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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The Real Big Birds of the Pleistocene

I was a little too old for Sesame Street when PBS finally began broadcasting in northeastern Ohio circa 1972.  Nevertheless, I watched the show because it was something different.  Then, we didn’t have hundreds of satellite and cable networks, let alone a youtube that allows a person with internet to access millions of any kind of videos they can think of.  Instead, we were limited to the Cleveland and Youngstown affiliates of ABC, CBS, and NBC along with independent uhf channels from Pittsburgh and Cleveland.  The independent Pittsburgh station offered Rocket Robin Hood cartoons and poster board representations of Marvel superheroes that had audio dialogue.   The independent Cleveland station showed Shock Theater–double features of B movie horror flicks.  One had to endure a fuzzy reception to enjoy either station.  So Sesame Street was a kind of novelty compared to the limited options available then.

Big Bird, the iconic character who lives in the fictional world of Sesame Street, is much more famous than some real life big birds that lived from before the Pleistocene until well into the Holocene.

The fictional big bird of the PBS series Sesame Street is supposed to be 8’2″ tall.

Elephant birds were the largest species of bird to ever walk on earth.  They lived in Madagascar until ~1800 AD.  Humans likely overhunted them to extinction.  The largest species of elephant bird, Aepyornis maximus, grew as tall as 10 feet and could reach weights of 1100 lbs, and their eggs weighed 22 lbs.   There were 2 genera of elephant birds–Aepyornis and Mulleronis.  Scientists dispute the number of species in the Aepyornis genus.  Some think there are 4 species; others suggest all the fossil material belonged to just 1 species.

Illustration of the extinct elephant bird (Aepyornis maximus). 

Moas were another species of big bird that rivaled the fictional Big Bird of Sesame Street in size.  There were 11 species of moas native to New Zealand, the largest being Dinornis robustus.  It grew to 6’6″ tall and weighed over 500 lbs.  Humans reached New Zealand about 1400 AD, and they overhunted moas into extinction within 200 years.  Archaeologists have discovered big piles of moa bones in human settlements, and the extinction of these birds is considered an excellent case study of humans overhunting species of vertebrates to extinction.

11 species of extinct moas roamed New Zealand until humans overhunted them into extinction.  They did not use bows and arrows as the illustration depicts.

Elephant birds and moas belong to a family of birds known as the ratites which also includes ostriches, emus, cassowaries, rheas, kiwis, and tinamous.  All of these species, with the exception of tinamous, are flightless ground dwelling birds.  The ratites live on continents that were once part of the supercontinent Gondwanaland.  Formerly, scientists believed the ratites shared a common ancestor from when Africa, Australia, and South America were part of Gondwanaland and later evolved into different species after Gondwanaland split apart.  I mentioned this belief in my post about the temporary ostrich colonization of India during the Pleistocene. (See: https://markgelbart.wordpress.com/2015/09/24/ostriches-struthios-sp-occurred-in-india-during-the-late-pleistocene/ )  However, a new study of ratite DNA determined tinamous, birds that can fly, are closely related to the extinct moas.  (Tinamous were thought to be distant sister taxa to the ratites before this study.)  This finding suggests each species of flightless ratite independently evolved flightlessness from birds that flew to each southern hemisphere continent after Gondwanaland split apart. This is the best explanation for the close relationship between the tinamous and the moas because it’s unlikely that flightless birds would re-evolve the ability to fly.  These speciation events occurred when the continents were closer than they are today, so that the distances were easier for flying birds to traverse.  After a population of tinamou-like birds established a colony on a new continent, they encountered an ecosystem that had just recently lost dinosaurs to the K-T extinction event.  The ratites evolved as an ecological replacement for at least some of the dinosaurs in regions where birds faced less competition from mammals.

Proposed evolutionary relationships between the ratites based on molecular DNA evidence.

There are 47 species of tinamous.  They are native to South America, Central America, and southern Mexico.  They nest on the ground but will roost in trees and are omnivorous, feeding upon fruit, plant matter, insects, worms, and herpetofauna.  There are some anatomical similarities that suggest tinamous are related to other ratites, but if not for DNA evidence, scientists would never know that they are ratites themselves.

Brushland tinamou (Nothoprocta cinerascens).  Tinamous are closely related to extinct moas of New Zealand.  Because they can fly, scientists consider this evidence that all flightless ratites evolved independently from birds that were able to fly over ocean water.

Reference:

Mitchell, K.J.; et al.

“Ancient DNA Reveals Elephant Birds and Kiwis are Sister Taxa and Clarifies Bird Evolution”

Science 344 2014