Tochisaurus

*Tochisaurus nemegtensis*

Tochisaurus ("ostrich") is an extinct genus represented by a single species of troodontid theropod dinosaur, which lived at the end of the Cretaceous period, in the Maastrichtian era, in what is today Asia. Tochisaurus is a troodontid known only from metatarsals II, III, IV, which is estimated to have measured around 3 meters long and 0.8 meters high, weighing close to 50 kilograms. It is characterized by the inclined proximal surface of the metatarsals and a strong reduction of metatarsal II which suggests that the metatarsal claw was not particularly large.

## Description

The holotype was found in 1948 by a Soviet-Mongol expedition in the Nemegt Formation, in the Gobi Desert near Omnogov, Mongolia. In 1987 this finding was reported by Sergei Kurzanov who described it as an indeterminate theropod and Halszka Osmólska in the same year identified it as a troodontid. In 1987 Osmolska suggested that it was a specimen from Borogovia.

Later Osmólska understood that it would be a new species for science. She and Kuraznov in 1991 formally named it Tochisaurus nemegtensis . The name of the genus is derived from the Mongolian term toch' , "ostrich", in reference to the fact that the foot, like that of that bird, was functionally didactyl, that is, only two toes supported the weight of the animal. The name of the species, for its part, refers to the Nemegt. The authors noted the greater reduction of the distal end of the metatarsal II, and it differs from Saurornithoides junior by the inclination of the proximal surface of the metatarsals and that they are narrower, however not it was compared to S. mongolensis.

The holotype fossil is specimen PIN 551-224 , which was found in a layer of the Nemegt Formation, which dates back to the early Maastrichtian, about 69 million years old. It consists only of a left metatarsal, the first known for an Asian troodontid. The first metatarsal is missing. The top of the fossil shows some damage which was originally inexpertly restored.

Tochisaurus was a bipedal dinosaur. The metatarsus had a length of 242 millimeters, indicating that it was a relatively large troodontid. The second metatarsal, 222 millimeters long, is greatly reduced and narrow. The surface of the top of the metatarsal has a forward and downward slope.

Based on these partial fossils, it is thought that Tochisaurus was a member of the family Troodontidae.

## JPInstitute.com Description

Scientists currently believe that Tochisaurus was a swift, smart hunter from Asia. This is only a guess, however, as only part of the foot has been found! Three parts of the upper foot bone were found perfectly preserved and based on this, scientists think that they have a pretty good idea of how this and other members of its family would have looked. It belongs to the same group of dinosaurs that included Troodon, and it probably looked very similar to that North American dinosaur. This is another example of how dinosaurs of the same basic family spread through different parts of the prehistoric world.

Tochisaurus is known from its well-preserved metatarsus, which measures about 10 inches (25 cm) long. It is believed to be closely related to Troodon, but distinct enough to warrant a separate genus.

## Links

https://web.archive.org/web/20030324205533/http://www.jpinstitute.com/dinopedia/dinocards/dc\_tochi.html
https://web.archive.org/web/20080720024743/http://kids.yahoo.com/dinosaurs/175--Tochisaurus