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Cretaceous Cold Case No. 5: When Evidence Dries Up

This is the fifth post in a series called “Cretaceous Cold Cases” in which the science of taphonomy, or prehistoric forensics, is explained by fascinating cases from the files of Terry “Bucky” Gates, a research scientist with NC State and the
North Carolina Museum of Natural Sciences.

South Africa, 250 million years ago. The United States,145 million years ago. China, 92 million years ago. Madagascar, 66 million years ago. Spain, 1 million years ago.

These are just a few of the instances from my files where incredible graveyards of fossil animals have been discovered. So much time, so much space and so many different kinds of animals separate these deathbeds. Could they be connected? On the surface the answer seems to be no. But I have a different idea. Why? Because like any good detective, once you’ve been out in the field long enough, sometimes you just get hunches.

My name is Bucky Gates, and I’m a taphonomist.

Sometimes it feels like I am chasing a ghost. Always looking for the evidence, but coming up just short of a complete answer. These are the moments that drive me to keep working, to not give up. From the time I first cut my teeth on taphonomy at the Cleveland-Lloyd Dinosaur Quarry I have been hunting for Drought. (I capitalize “Drought” because it is the primary suspect in this cold case file.)

I believe that Drought is the mastermind behind a huge number of fossil deposits around the world, but the problem lies in the fact that Drought – by itself – does not necessarily kill anything. Drought is the puppeteer behind the scenes, enabling killers such as disease, hangriness (aggression brought on by hunger), dehydration, habitat loss, and other minor minions to do its dirty work.

Defining Drought is simple: a reduction in precipitation over an area during a certain period of time. However, connecting Drought to fossil boneyards is much like trying to identify a modern-day serial killer; you never know this nemesis is in your midst until it is too late.

If you have read my previous cases you know it is very hard to determine if Drought had a hand in the formation of a fossil site. Al Capone was brought down by tax evasion. Unfortunately, such an elegant charge cannot be leveraged against Drought. The problem is that the evidence used to support a drought-induced fossil site can also be left by other culprits. Take for instance a gathering of many different kinds of victims in one bonebed.  A flood can also gather different dinosaurs together, as could something like a poisoned watering hole.

Drought can also trap populations, which is not a common occurrence in the fossil record. In one spectacular case a population of ancient boomerang-headed amphibians called Diplocaulus (totally awesome, Google it!) was killed and buried in a very small area. Like other amphibians these animals are extremely reliant upon water, and it seems entirely possible that a prolonged dry spell caused the pond or lake where this population lived to dry up, concentrating the entire group into the center of the last remaining sludgy, unbreathable muck before baking them in the cruel sun. What’s left for paleontologists is a unique opportunity to study the life history of a 250 million year old population.

To be fair, Drought has actually helped our understanding of the life that inhabited the Earth millions of years ago. As easily observable in Africa today, once water becomes scarce in an ecosystem, organisms from all across the landscape come together in an effort to stay near water supplies. This gathering means that animals that normally live in environments unlikely to be fossilized now have a chance to be discovered by paleontologists.

Increased numbers of animals also increases the chances of discovery. If the bones of many victims are eroding from the hillside we are a lot more likely to find the site than another locality that contains only one individual.

Drought is a global phenomenon that toys with the most primal instinct of all life on Earth – the need for water. Its reign extends back to the beginning of rain, and it has caused the death of countless numbers of humans, animals and plants.

But – and here’s the “cup half-full moment” –  it has also provided an important way to attract animals from all across an ecosystem to one place, kill them and bury them for posterity. Without Drought’s influence I cannot even imagine how hollow our knowledge of life’s evolution would be.

We paleo-detectives are, therefore, left with the complicated task of compiling as much evidence as possible, presenting it to the jury, and hoping that the same lines we drew to target Drought will also lead other researchers to the same conclusion.