Mystery in Madagasgar: Fossil Beds

Biological Evolution 
STEM
Environmental and Science Education
Edward Hessler

The mystery referred to in the title of this post would be less of a puzzle had it not occurred so long ago: 70 million years before the present. It involves an extraordinary series of enormous mass graves of dinosaurs of all sizes and kinds and literally cheek to jowl.

In the August 29, 2017 daily letter from the American Association for the Advancement of Science, Science staff writer Carolyn Gramling summarized research in which "researchers proposed a culprit behind this ancient mystery." For this area of Madagasgar, periodic drought has been the default explanation for these animals with burial provided by sediment following torrential rains.

One of the researchers is Raymond Rogers, a paleontologist at Macalester College. He has been studying a site in the Maevarano Formation for twenty years. In Gramling's article Rogers refers to the site he and colleagues have been studying as "the most fossiliferous package of rock I've ever seen."  That particular bed is a "third the size of a tennis court" and has yielded some "1200 specimens."

Rogers and others grew skeptical of the standard explanation. There are large problems. The animals "nestle against each other, suggesting that the bodies were buried where they died and that the killer struck all kinds of animals without discrimination." Clearly, the cause acted fast. And then there was the "arched-back posture of the dead" (suggesting convulsions which is known as hyperextended neck posture), the large number of dead birds and a "carbonate crust, similar to those left by algae in other sediments."

Together these suggested harmful algal blooms (HABs).  There is some previous evidence which Gramling discusses--an 1878 paper "in dead livestock near a lake; testing confirmed that the animals had ingested toxic cyanobacteria" and a recent paper suggesting "that toxic algae periodically killed hundreds of whales and other marine animals off the coast of what is now Chile, starting 11 million years ago."

What is missing is the famous "smoking gun": direct evidence of the algae. The next step Rogers and his team plan is to look for "chemical traces of algae" (biomarkers).

It is a lovely and fascinating research story and also an example of how science works--constantly examining the evidence, wondering about the pieces and suggesting an alternative hypothesis. The original paper is protected by a subscription firewall but the short summary from the research article may be found here.