The Ischigualasto Formation contains Late Triassic (Carnian) deposits (231.4 -225.9 million years before the present), with some of the oldest known dinosaur remains, which are the world's foremost with regards to quality, number and importance.
This allows for the study of the transition between dinosaurs and ancient mammals; research is ongoing.

In the Carnian this area was a volcanically active floodplain dominated by rivers and had a strongly seasonal rainfall.
Petrified tree trunks of Protojuniperoxylon ischigualastianus more than 40 m (130 ft) tall attest to a rich vegetation at that time.
Fossil ferns and horsetails have also been found.

Rhynchosaurs and cynodonts (especially rhynchosaur Hyperodapedon and cynodont Exaeretodon) are by far the predominant findings among the tetrapod fossils in the park.
A study from 1993 found dinosaur specimens to comprise only 6% of the total tetrapod sample; subsequent discoveries increased this number to approximately 11% of all findings.
Carnivorous dinosaurs are the most common terrestrial carnivores of the Ischigualasto Formation, with herrerasaurids comprising 72% of all recovered terrestrial carnivores.
Dinosaurs of Ischigualasto Formation include early samples of the two major lineages of dinosaurs (ornithischians and saurischians).
The carnivorous archosaur Herrerasaurus is the most numerous of these dinosaur fossils.
Another important putative dinosaur with primitive characteristics is Eoraptor lunensis, found in Ischigualasto in the early 1990s.
The Ischigualasto Formation contains Late Triassic (Carnian) deposits (231.4 -225.9 million years before the present), with some of the oldest known dinosaur remains, which are the world's foremost with regards to quality, number and importance. This allows for the study of the transition between dinosaurs and ancient mammals; research is ongoing.
In the Carnian this area was a volcanically active floodplain dominated by rivers and had a strongly seasonal rainfall. Petrified tree trunks of Protojuniperoxylon ischigualastianus more than 40 m (130 ft) tall attest to a rich vegetation at that time. Fossil ferns and horsetails have also been found.
Rhynchosaurs and cynodonts (especially rhynchosaur Hyperodapedon and cynodont Exaeretodon) are by far the predominant findings among the tetrapod fossils in the park. A study from 1993 found dinosaur specimens to comprise only 6% of the total tetrapod sample; subsequent discoveries increased this number to approximately 11% of all findings. Carnivorous dinosaurs are the most common terrestrial carnivores of the Ischigualasto Formation, with herrerasaurids comprising 72% of all recovered terrestrial carnivores. Dinosaurs of Ischigualasto Formation include early samples of the two major lineages of dinosaurs (ornithischians and saurischians). The carnivorous archosaur Herrerasaurus is the most numerous of these dinosaur fossils. Another important putative dinosaur with primitive characteristics is Eoraptor lunensis, found in Ischigualasto in the early 1990s.
Ischigualasto Provincial Park