in which case it would have made a spectacular display for either purpose — attracting or repelling.
Other paleontologists, however, think that the horn from the original specimen of Tsintaosaurus found in China was wrongly mounted on the reconstruction of the animal, and that it should point backward, as in Sauroh' phus (above).
name: Corythosaurus time: Late Cretaceous locality: North America (Alberta and Montana) size: 30 ft/9 m long
A spectacular semicircular crest decorated the head of this large, North American duckbill, which weighed almost 5 US tons/4.5 tonnes. The crest rose steeply from just in front of the animal's eyes into a tall, narrow fan shape (about 1 ft/30 cm high) that curved down to the back of the head.
Several sizes of crest have been found in different specimens of Corythosaurus. This could reflect different species of this duckbill, or more likely, it could show d ifferent growth stages of the same species, with juvenile specimens having much smaller crests than adults. There may even have been a size difference between the sexes, with full-grown males having the largest crests.
Corythosaurus was a typical member of the lambeosaurine group of hadrosaurs — those duckbills with hollow crests on their heads. (Solid head crests characterized the hadrosaurine duckbills, see pp. 146-149, 150, 152.) As a group, the hollow-crested types seem to have evolved in North America, and been largely confined to the western part of that continent. Some species have also been found in eastern Asia, which fact lends support to the theory that western North America and eastern Asia were joined together in Late Cretaceous times as one land mass, "Asiamerica," and surrounded by shallow continental seas (see pp. 12-13).
The domed crest was made up of the greatly expanded nasal bones. The hollows inside the crest were the actual nasal passages, which ran up into the crest and looped back down into the snout. Several theories have been proposed for such an arrangement, some of them more likely than others. The old notion, for example, that hadrosaurs were aquatic animals, led to the belief saurolophus
prosaurolopifl tsintaosaurus saurolophus tsintaosaurus that the crest, with its series of hollow tubes, was some kind of snorkel, which allowed the animal to breathe air while its mouth and nostrils were submerged. Another theory stated that the crest acted as an air reservoir, so that the duckbill could draw on its supply while swimming or feeding underwater.
It is now known that the duckbills were well-adapted land animals. They were also gregarious and lived in herds, browsing in the forests on tough pine needles, magnolia leaves, seeds and fruits of all kinds. When threatened by predators such as Tyrannosaurus, they could sprint away on 2 legs; they may even have taken to water to escape.
Several more likely explanations exist for the hollow crest, and it is quite possible that it served some or all of the proposed functions. First, the hollow crest with its convoluted tube system could have been used as a vocal resonator — like the pipe of a trombone — to produce sounds for communication with the rest of the herd. These sounds could have been made for a variety of purposes — to warn other members in the herd of danger, to win a mate or discourage a rival, and for species-recognition between groups.
The results of recent research in the USA seem to support this theory. An exact model of a lambeosaur's crest was constructed, and experiments show that these duckbills could have produced a kind of foghorn sound from such a structure. These booming, resonant notes would have been heard over wide distances, and provided these forest-dwellers with an effective means of communicating between themselves and other herds. The postulated inflatable nasal sacs on the faces of the flat-headed, solid-crested duckbills (in the hadrosaurine subfamily) probably served the same purpose.
Another theory proposes that the prosaurolopifl
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