Which early dinosaur is known from a mass burial in New Mexico?

The early dinosaur known from a mass burial in New Mexico is Coelophysis.

Coelophysis was a lightly built, bipedal theropod from the Late Triassic. Its most famous fossils come from the Ghost Ranch area of northern New Mexico, where paleontologists found hundreds of skeletons concentrated in a single bonebed. The discovery was made during American Museum of Natural History fieldwork in 1947, led by Edwin H. Colbert.

The Ghost Ranch quarry is part of the Chinle Formation and dates to roughly 212 million years ago. The dense accumulation was probably created when a flash flood swept up and rapidly buried many animals, although the exact circumstances of the bonebed remain a subject of scientific study. The site provided an unusually detailed look at one early dinosaur population.

Coelophysis was a slender predator with hollow bones, a long tail, and sharp teeth. It is often confused with other early theropods such as Dilophosaurus, but Dilophosaurus lived later and is best known from Arizona. Herrerasaurus was also an early dinosaur, but it is not the animal associated with the famous New Mexico mass burial.