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Last updated on April 24, 2014 at 17:35 EDT

Altirhinus

Altirhinus, meaning “˜high snout’, is a genus of iguanodontian ornithopod dinosaur from the Early Cretaceous Period (125 to 100 million years ago) of Mongolia. It is known from one species (A. kurzanovi), which honors Russian paleontologist Sergei Kurzanov who discovered the specimen in 1981. It was discovered in the Khukhtek Formation in the Dornogovi Province of Mongolia.

Several specimens of A. kurzanovi from different age groups and sizes have been found, all in 1981. The holotype is a well preserved partial skull and pieces of hands, feet, shoulder and pelvis. A second skull was found along with some ribs, vertebrae, and a complete forelimb. A third specimen had limb bones and a series of 34 tail vertebrae from a smaller individual. Two even smaller skeletons were found nearby, presumably of juveniles.

Altirhinus was originally referred to as the species Iguanodon orientalis, first described in 1952. However, it has been proven that I. orientalis has no distinguishable features with the discovered specimens, and as such the 1981 specimens have been named Altirhinus kurzanovi by paleontologist David B. Norman in 1998.

Altirhinus was herbivorous. When walking and running it would have been bipedal. It probably became quadrupedal when feeding from the ground. It was probably about 26 feet long from snout to tail. The skull measures about 30 inches long. It had a wide mouth and a unique tall arch on top of the snout, from which the dinosaur derives its name.

The forelimbs were roughly half the length of the hindlimbs. The carpals (wrist joints) were thick and blocky, and the three middle fingers on the hand were wide with hoof-like bones. The forelimbs were capable of supporting weight, which supports the idea of it being quadrupedal at least while feeding. The two outside fingers were modified for different uses. The thumb spike may have been used for breaking shells of seeds or fruit. The other was somewhat opposable to the rest of the hand and may have been used for grasping food.

Altirhinus had a large gap between its beak on the front of the mouth and the main chewing cavity in the side of the mouth. This would allow the dinosaur to crop food with its beak while chewing its teeth. Many herbivorous mammals show similar adaptation and can crop with their incisors without disturbing their chewing molars.

The characteristic arched snout of Altirhinus was formed primarily by the nasal bones, and a similar structure is seen on the snout of the Australian Muttaburrasaurus. Many different functions have been proposed for the nasal arch. It may have housed tissues to cool the blood, conserve water, or enhance the sense of smell. Alternatively, it may have facilitated communication through vocalization or visual display. As only two skulls have been located, it is entirely possible that the arched snout is only found in one gender, in which case it may have been used for sexual display, like in modern-day elephant seals.

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Altirhinus