Team explains how dinosaurs rose to prominence

Mar 22, 2010
Massive lava flow (top brown layer) sits atop end-Triassic (white) and Triassic (red) layers at a site in Five Islands Provincial Park, Nova Scotia. Credit: Jessica H. Whiteside/Brown University

A shade more than 200 million years ago, the Earth looked far different than it does today. Most land on the planet was consolidated into one continent called Pangea. There was no Atlantic Ocean, and the rulers of the animal world were crurotarsans - creatures closely related to modern crocodiles.

Yet the Earth stood on the cusp of an epic shift in climate, and the reign of the dinosaurs was about to begin. Now, an international scientific team led by Brown University paleobiologist Jessica Whiteside has explained what led to the dinosaurs' rise as the ended.

In a paper published in the , the scientists constructed a climate record marking the Triassic-Jurassic boundary by combining of plant and animal extinctions with the carbon signature found in the wax of ancient leaves and wood found in lake sediments intermixed with basalts, marking the volcanic activity.

With those evidentiary threads, the researchers found strong support that massive, widespread volcanic eruptions led to a spike in atmospheric and other greenhouse gases that wiped out half of plant species and marked the end of the Triassic, one of the five great mass extinctions of Earth history.

The team also established through the fossil record that the abrupt rise in atmospheric gases decimated crurotarsans, which had competed vigorously with the earliest dinosaurs during the Triassic. Thanks to the climatic catastrophe, those early, small dinosaurs were freed from their main competitors to become the dominant force in the animal world.

"The big thing is many people have heard why dinosaurs went extinct," said Whiteside, assistant professor of geological sciences, "but the question why they came to be is much more exciting."

What scientists know is that more than 200 million years ago, the supercontinent Pangea broke up when the North American and the African plates began to drift apart. As the two plates parted, creating the basin that would become the Atlantic Ocean, fissures cleaved the area, triggering massive outflows of lava covering more than 9 million square kilometers (3.5 million square miles), an area roughly equal to the continental United States. Scientists call this area the Central Atlantic Magmatic Province (CAMP). The volcanic eruptions lasted about 600,000 years, a length of time that Whiteside estimated in a 2007 paper in Palaeogeography, Palaeoclimatology, Palaeoecology.

The researchers zeroed in on rift basins preserving the CAMP to figure out precisely what happened to the climate and to plants and animals. The team, including researchers from Academia Sinica in Taiwan, Columbia University, and the Woods Hole Oceanographic Institution, analyzed fossils and carbon signatures from two ancient basins in the northeast United States — the Newark and Hartford basins — as well as a basin in England. At these sites, the researchers found evidence where fossilized sediments from lakes that dotted Pangea before the plates' separation were preserved between lava flows. The team dated the oldest flows to 201.4 million years ago, providing an upper limit to when volcanism began.

Those fossils told a clear tale: For plants, pollen counts combined with the carbon record (the ratio of C12 and C13, two carbon isotopes) showed half the flora species in the Triassic perished in the volcanism that marked the end of the period. It also showed a spike in fern spores around the time of the first lava flows, which makes sense as ferns are among the first plant species to return in an environment scarred by volcanism.

Brown University paleobiologist Jessica Whiteside led a scientific team that has explained what led to the dinosaurs’ rise as the Triassic Period ended. Fossil and carbon evidence show that volcanic eruptions and a spike in atmospheric carbon dioxide wiped out half of plant species and early dinosaurs' primary competitors. Credit: Paul Olsen/Columbia University

For animals, the scientists linked footprints previously found in rocks in the Hartford and Newark basins to establish that crurotarsans perished in the mass volcanism that marked the end of the Triassic. After the lava flows, the "fossil record for crurotarsans is nearly completely gone," Whiteside said. Freed from their main competitor, early theropods — a category including all meat-eating dinosaurs from velociraptors to Tyrannosaurus rex — became dominant. Evidence for the rise was documented in a paper published in 2002 by Paul Olsen (corresponding author on the PNAS paper) that shows theropod footprints after the mass extinction at the end of the Triassic had become much larger, corresponding to larger body sizes.

