Coelophysis

MEANING: Hollow form

PERIOD: Late Triassic

CONTINENT: North America

Coelophysis is a basal theropod, and one of the earliest known dinosaurs. It was a small slender bipedal carnivore that measured up to 3 m in length, and weighed around 20 kg. Coelophysis had a narrow head with an elongated snout, and finely serrated teeth, which it likely used to feed on smaller lizard-like animals.

Coelophysis is from the Late Triassic. The Triassic is the first geologic period of the Mesozoic, spanning from the end of the Permian Period 252 million years ago to the beginning of the Jurassic 201 million years ago. Both the start and end of the Triassic were marked by major extinction events. In the aftermath of the devastating Permian-Triassic extinction, life gradually rebounded, giving rise to new groups that would shape the Mesozoic Era. The global climate during the Triassic was mostly hot and dry, with vast deserts dominating the interior of the supercontinent Pangea. Over time, as Pangea began to rift apart, the climate slowly became more humid, creating new environments and opportunities for ecological diversification.

For much of the Triassic, dinosaurs were not yet the dominant terrestrial animals. Instead, the land was populated by a variety of other reptiles, including sprawling archosaurs. Early synapsids, the lineage that would eventually lead to mammals, were also still present but declining. Vegetation was dominated by drought-tolerant plants such as seed ferns, cycads, ginkgoes, and early conifers. These hardy plants formed the base of recovering ecosystems during this volatile time.

It wasn't until the Late Triassic, around 230 million years ago, that the first true dinosaurs appeared. Early forms were small, bipedal, and lightly built, likely preying on insects and small vertebrates. While they remained minor players compared to other reptilian groups, their agility, upright stance, and efficient breathing gave them advantages that would prove crucial in the long run. As the Triassic drew to a close, another mass extinction event reshaped life on Earth once again—wiping out many of the dominant reptile groups and clearing the way for dinosaurs to rise to prominence in the Jurassic.

Coelophysis is a coelophysoid. Coelophysoidea is a group of early, basal theropods that emerged during the Late Triassic and persisted into the Early Jurassic. These were among the first dinosaurs to take on the classic theropod form - lightweight, bipedal, and built for speed. Coelophysoids were generally slender and agile, with long tails for balance, narrow skulls lined with sharp teeth, and strong hind limbs ideal for running. They weren’t the largest predators of their time, but their speed and coordination may have made them efficient hunters, preying on small vertebrates and possibly scavenging when the opportunity arose.

Fossils of Coelophysis are especially abundant, with large bonebeds found in what is now the southwestern United States, suggesting they may have lived and traveled in groups. Though small compared to later theropods - usually only a few meters long - coelophysoids laid much of the groundwork for the evolutionary path of theropod dinosaurs. Their lightweight build, hollow bones, and fast locomotion were traits that would be refined over millions of years.