MEANING: Narrow claw lizard
PERIOD: Late Cretaceous
CONTINENT: North America
Stenonychosaurus is a troodontid dinosaur known for having one of the largest brains, relative to body mass, of any dinosaur. Its eyes were also very large, suggesting possibility of a nocturnal lifestyle. Stenonychosaurus grew to about 2.5 m in length and had long legs for running, with large retractable claws on the second toe, similar to dromaeosaurs. Studies of troodontid nests show that multiple females would lay eggs in a single nest, which was then brooded by the male. Due to scant remains, mostly relying on their tiny teeth, classification of the troodontid family has been convoluted, and it is likely that Stenonychosaurus is the same genus as Troodon.
Stenonychosaurus is from the Cretaceous. The Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct flora and fauna, while dinosaurs continued to dominate on land. The world was ice free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras.
Stenonychosaurus is a troodontid. Troodontidae is a family of theropod dinosaurs which are closely related to birds. Many genera are known only from teeth, and this has led to much debate and reclassification over the course of the history of paleontology. The oldest definitive troodontid is known from the Late Jurassic of Wyoming. Over the Cretaceous, they radiated throughout western North America, Asia, and Europe, suggesting a mostly Laurasian distribution.
Troodontids are small, bird-like, gracile maniraptorans. They have unique skull features, such as large numbers of closely spaced teeth in the lower jaw. They are also equipped with sickle-claws and raptorial hands, similar to the closely related dromaeosaurs. Troodontids also had unusually large brains and eyes, suggesting that they were behaviourally advanced and had keen senses.