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Geology | Fossil record's timely warning: Mammals slow to bounce back from disaster

The Columbus Dispatch logo The Columbus Dispatch 1/5/2020 By Dale Gnidovec, For The Columbus Dispatch, The Columbus Dispatch
a close up of a rock: Fern fossil collected from Corral Bluffs, Colo. is displayed. A trove of fossils has revealed details of how life rebounded after the cataclysm that killed off the dinosaurs. [Frank Verock/HHMI Tangled Bank Studios] © Frank Verock/HHMI Tangled Bank Studios/The Columbus Dispatch/TNS Fern fossil collected from Corral Bluffs, Colo. is displayed. A trove of fossils has revealed details of how life rebounded after the cataclysm that killed off the dinosaurs. [Frank Verock/HHMI Tangled Bank Studios]

It was utter devastation. First came huge earthquakes, then towering tsunamis, then a rain of rock that heated the air to broiling temperatures, followed by global darkness. Temperatures worldwide dropped by 30 degrees, and for years there were no summers. Three-quarters of all the species on our planet were extinguished.

a close up of a rock: This photo provided by HHMI Tangled Bank Studios in October 2019 shows some of the plant fossils retrieved from Corral Bluffs, Colo. More than 6,000 leaves were collected as part of the study to help determine how and when Earth's forest rebounded after the mass extinction event. [Frank Verock/HHMI Tangled Bank Studios] © Frank Verock/HHMI Tangled Bank Studios/The Columbus Dispatch/TNS This photo provided by HHMI Tangled Bank Studios in October 2019 shows some of the plant fossils retrieved from Corral Bluffs, Colo. More than 6,000 leaves were collected as part of the study to help determine how and when Earth's forest rebounded after the mass extinction event. [Frank Verock/HHMI Tangled Bank Studios]

It took place 66 million years ago when a meteorite, a rock from space as big as a mountain, crashed into Mexico's Yucatan Peninsula. Among the extinct were the non-avian dinosaurs. For yet-unknown reasons, the avian dinosaurs — the animals we call birds — survived.

Also among the survivors were a few members of our own group, the mammals. For 140 million years they had hidden in the shadows of the dinosaurs' world. Most were the size of mice and rats, a few reaching the size of raccoons.

A recently published bit of research on a site in Colorado shows how fast things recovered. The site, called Corral Bluffs, is about 60 miles south of Denver. In most places the rock record is marred by geological disruptions; there it was almost continuous for the first million years after the extinction event.

a person standing on a rocky hill: A storm rolls in towards Corral Bluffs, Colo., outside of Denver. The area represents about 300 vertical feet of rock and preserves the extinction of the dinosaurs through the first million years of the Age of the Mammals. The exposure is composed of hard yellow sandstone and mudstones, which represent ancient rivers and floodplains, respectively. [Frank Verock/HHMI Tangled Bank Studios] © Frank Verock/HHMI Tangled Bank Studios/The Columbus Dispatch/TNS A storm rolls in towards Corral Bluffs, Colo., outside of Denver. The area represents about 300 vertical feet of rock and preserves the extinction of the dinosaurs through the first million years of the Age of the Mammals. The exposure is composed of hard yellow sandstone and mudstones, which represent ancient rivers and floodplains, respectively. [Frank Verock/HHMI Tangled Bank Studios]

The site is also rare in that it has good remains of both plants and animals, with fossils found in 120 different levels of the 820 feet of rock exposed. It shows in detail how life came back, much faster than anyone thought possible.

The dates were pinned down based on three markers: the presence of certain species of pollen and spores, volcanic ash beds that could be dated by the radioactive minerals they contained, and flips in Earth's magnetic poles recorded in the rocks.

This photo provided by HHMI Tangled Bank Studios in October shows a collection of four mammal skulls collected from Corral Bluffs, Colo. From left are Loxolophus, Carsioptychus, Taeniolabis and Eoconodon. A trove of fossils has revealed details of how life rebounded after the cataclysm that killed off the dinosaurs. [HHMI Tangled Bank Studios] © HHMI Tangled Bank Studios/Dispatch/The Columbus Dispatch/TNS This photo provided by HHMI Tangled Bank Studios in October shows a collection of four mammal skulls collected from Corral Bluffs, Colo. From left are Loxolophus, Carsioptychus, Taeniolabis and Eoconodon. A trove of fossils has revealed details of how life rebounded after the cataclysm that killed off the dinosaurs. [HHMI Tangled Bank Studios]

Right after the catastrophe, no mammal was bigger than a rat, about 2.5 pounds, living in fern-dominated communities with no trees. That stage lasted about 1,000 years.

Within the next 1,000 years raccoon-sized animals showed up, and there were twice as many species of mammals, living among palm trees.

Over the next 200,000 years nut-bearing plants appeared, and the mammals grew even larger — 50 pounds, beaver-sized — and more diverse.

By 800,000 years after the impact, nutritious legumes (peas and beans) appeared. Mammals reached 110 pounds, 100 times heavier than most that had survived the impact, and complex forests had returned.

In relation to geological time, recovery was nearly instantaneous, but the tale should not comfort those who minimize the man-made environmental disaster developing today. In real time, that ancient recovery took 800,000 years. Are we prepared to wait that long?

Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University.

gnidovec.1@osu.edu

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©2020 The Columbus Dispatch (Columbus, Ohio)

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