Herrerasaurus

Herrerasaurus was one of the earliest dinosaurs. All known fossils of this carnivore have been discovered in Upper Triassic strata dated to 231.4 million years ago (mya) in northwestern Argentina.
It is a member of the Herrerasauridae, a family of similar genera that were among the earliest dinosaurs.
Description.
"Herrerasaurus" was a lightly built bipedal carnivore with a long tail and a relatively small head. Its length is estimated at 3 to 6 meters (10 to 20 ft), and its hip height at more than 1.1 meters (3.3 ft). It may have weighed around 210–350 kilograms (463–772 lb).
In a large specimen the skull measured 56 centimeters (1.8 ft) in length. Smaller specimens had skulls about 30 centimeters (1 ft) long.
The tail, partially stiffened by overlapping vertebral projections, balanced the body and was also an adaptation for speed.
Palaeoenvironment.
The paleoenvironment of the Ischigualasto Formation (where it was found) was a volcanically active floodplain covered by forests with seasonal rainfall. The climate was moist and warm, with seasonal variations. The vegetation was ferns, horsetails, and giant conifers. These plants formed lowland forests along the banks of rivers. "Herrerasaurus" was the most common of the carnivores of the Ischigualasto Formation.
"Herrerasaurus" lived in these jungles alongside a smaller dinosaur, the one metre long "Eoraptor". "Saurosuchus", a huge quadrupedal Archosaur was the biggest land predator at the time. There were also a number of therapsid and reptilian herbivores. The dinosaurs had not yet taken control of the land environments as they did later.