Posts Tagged ‘Donald Grayson is disingenous’

Peccary Cave in Arkansas

October 21, 2018

Perhaps the best site for Pleistocene fossils in Arkansas is Peccary Cave located in Newton County.  The site was first excavated in 1960s, and a follow-up expedition prospected for fossils again in the early 1990s.  The fossil remains of at least 51 species of mammals have been found here. 4000 specimens of a minimum of 64 individual flat-headed peccaries (Platygonus compressus) were discovered in the cave, hence the name.  The bones of other extinct species excavated from the cave include mammoth, mastodon, bison (Bison antiquus), stag-moose, helmeted musk-ox, tapir, beautiful armadillo, and dire wolf.  There are also remains of extralimital species found here that no longer occur in the region–grizzly bear, pine marten, porcupine, heather vole, and numerous other rodents and insectivores of northern affinities.  Plenty of species still found in the region are represented in the cave as well such as beaver, otter, muskrat, raccoon, coyote, gray fox, opossum, and either mule or white-tailed deer. Reptile and amphibian specimens have been excavated from the cave along with a few human-made artifacts of unknown cultural origin.

Map of Arkansas highlighting Newton County

Newton County, location of Peccary Cave.  

Image result for Platygonus compressus

Illustration of the flat-headed peccary.  Peccaries didn’t use Peccary Cave as a den.  Instead, they either fell inside or their bones were washed into the cave when the nearby creek flooded.  Birds of prey dropped or defecated smaller animals into the cave from overhanging trees.

The fossils represent several different climate phases.  The lowest level contains fossils over 22,000 calendar years BP, a climate phase that includes a weak interstadial and the following early glacial maximum.  Mixed Ice Age woodlands of spruce, pine, and hardwoods interspersed with prairies predominated.  7 different species of squirrels lived in the region then, showing how many diverse habitats occurred here.  Red squirrels and least chipmunks, now absent from the region, preferred spruce forests; gray squirrels, fox squirrels, and southern flying squirrels occur in temperate hardwood forests; woodchucks like meadows; and 13-lined ground squirrels require tree-less plains.  The author of the study discussed below thinks the following glacial maximum caused the entire Missouri Plateau to become inhospitable desert because there are few fossils from the site, dating to between 21,000 calendar years ago-15,000 calendar years BP.  Undoubtedly, the region became more arid during this climate phase, and desert scrub grassland likely predominated, but I think there are alternative explanations for the lack of fossils during this time period here: a) the cave entrance may have become closed and/or b) the barren landscape allowed animals to see the trap entrance and avoid it whereas before it was hidden by thick vegetation and animals frequently fell inside.  Without overhanging limbs there was no perch for birds of prey to drop of defecate the remains of their meals.  Moreover, the nearby creek dried up, so there were no floods to wash fossils into the cave.

The upper level of sediment represents a warm dry interstadial post 15,000 calendar years BP when the region was dominated by grassland.  Bison fossils appear during this phase, and toad fossils outnumber frog bones.  Toads can survive better than frogs in more arid climates.

Kurt Wilson wrote his PHD thesis about the peccary and dire wolf bones found in Peccary Cave.  His paper has interesting information, but it is incompletely researched, and his conclusions are logically flawed.  He believes flat-headed peccaries were always an uncommon species.  Part of his reason for this assertion is based on his incorrect observation that “the southeast is virtually devoid of records (of flat-headed peccaries), except for a dozen localities in Florida.”  Wilson is unaware of 2 sites in north Georgia (Yarbrough Cave and Ladds) and 1 site in coastal South Carolina where fossil remains of flat-headed peccaries have been found.  It is also illogical to assume a species was absent from a region based on its absence in the fossil record.  Large areas of the southeast are devoid of fossils because the local geology is not conducive to fossil preservation, not because animals didn’t live there in the past.

Wilson concludes flat-headed peccaries became extinct due to climate change based on 4 lines of evidence that are easily debunked.

1. He dismisses overhunting by humans as a cause of flat-headed peccary extinction when he regurgitates the tired old claim of Meltzer and Grayson (an archaeologist and anthropologist…not paleoecologists) that there isn’t enough archaeological evidence of human interaction (kill sites) with this species.  I consider this reasoning absurd in the extreme.  99.999…etc% of animals that ever lived on earth left no fossil evidence whatsoever.  It has always seemed unreasonable to me to expect the remains of the final populations of a species that overlapped with man for less than 2000 years to be preserved in the fossil record.  The chances of this happening are tiny.  I’ve noticed Grayson’s recent book published in 2016 is frequently being cited in new papers about Pleistocene vertebrates.  Grayson was blatantly dishonest in this book in the way he characterized a study that rules out climate change models of extinction.  (See: ) Grayson lied and he knows he lied.

