Troodon (Stenonychosaurus)!

Troodon (or Troödon in older sources) is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period (75-65 mya). Discovered in 1855, it was among the first dinosaurs found in North America.

Its name (pronounced /ˈtroʊ.ɵdɒn/ TROE-o-don) is Greek for "wounding tooth", referring to the dinosaur's teeth, which are different from those of most other theropods. The teeth bear prominent, apically oriented serrations. These "wounding" serrations, however, are morphometrically more similar to those of herbivorous reptiles, and suggest a possibly omnivorous diet.

 Troodon was a small dinosaur, around 2 metres (6.6 ft) in length, 1 metre (3.3 ft) tall, and weighed about 27 to 45 kilograms (60 to 99 lb). It had very long, slender limbs, suggesting that the animal was able to move quickly. It had long 'arms' that folded against the wall of the thorax like a bird's. It had large, retractable sickle-shaped claws on its second toes, which were raised off the ground when running.

 

The first specimen of Troodon that was not a tooth, then referred to its own genus (Stenonychosaurus), was named by Sternberg in 1932, based on a foot, fragments of a hand, and some caudal vertebrae from Alberta. A remarkable feature of these remains was the enlarged claw on the second toe, which is now recognized as characteristic of Deinonychosauria. Sternberg initially classified Stenonychosaurus as a member of the family Coeluridae. Later, Sternberg (1951) speculated that since Stenonychosaurus had a "very peculiar pes" and Troodon "equally unusual teeth", they may be closely related. Unfortunately, no comparable specimens were available at that time to test the idea.

Stenonychosaurus has been credited with being the most intelligent dinosaur. Compared with most others, it had a relatively large brain, although the excess brain volume was probably not concerned with reasoning and other activities that could be called "intelligence."