Trust the Coprolites, Not the Stable Isotope Analysis

Scientists analyze the bone chemistry of extinct species to determine what they ate.  This is known as “stable isotope analysis.” Some scientists even claim it’s possible to determine which carnivores outcompeted other large predators based on their stable isotope analysis.  (See:  https://markgelbart.wordpress.com/2015/05/02/surprising-discoveries-of-large-carnivore-dietary-preferences-on-the-pleistocene-mammoth-steppe/ )  I was always skeptical of the broad sweeping claims of these studies because the sample sizes were too small, they rely on too many assumptions, and they use too much dodgy math.  But I never voiced my skepticism.  I thought what do I know?  The authors of these studies are brilliant scientists, and I am just a lay-shmuck.  However, a new study vindicates my skepticism.  Oddly enough, this study was published in the comments section of Quaternary Science Reviews , rather than as a regular article, even though it is a scientific study and not an opinion piece.  The authors of this study examined the coprolites and gizzard contents of 3 different species of extinct moas that formerly ranged throughout New Zealand.  The moa coprolites were associated with the subfossil bones of the birds, so this gave scientists an opportunity to test the accuracy of stable isotope analysis.  They discovered the assumptions they make based on stable isotope analysis are not at all reliable.

Skeleton of the heavy-footed moa.

The environment of New Zealand before man arrived on the islands consisted of southern beech forest mixed with grassland.  The coprolites of the heavy-footed moa (Pachyornis elephantopus) show that if fed in the open grasslands.  The little brush moa (Anamalopteryx didiformis) ate plants the grow in the forest understory, and the giant moa (Dinornis robustus) was a generalist feeder that ate plants of the woods and grasslands.  The stable isotope analysis of the moa bones suggested the opposite–that the little brush and giant moas fed in more open environments than the heavy-footed moa.  The direct evidence shows stable isotope analysis is little more than wild guessing.  There is only 1 way to know for sure what extinct animals ate…the contents of their feces.

Mastodon dung excavated from the Aucilla River, Florida.  We know exactly what mastodons ate in Florida by identifying the contents of their feces.

Reference:

Rawlenee, Nicolas; Jamie Wood, Herve Bocherens, and Karyne Rojere

“Dietary Interpretations for Extinct Megafauna Using Coprolites, Intestinal Contents, and Stable Isotopes: Complimentary or Contradictory?”

Quaternary Science Reviews June 2016

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