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 Page-Ladson Site in Northwest Florida

During the late Pleistocene sea level contracted because much of earth’s atmosphere was locked in glacial ice.  The land area of what today is Florida doubled in size, and shorelines extended 50-100 miles west into the Gulf of Mexico.  The water table fell and many present day small rivers did not yet exist.  Instead, the land was pockmarked with many spring-fed ponds that attracted herds of megafauna and other wildlife.  The basal chemistry of these waters preserved bones and organic matter, and later when water tables rose, the Aucilla River began flowing and it covered these ponds with sediment.  The Aucilla River flows over 4 known Pleistocene pond sites–Page-Ladson, Latvis-Simpson, Sloth Hole, and Little River Quarry.  These sites contain deep layers of mastodon dung deposits.  Bones and artifacts are often mixed with the ancient piles of turds, and tracks are also visible where mastodons stepped on their own shit.  Scientists studied the dung and identified the plants mastodons ate.  Their favorite foods in Florida were cypress and buttonbush twigs and cones, but they also fed heavily on aquatic plants, oak leaves and acorns, and fruit including persimmon, plum, crabapple, grape, pokeberry, and wild squash.  At Latvis-Simpson a female mastodon skeleton with a fetus was excavated from a dung deposit.  Other dung deposits contain stone and ivory tools made by humans.

Location of the Aucilla River. This river didn’t exist until about ~13,000 years ago.  It cuts through the site of spring-fed ponds that attracted megafauna, and eventually humans for thousands of years.

A mastodon tusk.  Cut marks on a mastodon tusk found at Page-Ladson suggests humans butchered it for a fatty chunk of meat.

 

 

 

 

 

 

 

Radiocarbon dating of dung deposits at the Latvis-Simpson site indicated the oldest layer goes back to 32,000 BP.  The Page-Ladson site is not as old, but deposits there show man overlapped with megafauna as early as 14,550 years ago, predating the Clovis era.  The list of species remains found at the Page-Ladson site (just some of the fauna that overlapped with man) includes 2 species of gar, 2 species of pickerel, 5 species of catfish, 2 species of suckerfish, 7 species of bream, largemouth bass, black crappie, 3 species of frog, amphiuma, siren, Fowler’s toad, snapping turtle, an extinct subspecies of box turtle, gopher tortoise, an extinct species of giant tortoise, rattlesnake, alligator, great blue heron, pied-billed grebe, cormorant, Canada goose, duck, bald eagle, an extinct species of eagle, California condor, an extinct species of stork, red-shouldered hawk, red-tailed hawk, mourning dove, opossum, beautiful armadillo, pampathere, Jefferson’s ground sloth, Harlan’s ground sloth, raccoon, black bear, river otter, margay cat, bobcat, dire wolf, domestic dog, fox squirrel, beaver, muskrat, Florida muskrat, porcupine, capybara, mastodon, mammoth, bison, large-headed llama, stout-legged llama, white-tailed deer, long-nosed peccary, flat-headed peccary, horse, and tapir.  Remains of the extinct Florida spectacled bear have been collected from other Aucilla River sites, and large carnivores such as saber-tooths and jaguars left remains throughout much of the state’s other fossil sites.  Mastodon remains outnumber mammoth remains by a ratio of 4 to 1 at Aucilla River sites.  The former preferred aquatic wooded habitats, while the latter liked grassy open plains.  Remains thought to be of domestic dog may actually be coyote bones because the 2 species are difficult to distinguish from just skeletal remains.

My Georgia Before People blog was in part inspired by information gathered by the scientists who excavated the Aucilla River fossil sites.  So of course, I must highlight a new study of the Page-Ladson site.  Radio-carbon dates of organic material associated with human artifacts have long yielded dates in excess of 14,000 calendar years.  Many archaeologists dismissed these dates…they assumed error in the dating.  This new study was exhaustive–the scientists took 71 radiocarbon dates using the most modern methods–and they determined humans began frequenting the pond 14,550 years ago.  They confirmed that a mastodon tusk found here showed clear evidence of human butchery.  There are 2 additional examples of human butchering megafauna from Aucilla River sites.  Humans likely used these water sources opportunistically to specifically hunt big mammals.

The study also looked at sporormiella volumes.  Sporormiella is a fungus that grows on dung, and it can be used as a proxy for megafauna abundance.  Sporormiella volume spiked 13,700 years ago but then declined, and apparently the local megafauna became extirpated from the region by 12,600 years ago. This is within the accepted terminal extinction dates for Pleistocene megafauna.  Sporormiella volume briefly increased again about 10,000 years ago.  Researchers attribute this to a temporary migration of bison into the region, though this is based on the assumption that other species of megafauna were extinct by then.  I don’t agree with this assumption and believe local populations of now extinct Pleistocene megafauna persisted until the early Holocene but at levels so low they are difficult to detect in the fossil record.

