Supercontinent Pangea

Introduction

Although the Earth may seem to have a solid outsideits exterior layer (the crust) is actually broken into a number of tectonic plateseach moving very slowly in response to movement of the slowly flowing mantle beneath. Earth’s continents and oceans are shaped by the movements of these tectonic plates. Sometimes they collide. When this happenstheir edges are thrust up into mountains if neither plate is denser than the otherwhile if the plates have different densitiesthe denser plate sinks under the less dense plate and meltscausing magma to rise up and form volcanos. Sometimes two plates separateand volcanos occur at the gaplike at the mid-ocean ridges beneath the sea. Finallyin other cases plates slide next to each other; if the plates catchearthquakes occur.

Before the Triassic beganapproximately 252 million years agothe plates had moved in such a way that all of the major landmasses had collided with each otherforming a supercontinent which is called Pangea. This had taken hundreds of millions of years as one continent after another was collected in the whole. You can get an idea of the shape of the core of Pangea by looking at the east coasts of North and South America and the west coast of Africa: when these continents were part of Pangeathese coasts fit together approximately. Antarctica was connected to southeast Africaand southern Australia to Antarcticawith India (a separate continental block from the rest of Asia) and Madagascar between east AfricaAntarcticaand west Australia. Southwest Europe was wedged between northeast North America and northwest Africawith much of the rest of Eurasia extending off to the northeast.

Rugged mountain ranges similar to the Himalayas formed along the boundaries; one of these is the Appalachiansnow much lower thanks to 250 million years of erosion. The combination of huge internal mountain ranges and vast unbroken expanses of land and sea led to much different climates compared to today. There were great interior deserts and more extreme temperatures from the poles to the equator. Animals could walk from one end of Pangea to the otherbut much of it would have been harsh to live in. The formation of Pangea is also thought to have contributed to marine extinctions during the preceding Permian Period by the reduction of shallow marine shelf environmentswhere much marine diversity is concentrated.

Supercontinents don’t last forever. While it is not understood completely why they break upwe can guess that it has to do with the uneven distribution of different kinds of crust. Pangea began to break up toward the end of the Triassicfirst along the boundary between North America and Africa. The original continental boundary wasn’t exactly reproduced; insteadNorth America gained a chunk of land that today includes Florida and nearby parts of the southeastern United States. As the two continents began to move in different directionslong narrow rift valleys formed along the seam. Today something similar is happening in east Africaand is responsible for the Great Lakes of this region. Like the African Great Lakesthe eastern margin of North America in the Late Triassic featured a number of longlinear lakes and basinsfrom Nova Scotia to South Carolina. At the very end of the Triassicapproximately 201 million years agohuge amounts of lava erupted over a short time along the boundary from southwest Europe to northeast South America as what is now the North Atlantic began to open. The breakup of Pangea was in full swingbut would not be complete until much later.

Rocks deposited in the rift basins in eastern North America are classified in the Newark Supergroup. They have produced footprintsbonesand other fossils of the organisms that lived here during the transition from the Triassic to the Jurassicincluding plantsfreshwater invertebratescrocodile relativesand early dinosaurs and their cousins. Because some of these rocks are found in New England and the Mid-Atlantic statestheir fossils were among the first studied in North America. Edward Hitchcock pioneered the study of the tracks in the mid-19th centuryand both of the leading figures of the “Bone Wars”Edward Drinker Cope and Othniel Charles Marshdescribed fossils from these rockspractically their back yards. Dinosaur State Park and Arboretum (a National Natural Landmark) in Connecticut preserves tracks from one of these rift basins. To the north in MassachusettsSpringfield Armory (now Springfield Armory National Historic Site) was the site of one of the best early dinosaur discoveries in the worlda partial skeleton of a sauropod cousin now named Anchisaurus. It was discovered during blasting for construction in 1855.

Related Links

• NPS—Fossils and Paleontology

• NPS—National Natural Landmarks

• National Fossil Day Partnership

• NPS—Geology

• NPS—Geologic Time Scale

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 DevelopmentJim Wood (GRD).

References

• TweetJ.S. and V.L. Santucci. 2018. An Inventory of Non-Avian Dinosaurs from National Park Service Areas. in LucasS.G. and SullivanR.M.(eds.)Fossil Record 6. New Mexico Museum of Natural History and Science Bulletin 79: 703-730. https://irma.nps.gov/DataStore/Reference/Profile/2257153

• SantucciV.L.A. MarshW. ParkerD. Chureand D. Corrick2018. “Age of Reptiles”: Uncovering the Mesozoic Fossil Record in three Intermountain national parks. IMR Crossroads. Spring 2018p. 4-11. https://irma.nps.gov/DataStore/Reference/Profile/2253529