Triassic Dinosaurs

painting of dinosaurs in river bed (copyrights—temporary use do not copy or distribute)
Triassic life and landscape visitor center mural. Dinosaur State Park, Connecticut. Dinosaur State Park is a designated National Natural Landmark.

Friends of Dinosaur Park and Arboretum mural by William Sillin.


Dinosaurs evolved in a world that had one supercontinent, Pangaea, surrounded by one ocean, Panthalassa. The Atlantic Ocean did not exist; instead, Africa was joined to North America along much of what would be today’s Atlantic coast, forming the arid and inhospitable interior of the supercontinent. The Appalachian Mountains were much taller and more rugged. To the west, today’s Pacific coast did not exist yet, either. Instead, the land that would become the Pacific coast states was either not yet attached to North America or was under water. The Colorado Plateau and the Rocky Mountains did not exist yet, and in their place were vast lowlands near sea level. Volcanoes fringed the western margin of the continent.

The ancestors of dinosaurs were one of several groups of reptiles that benefited from the Permian–to–Triassic extinction approximately 252 million years ago. These ancestors were lightly built two-legged animals, around the size of a crow. Our best evidence of the earliest dinosaur ancestors comes from South America. True dinosaurs evolved by approximately 233 million years ago, early in the Late Triassic, and spread across the connected continents.

The record of dinosaurs in North America begins during the Late Triassic, approximately 225 million years ago. These early dinosaurs were mostly small, lightly built two-legged carnivores, including animals such as Coelophysis and its close relatives. Larger carnivorous and herbivorous dinosaurs are represented by tracks. Dinosaurs were not a major part of Late Triassic faunas, which include a wide variety of amphibians, mammal cousins, and reptiles, most famously the crocodile-like phytosaurs and the armored aetosaurs. Almost all of these other groups would go extinct at the end of the Triassic, 201 million years ago, in a major extinction event generally thought to have been caused by massive volcanic activity. Mammal cousins, the ancestors of today’s amphibians and reptiles, pterosaurs, marine reptiles, and dinosaurs persisted.

Life and Death in the Triassic

Meet the Dinosaurs

Triassic Dinosaurs in Parks

Dinosaurs from Triassic rocks (252 to 201 Ma) in the NPS are best known from Petrified Forest National Park (Arizona), which has most of the few Triassic dinosaur body fossils from the NPS. The park’s Triassic dinosaurs were “supporting players” in an ecosystem dominated by crocodile-like phytosaurs, armored aetosaurs, and giant amphibians. Other Triassic NPS dinosaurs are known almost entirely from tracks, mostly representing small three-toed predators. At Gettysburg National Military Park (Pennsylvania) and Valley Forge National Historical Park (Pennsylvania), visitors may see Triassic dinosaur tracks in locally quarried building stone.

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National Natural Landmarks—Triassic Dinosaurs

  • Ghost Ranch National Natural Landmark, New Mexico

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    Site Index and Credits

    Age of Dinosaurs (2021)

    Text by Justin Tweet (AGI). Contributors: Vincent Santucci (GRD), Adam Marsh (PEFO), ReBecca Hunt-Foster (DINO), Don Corrick (BIBE). Project Lead / Web Development, Jim Wood (GRD).


    • Tweet, J.S. and V.L. Santucci. 2018. An Inventory of Non-Avian Dinosaurs from National Park Service Areas. in Lucas, S.G. and Sullivan, R.M., (eds.), Fossil Record 6. New Mexico Museum of Natural History and Science Bulletin 79: 703-730.

    • Santucci, V.L., A. Marsh, W. Parker, D. Chure, and D. Corrick, 2018. “Age of Reptiles”: Uncovering the Mesozoic Fossil Record in three Intermountain national parks. IMR Crossroads. Spring 2018, p. 4-11.

    Last updated: May 30, 2023


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