2. Wilson assumes flat-headed peccaries became extinct in this region about 22,000 calendar years BP because their remains don’t occur in cave sediment after this date.  (When Wilson writes of extinction in his paper he means regional disappearance or extirpation because he’s aware terminal dates for this species in other regions are 11,000 calendar years ago.  Nevertheless, he clumsily never makes this distinction in his paper.)  He asserts peccaries became extinct here because the climate became too arid for them.  Again, he is basing his assertion on the dubious assumption that the absence of evidence is evidence of absence.  I think flat-headed peccaries were probably even more abundant during the arid climate phase because they were anatomically well-adapted to dry dusty environments.  Flat-headed peccaries had extensive structures in their nasal passages that helped filter dust.  Wilson must be unaware there are at least 9 fossil sites where herds of flat-headed peccaries were buried during sandstorms.  (See: ) This suggests they were common in desert environments.  Flat-headed peccaries may have avoided falling in Peccary Cave after 22,000 calendar years BP because the area around the entrance to the cave was barren and not hidden by vegetation.  None happened to fall in the cave after this date, but that doesn’t mean they didn’t still occur in the region.  Other fossil sites in the region yield the remains of horses, but not a single horse fossil has been found in Peccary Cave.  Horses were likely another abundant species in the region that just happened to never fall in or enter Peccary Cave.

3. Wilson did a stable isotope analysis of 2 flat-headed peccary teeth and concluded they fed upon just a few leguminous plant species, so they became extinct when these limited number of plant species disappeared from the region.  I don’t believe the entire dietary breadth of a species can be determined from such a small sample size.  Moreover, 1 study suggests stable isotope analysis is not at all reliable.  (See: )  Scientists compared the results of a stable isotope analysis of moa bones with actual fossil droppings.  The stable isotope analysis was wrong.  Flat-headed peccary teeth were built to eat grass and tough vegetation.  A species that survived millions of years of climate change didn’t exclusively feed upon just a few species of leguminous plants.

4. Wilson asserts flat-headed peccaries were uncommon and thus vulnerable to extinction.  However, a new genetic study of 12 flat-headed peccary individuals from Sheridan Cave, Ohio, dating to just before their extinction revealed populations of this species were diverse and expanding.  This suggests flat-headed peccaries were common, adaptable, and had a wide geographical distribution until the species’ demise.

Peccary Cave has yielded a wealth of information for paleoecologists, and I’m shocked at how little research has been published about this site.  I’ve been able to find about half a dozen research papers.  There hasn’t been a scientific excavation of the site since 1993, though amateurs are currently pillaging it.  Most of the specimens from this site have not yet been described in the scientific literature, and they are not listed on the paleobiology database. An early report of the site mentions the existence of peccary “droppings.”  Yet, nobody has studied the coprolites (please email me if I’m wrong)–an outrageous oversight.  We could actually find out what flat-headed peccaries ate, instead of guessing based on stable isotope analysis.  I’m not sure the coprolites were even collected and stored in a museum.  There should be hundreds of published papers about this site, not just a paltry 6.  I’ve come across other understudied fossil sites and collections in my research, but this site might possible be the most underappreciated.


Bell, Kenneth; and Lee Davis

“Sinkhole Excavations in Peccary Cave, Newton County, Arkansas”

Arkansas Academy of Science 47(30) 1993

Davis, Lee

“Biostratigraphy of Peccary Cave, Newton, County, Arkansas”

Arkansas Academy of Science 1969

Perry, Tahlia; et. al.

“Ancient DNA Analysis of the Extinct North American Flat-headed Peccary (Platygonus compressus)”

Molecular Phylogenetics and Evolution 2017

Wilson, Kurt

“Late Pleistocene Extinction of the Flat-headed Peccary on the Ozark Plateau: Paleozoological Insights from Peccary Cave”

Iowa State Graduate Thesis 2017




Donald Grayson’s Disingenous Case Against Overkill

January 23, 2017

I almost chose not to read Donald Grayson’s most recent book, Giant Sloths and Sabertooth Cats: Extinct Mammals and the Archaeology of the Ice Age Great Basin.  Grayson is a long time skeptic of the hypothesis that man overhunted Pleistocene megafauna to extinction, and he has authored and co-authored a number of papers explaining his position.  In my opinion overhunting by man is the only explanation for the extinction of Pleistocene megafauna that makes sense.  I’ve read his papers and consider his arguments highly illogical and unfair.  But I did purchase his book because I try to absorb all the knowledge I can about my favorite subject–the late Pleistocene ecology of North America.  I don’t have to agree with an author about everything to enjoy their work.  I saw his chapter on extinction was short, just a small portion of the book, and I assumed he would simply rehash his tired old case against overkill.  However, I was shocked at the way he misrepresented the results of a paleoecological study.  He implies the results of this study support climate change models of Pleistocene megafauna extinctions.  In fact this paper specifically states the opposite.

