Tetanurae

Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") are a clade which includes most theropod dinosaurs, including birds. Tetanurans first appear in the Jurassic. It is a large group of theropod dinosaurs. Jacques Gauthier used the term when he first applied cladistics to vertebrate paleontology.
The term refers to the stiff tail which was held above the ground as a counterweight when the animal walked or ran.
Tetanurae are defined as all theropods more closely related to modern birds than to "Ceratosaurus". Gauthier considered it to consist of Carnosauria and Coelurosauria. Modern birds are the only living representatives of the clade Tetanurae.