The sporormiella spike at 13,700 is about 800 years after the first appearance of man in the region.  The entrance of man is also associated with an increase in charcoal from man made fires, and I might add, a change in climate to more frequent lightning storms.  I propose anthropogenic fires improved habitat for megafauna leading to an initial increase in megafauna populations.  But man eventually hunted these species to extinction.  As Gary Haynes proposes, the long term drought that occurred during the Younger Dryas cold snap likely concentrated megafauna around dwindling water sources, making them more vulnerable to human overhunting.

References:

Halligan, Jessi; et. al.

“Pre-Clovis Occupation 14,450 Years Ago at the Page-Ladson Site, Florida and the Peopling of America”

Science Advances May 2016

http://advances.sciencemag.org/content/2/5/e1600375

Webb, David (editor)

The First Floridians and the Last Mastodons: the Page-Ladson Site in the Aucilla River

Springer 2006

Mastodons and Wild Plum Thickets

I found this thicket of wild Chickasaw plums in south Richmond County, Georgia.  The thicket covers at least 2 acres.

Wild plum thickets abound over much of North America.  They’re a pioneer species, growing extensively in old overgrown fields before other trees eventually shade and thereby outcompete them.  The lifespan of a plum tree seldom exceeds 20 years anyway, which is the length of time a plum thicket lasts during its stage of forest succession.  Plum thickets are a common site along roadsides in Georgia and other southeastern states.  For various reasons highway crews often clear corridors on the sides of roadways, and plums thrive in the sunny locations when overstory trees ares stripped or removed.  Today, birds and small mammals such as oppossums, raccoons, and gray foxes eat the fruit and spread the seeds in their feces.  American Indians also extensively planted plums around their settlements.  The variety of plum in the above photograph is known as the Chickasaw plum (Prunus angustifolia), and it is believed to have been originally cultivated by the Chickasaw Indians.  They spread the variety east from their early settlements.

There are 3 species of wild plums that range into Georgia, including south Richmond County where I found the plum thicket pictured above.  I used photographs from google images to compare and distinguish between the 3 and determined that the ones I found were probably Chickasaw plums, though I’m not a trained botanist, so I don’t know for sure.  The other 2 species are the American plum (Prunus americana) and the hog plum (Prunus umbellata).  I harvested a pint of the Chickasaw plums (I could’ve collected bushels.)  They are as sweet and  tasty as the best quality cultivated plums one can buy at a supermarket.  The only drawback is the small size–they’re a little smaller than cultivated cherries and the fruit to pit ratio is even smaller.

Picture of mastodons from google images.

Photo of Mastodon dung recovered from the Aucilla River.

Scientists examining 14,000 year old mastodon dung from the Aucilla River in north Florida found plum pits.  Chemical tests of fossil mastodon bones found at the site determined that mastodons wandered back and forth from north Florida to central Georgia.  These wide-ranging behemoths spread fruit and seeds of many plant species far and wide.  Most of the seeds that went through their alimentary tracts were not only still viable, but they had the added bonus of being encased in fertilizer when excreted.  (See also my blog entry “Paw Paw: Favored Fruit of the Mastodon” which I think is either in my May 2010 or April 2010 archives.)

The dynamic landscape of the Pleistocene included natural environments in all stages of forest succession.  Disturbances and atmospheric conditions such as fires, storms, megafauna foraging, insect damage, disease, floods, beaver activities, drought, and low CO2 levels contributed to frequent formation of meadows, prairies, and savannahs–all suitable environments for plum thickets.  With mastodons (and giant ground sloths) facilitating their spread, plum thickets must have been just as common then as now, if not more so.

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This is an addendum to my last week’s rant about the environmental destruction that white slave-owners inflicted upon Georgia in the early 19th century.  My favorite poem is the lyrics to the rock group, Rush’s song “The Trees.”  Rush is a fantastic group, if you can get past the high voice of the lead singer.  It’s amazing that just 3 people can put out the amount of sound they do.  Anyway, here are the lyrics.

“The Trees” by Rush.

There is unrest in the forest

There is trouble with the trees

For the maples want more sunlight

and the oaks ignore their pleas

The trouble with the maples

(and they’re quite convinced they’re right)

They say the oaks are just too high

and they take up all the light

But the oaks can’t help their feeling

if they like the way they’re made

and they wonder why the maples can’t be happy in their shade

There is trouble in the forest

and the creatures all have fled

as the maples scream “oppression!”

and the oaks just shake their heads

So the maples formed a union

and demanded equal rights

“The oaks are just to greedy; we will make them give us light”

Now there’s no more oak suppression

for they passed a noble law

and the trees are kept all equal by hatchet, axe, and saw