Wednesday, November 30, 2016

Lambeosaurus reconstruction

Lambeosaurus (meaning “Lambe’s lizard”) is a genus of hadrosaurid dinosaur that lived about 75 million years ago, in the Late Cretaceous period (Campanian) of North America. This bipedal/quadrupedal, herbivorous dinosaur is known for its distinctive hollow cranial crest, which in the best-known species resembled a hatchet. Several possible species have been named, from Canada, the United States, and Mexico, but only the two Canadian species are currently recognized as valid.

L. lambei compared to a human by Dinoguy2

Lambeosaurus was belatedly described in 1923 by William Parks, over twenty years after the first material was studied by Lawrence Lambe. The genus has a complicated taxonomic history, in part because small-bodied crested hadrosaurids now recognized as juveniles were once thought to belong to their own genera and species. Currently, the various skulls assigned to the type speciesL. lambei are interpreted as showing age differences and sexual dimorphism. Lambeosaurus was closely related to the better known Corythosaurus, which is found in slightly older rocks, as well as the less well-known genera Hypacrosaurus and Olorotitan. All had unusual crests, which are now generally assumed to have served social functions like noisemaking and recognition.

Restoration of a crouched L. lambei by ДиБгд at Russian Wikipedia Tail and hands fixed by FunkMonk.

As in other lambeosaurines, the hollow crest would have formed a resonating chamber for its calls, amplifying them and making a distinctive sound in each species. The shape and patterning of the crest would also have helped individuals to recognize each other in the herd.

Lambeosaurus, best known through L. lambei, was quite similar to Corythosaurus in everything but the form of the head adornment. Compared to Corythosaurus, the crest of Lambeosaurus was shifted forward, and the hollow nasal passages within were at the front of the crest and stacked vertically. It also can be differentiated from Corythosaurus by its lack of forking nasal processes making up part of the sides of the crest, which is the only way to tell juveniles of the two genera apart, as the crests took on their distinctive forms as the animals aged.

Lambeosaurus was like other hadrosaurids, and could move on both two legs and all fours, as shown by footprints of related animals. It had a long tail stiffened by ossified tendons that prevented it from drooping. The hands had four fingers, lacking the innermost finger of the generalized five-fingered tetrapod hand, while the second, third, and fourth fingers were bunched together and bore hooves, suggesting the animal could have used the hands for support. The fifth finger was free and could be used to manipulate objects. Each foot had only the three central toes.

Skull of an adult Lambeosaurus lambei, AMNH. Photo by Ryan Somma

Some Lambeosaurus fossils display detailed impressions of the skin, showing that the skin of the body had a “pebbly” texture and that a weblike sheath of skin joined the fingers. When they were first described, these “webbed hands” were thought to prove the now-out-moded idea that duckbills were aquatic. The “web” actually enclosed a fleshy pad on the palm like that on a camel’s foot.

Lambeosaurus is the type genus of the Lambeosaurinae, the subfamily of hadrosaurids that had hollow skull crests. Among the lambeosaurines, it is closely related to similar dinosaurs such as Corythosaurus and Hypacrosaurus, with little separating them but crest form. The relationships among these dinosaur genera are difficult to pick out. Some early classifications placed these genera in the tribe Corythosaurini, which was found by David Evans and Robert Reisz to include Lambeosaurusas the sister taxon to a clade made up of CorythosaurusHypacrosaurus, and the Russian genus Olorotitan; these lambeosaurines, with Nipponosaurus.