Climate change 201 million years ago likely led to worldwide dinosaur dominance
Have you ever watched a bug or a lizard on a cold morning? They remain motionless until the sun warms them. You can pick it up, and it won’t do anything to escape. The viral videos of a Florida iguana on a winter cold-snap is a great example. That’s what it means to be cold-blooded; cold-blooded animals do not generate their own heat, unlike us warm-blooded humans.
Most, but not all, modern reptiles are strictly cold-blooded, and for a long time, it was believed that dinosaurs were as well. Now some fossil evidence suggests that dinosaurs may have been able to regulate their own body temperatures, but it is still very likely that dinosaurs were sensitive to temperature swings associated with climate change. Around 66 million years ago, Earth’s climate changed significantly and finally ended the dinosaur reign on Earth. But for dinosaurs to assume a dominant role on planet Earth in the first place, something must have propelled them to the aristocracy of species domination.
That something is described in a new study published in Scientific Reports. Researchers investigated phosphate-rich deposits that formed in an ancient lake. These deposits changed in composition right before the end-Triassic mass extinction event that occurred 201 million years ago. At the end of the Triassic period, biodiversity was on the decline as evidenced in the fossil record. Dinosaurs were also around, first evolving many millions of years before.
Ooids
So how can ancient lake deposits tell the story of the mass extinction event that opened up an ecological niche for dinosaurs to thrive? To understand that, you need to know the geological context of the deposits, in particular, sediments called ooids (pronounced like it is spelled, oo-ids, where the ‘oo’ sounds like the ‘ue’ in blue). Ooids are small, round particles that form in shallow lakes or marine waters (for example, the Great Salt Lake in Utah and places in the Bahamas, see picture at top). The waters that ooids form in are basic (pH > 7) and rich in calcium carbonate (the minerals calcite and aragonite) or calcium phosphate (the mineral apatite). These deposits can form inorganically, that is through physical processes alone, or organically under the influence of living organisms. In the inorganic example, as water evaporates, the dissolved mineral components are unable to remain in solution and start to grow into crystals. In turbulent waters, rounded grains can form onion-like layers, representing growth rings. Sometimes bacteria can change the water chemistry, which enables biomineralization and forms round ooids, or larger pisoids or oncoids. Modern phosphate-rich ooids form in oxygen-minimum zones where bacteria help create the ooids by cycling between acidic/non-acidic and oxygenated/ deoxygenated waters. Determining if the inorganic evaporative process or the organic biomineralization process formed ancient ooids is a critical step in decoding past environs.
Changes in the water
By measuring the mineral, isotopic, and organic compositions of 201 million-year-old ooids, researchers were able to reconstruct the water chemistry of the lake in which these ooids formed. The ooids developed in low oxygen and slightly acidic shallow water. Interesting, the chemistry of this one lake is similar to the water chemistry of the deep ocean determined in previous research. This is significant because it may mean that much of the water (shallow or deep, lake or ocean) on Earth was extremely harsh for life, leading to a mass extinction.
A change in oxygen levels and acidification of lakes and oceans would have caused a major die-off event. These chemical changes could have been triggered by widespread volcanism — the culprit has been identified as the Central Atlantic Magmatic Province (CAMP) with its massive release of carbon dioxide and other gasses. Approximately 80% of all marine and terrestrial species went extinct at the end of the Triassic, which is the second-largest mass extinction event to have ever occurred on Earth. When the global water chemistry changed and warmed (approximate global average temperatures increased 3 degrees Celsius), the dinosaurs’ main competition, animals such as large crocodilian-like carnivores and other herbivores, died. This opened the door for a dinosaur take-over.
The largest extinction event was the end-Permian event 251 million years ago (96% of marine species and 70% of terrestrial species), and was also caused by climate change brought about by volcanism. In fact, all of the major extinction events were a result of climate change, usually initiated by catastrophic volcanism.
Outlook
The adaptation of life to specific climatic conditions and the response to climate change are considerable, and it doesn’t take much to disrupt a delicate balance. Geologists are similar to historians; we can only know the consequences of our current planetary changes by critically studying past events. The current climate change crisis is the only one in Earth’s history to be caused by humans, or even to be caused by life in general. We know what climate change can do and we know it is happening now. This is why many scientists think that we are moving toward (or even in) the 6th mass extinction event. The air is warming, the oceans are warming, waters are becoming more acidic, deoxygenation events are happening, biodiversity is already on the decline … all the signs are crystal clear.
Aaron Celestian is Curator of Mineral Sciences at the Natural History Museum of Los Angeles. He researches how minerals interact with their environments and with living things, and how those minerals can be used to solve problems like climate change, pollution, and disease.
Title photo was taken by Stan Celestian.
Original Paper
Larina, E., Bottjer, D.J., Corsetti, F.A., Zonneveld, J., Celestian, A.J., Bailey, J.V. Uppermost Triassic phosphorites from Williston Lake, Canada: link to fluctuating euxinic-anoxic conditions in northeastern Panthalassa before the end-Triassic mass extinction. Sci Rep 9, 18790 (2019) doi:10.1038/s41598–019–55162–2
