The Handy Dinosaur Answer Book. Patricia Barnes-Svarney
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plates?
Not everyone agrees on why the continental plates move across Earth—but there are some theories. In general, the continental plates are made of light material that “floats” on the heavier, molten material of Earth’s interior (called the mantle). As the upper part of the mantle circulates and moves, it slowly “carries” the plates around the planet.
What are the consequences of continental plate movements?
As the term implies, the movement of the continental plates changes the positions of the continents. Along the continental boundaries, volcanoes and mountains form as the plates interact with each other. Some continents slowly crash into one another, forming huge mountain chains, such as the Himalayas in Asia (from the collision of the Indian and Asian plates). Other plates slide under one another in areas called subduction zones. The Andes Mountains are the result of a subduction zone between the Nazca and South American plates. Still other plates slip right by one another, such as the Pacific and North American plates. In this case, the slipping of the plates creates the San Andreas fault in California.
But there are other consequences of continental plate movement. In particular, this process also opens and closes the seas, changing ocean currents—and thus climates—around the world. In addition, volcanoes can form as plates sink under each other, and earthquakes can occur.
What did our planet look like at the start of the Triassic period?
Continental plate movements have a variety of effects upon the planet, ranging from shifts in temperature to devastating earthquakes. Plate tectonics affect us today, just as they affected the dinosaurs millennia ago (iStock).
Similar to today, most of the planet during the Triassic period was covered by ocean, but the distribution of the landmasses was not the same. Scientists believe there was essentially one large expanse of water called the Panthalassa Ocean. It surrounded the one very large landmass, or supercontinent, called Pangea, meaning “all Earth.” This giant landmass straddled the planet’s equator roughly in the form of a “C”; the smaller body of water enclosed by the “C” on the east was known as the Tethys Sea (or Tethys Ocean). Only a few scattered bits of continental crust were not attached to Pangea, and lay to the east of the larger continent. They included pieces of what we now call Manchuria (northern China), eastern China, Indochina, and bits of central Asia. In addition, the sea level was low, and there was no ice at the polar regions.
What led to the original formation of the supercontinent Pangea?
The same process that would eventually break apart Pangea led to its formation—the continents seemingly moving around the planet like icebergs on an ocean. There were two large landmasses on Earth during the Paleozoic era—Laurasia (North America and Eurasia) to the north of the equator, and Gondwanaland (or Gondwana, including South America, Africa, India, Antarctica, and Australia) to the south of the equator. These two continents slowly collided during the Late Paleozoic era, forming the supercontinent of Pangea. By the beginning of the Mesozoic era, Pangea was still the only true continent on the planet.
How did the supercontinent Pangea change during the Triassic period?
In the Early Triassic period, Pangea gradually began to break apart into two major continents again, the result of a seafloor-spreading rift. (This rift was similar to today’s Mid-Ocean Ridge in the Atlantic Ocean, a volcanic seam that continues to spread, and along which the volcanic island of Iceland was born.) The Triassic rift extended westward from the Tethys Sea across what is today the Mediterranean Sea. The action of this rift separated northern Laurasia from southern Gondwanaland, which would eventually lead to the opening of the proto-Atlantic (or early Atlantic) Ocean. As North Africa split from southern Europe, there was a gradual rise in sea level that flooded south and central Europe.
Towards the Middle and Late Triassic periods, the spreading rift between North Africa and Europe grew westward, and it began to separate North Africa from the eastern part of North America. The resulting rift valley was the first true stage in the formation of the proto-Atlantic Ocean.
How did this continental configuration affect the dinosaurs?
During the Early Triassic period, the supercontinent Pangea allowed the precursors of dinosaurs to roam all over the huge landmass. As the supercontinent slowly split in two, it eventually cut off certain emerging dinosaur species from other species. The movements also caused certain ocean areas to widen and led to the inundation of parts of the landmasses, thus changing shorelines. This changed the types of vegetation and animal life in certain regions.
As Pangea began to break up, it formed two smaller supercontinents that scientists have named Laurasia and Gondwanaland (based on a map from the U.S. Geological Survey).
It is difficult to mention all the minute changes that occurred over such a broad expanse of time. But there are generalities: for example, as the Atlantic Ocean opened, lakes that eventually became the ocean grew larger and smaller—and even divided. These changes were often accompanied by an absence or abundance of sea life. Shorelines often grew rich in plant and animal life. We know that some dinosaurs came down to eat and drink around these changing lakes, as their tracks have been discovered in sediment that once lay along the shorelines.
Where are Triassic period rocks found?
Layers of Triassic period rocks are found in many countries around the world. They occur in certain localities in eastern and western North America, South America, the British Isles, western Europe, Asia, Africa, and Australia. The thickest Triassic period rock layer so far discovered lies in the Alps, measuring about 25,000 feet (7,500 meters) thick.
What is the Newark Supergroup and why is it significant?
The Newark Supergroup is a layer of Triassic period rocks located in the eastern United States; it is famous for its rocks and fossils from this period. The rock layers represent the remnants of several thousands of feet of sedimentary and volcanic rocks deposited in a chain of basins over a span of 45 million years. This layer is found in many locations, including New Jersey, Virginia, and North Carolina. The sedimentary strata contains a good cross-section of fossils from the Late Triassic period, including insects, fish, turtles, archosaurian reptiles (including dinosaurs, lizards, and snakes), lissamphibians (frogs, salamanders, and caecilians), and numerous plant fossils. Paleontologists hope to find additional vertebrate fossils in the Newark Supergroup layers that will shed more light on the evolutionary stages that led to groups of many organisms—especially the dinosaurs—during the Triassic period.
One of the richest fossil deposits from the Triassic period, the Newark Supergroup is located in the eastern United States (iStock).
The Newark Supergroup—indeed most of the area of the rift valley called the Atlantic Rifting Zone—is famous for reptile footprints, with tens of thousands of extremely well-preserved tracks from the Triassic and Jurassic periods. The tracks were first recognized in 1836 by U.S. paleontologist, the reverend Edward Hitchcock, a professor of natural theology and geology at Amherst College. He also described the Connecticut River Valley dinosaur footprints. These tracks are important because they show evidence of the evolution and eventual dominance of the dinosaurs.
What is the Ischigualasto formation and why is it important?
The Triassic rocks of the Ischigualasto formation of Argentina are thought to be some of the richest fossil deposits,