Why did the early dinosaurs survive the volcanism that extinguished the Triassic crurotarsans? "They had the blind luck of being unwittingly adapted to get through that climate catastrophe," Whiteside said. "How they did is quite difficult to explain."

While previous research on end-Triassic mass extinctions has been done in other regions, such as Greenland, this paper marked the first time that scientists had gathered and calibrated evidence from the CAMP, said Olsen, a paleontologist who has studied mass extinction events for three decades at Columbia.

"There are dozens of papers claiming to show the connection between carbon isotopes excursions in the CAMP," Olsen said, "but this is the only study that has ever shown isotope excursions from the same place that the were present."

"It's not that we're the first people to say there's a link" (between volcanism and end-Triassic mass extinction), Whiteside added, "but we're the first people to document it."

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JayK
1 / 5 (3) Mar 22, 2010
When one of your parents are nephilim, I guess you deserve to be on top.
moj85
not rated yet Mar 22, 2010
This doesn't explain how dinosaurs rose to prominence. It explains why the previous top predators - crurotarsus - went nearly extinct. Why were the dinosaurs adapted better? How did the climate change?
Skeptic_Heretic
not rated yet Mar 22, 2010
When one of your parents are nephilim, I guess you deserve to be on top.

I laughed.
Sonhouse
not rated yet Mar 22, 2010
Like they said, it may have been simple luck: They could have been concentrated in areas not as hard hit by the volcanism while their competitors were closer to ground zero.
jimbo92107
5 / 5 (1) Mar 23, 2010
Or maybe dinosaurs had more efficient lungs, like birds. If volcanism pumped up the CO2 percentage, then lungs like a bird would have kept dinosaurs active enough to out-compete crurotarsans.
Parsec
not rated yet Mar 23, 2010
This doesn't explain how dinosaurs rose to prominence. It explains why the previous top predators - crurotarsus - went nearly extinct. Why were the dinosaurs adapted better? How did the climate change?


Temperature spiked from CO2 rises. We are talking about very large temperature rises. Volcanism at that level puts out out huge amounts of pollution.

My guess is that dinos had better temp regulating mechanisms, or their lungs were able to cope with more respiratory distress, or both.
squiffy
not rated yet Mar 23, 2010
If the volcanism of the Siberian traps continue for 600,000 years as in the article, the emissions of dust an particles would have likely blotted out most of the sunlight. Animal as well as plant life, both of which are dependent on sunlight, would have ceased causing the "Great Dying". Heat input by that volcanism would be offset by global cooling due to the lack of sunlight. All forms of life would have had a hard time getting re-established.
dferrantino
not rated yet Mar 23, 2010
Or maybe dinosaurs had more efficient lungs, like birds. If volcanism pumped up the CO2 percentage, then lungs like a bird would have kept dinosaurs active enough to out-compete crurotarsans.

Makes sense considering their future lineage...

If the volcanism of the Siberian traps continue for 600,000 years as in the article, the emissions of dust an particles would have likely blotted out most of the sunlight. Animal as well as plant life, both of which are dependent on sunlight, would have ceased causing the "Great Dying". Heat input by that volcanism would be offset by global cooling due to the lack of sunlight. All forms of life would have had a hard time getting re-established.

Just because there's a lot of volcanic activity doesn't mean there's going to be widespread ash. Fissure eruptions tend to produce comparatively little ash, and from the article, that's what this situation was.
Megapixel
1 / 5 (5) Mar 27, 2010
The Gravity Theory of Mass Extinction would explain this extinction event differently. The formation of Pangea lowered surface gravity due to core shifting. At the T-J boundary, the inital breakup of Pangea created a pulse of higher surface gravity. This would have been detrimental to sprawling-legged crurotarsans, which it was, allowing the straight-legged dinosaurs to flourish.