The Chinle Group - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 133

D ESCRIPTIONS OF THE C HINLE
G ROUP BIOTA
Dinosaurs
The theropod dinosaur, Coelophysis ( 134,
135 ), is known mainly from the mass grave
at Ghost Ranch Quarry in New Mexico
where hundreds of skeletons were
preserved. It was a small, delicate dinosaur
characterized by a long neck and
elongated skull balanced by a long,
slender tail. The hind limbs, with three-
toed feet, were like those of a long-legged
ground bird, but the forelimbs were small
with tiny, three-fingered hands. This
carnivore was both an active hunter and a
scavenger, but was only 3 m (10 ft) in
length and just 1 m (3 ft) tall. Because of
its hollow bones (the name means 'hollow

form') it had a lightweight, agile body of
only about 40 kg (100 lb). It is one of the
earliest known dinosaurs. Other dinosaurs
are not common - the ornithischian,
Revueltosaurus , has been recorded from
isolated teeth by Padian (1990) from the
upper unit of the Petrified Forest
Formation in Arizona.

Mammal-like reptiles
The dicynodont mammal-like reptile,
Placerias ( 136 ), is known from over 40
individuals preserved at Placerias Quarry
near St Johns in Arizona, but from few
other localities worldwide. These heavily-
built, ungainly-looking herbivores fed in
large, slow-moving herds and defended
themselves with two long tusks, which were

134

134 The theropod dinosaur
CoelophysisYPM. Length
3m10 ft.

135

135 Reconstruction of
Coelophysis.