Image result for Giant sloths and sabertooth cats extinct mammals and the archaeology of the Ice Age Great Basin

Donald Grayson’s newest book.  His chapter on extinction is marred by gross deception.

Don Grayson, photo by Mary Levin, UW Photography, 2011

Donald Grayson is an archaeology professor at the University of Washington.  

On page 287 of the above book, Grayson wrote “…paleoecologist Jacquelyn Gill and her colleagues took a close look at tiny bits of Ice Age history extracted from 3 lakes and marshes in New York and Indiana.”    Grayson fails to mention the data from the lakes in New York was gathered in a study led by Guy Robinson (1).  (I will number the studies mentioned in this blog post and list them below.)  Guy Robinson’s team took samples of sediment from some New York lakes and marshes, radiocarbon dated different chronological layers of it, and measured and analyzed the volume of pollen, charcoal, and dung fungus spores in each layer.  The volume of dung fungus spores is used as a proxy to estimate populations of megafauna.  They determined local extinctions of megafauna were staggered throughout 2 thousand years, and they concluded this ruled out climate change as a cause of the megafauna extinctions.  If climate change caused the extinctions, they believed the extinctions at these different sites would be simultaneous.  Instead the local extinctions occurred at different times at different sites, and it appears as if nomadic humans were overhunting megafauna at 1 site, then moving on to another, though these local extinctions occurred shortly before the Clovis cultural era.  Increases in charcoal while megafauna populations were declining is additional evidence of probable human impact.  Jacquelyn Gill, the lead author of the paper (2) Grayson referred to in his book,  details a similar study of an Indiana lake.  The authors of this study also found that megafauna populations declined before the Clovis cultural era but also before climate caused changes in the local plant composition.  They believe human impacts are still a “plausible” cause of megafauna extinction, and they wrote “our data thus rule out the hypothesis that (i) climate-forced changes in vegetation drove the megafaunal decline, and (ii) no-analogue plant communities were created by megaherbivory.”  Megafauna became locally extinct here before the pollen evidence suggests changes in the plant community occurred.  They believe humans can still be implicated in megafauna extinctions at this site because increases in charcoal indicated humans were setting fire to the landscape during the period of megafauna decline, and there is evidence of human butchery of mammoths in southeastern Wisconsin during this same time period, suggesting that humans were likely hunting them at this location as well.

It is very dishonest of Grayson to imply these studies support climate-change models of extinction when the authors of these studies specifically state the opposite.  He should have at least informed his readers of their conclusions and explain why he has a different interpretation of the data.  The authors of these studies do note that megafauna decline occurred during a warm phase of climate, but they believe, if climate played a role, it had to be some other mechanism besides climate-driven changes in the environment.  The accepted logic behind climate change models of extinction is that changes in climate decreased the plant foods necessary to maintain viable populations of megaherbivores.  These studies show this is not the case.  Moreover, fossil coprolites show the plants Ice Age megafauna ate are still common on the landscape today, and isotopic studies indicate they were not picky feeders, but instead ate a wide variety of foods.  I think the warm climate phase provided a greater variety of edible plant foods for humans, thus increasing human populations which in turn was detrimental to megafauna.

There are many regions in North and South America where the environment did not change substantially during the most recent glacial-interglacial transition including the pampas of Argentina, southern California, and southeastern North America, especially Florida and the coastal plain.  Climate change models of extinction just don’t make sense in these regions.  Most species of megafauna enjoyed continent wide distributions, and they endured 30 glacial-interglacial transitions over the past 2 million years without suffering extinctions, yet they did become extinct about the same time man appears in the archaeological record.  This can’t be coincidence.

Grayson focuses his arguments against overkill on the Clovis blitzkrieg model of extinction.  This model proposes humans rapidly overhunted megafauna to extinction within the 500 year period of the Clovis cultural era.  There is another model of overkill: humans were responsible for overhunting megafauna, but it took place over several thousand years and also involved a change in fire regime and other human impacts.  This is known as the protracted overkill model and it is the one I favor.  Grayson ignores this model.  He doesn’t acknowledge the likelihood that pre-Clovis humans impacted megafauna populations.  I’m sure he would point out the lack of archaeological evidence for this.  His main objection to the blitzkrieg model is also a lack of archaeological evidence…he believes there are not enough kill sites (direct evidence that humans killed a beast) to justify the overkill hypothesis.  This objection is unreasonable.  99.999…etc% of the individuals of a species that ever lived left no fossil evidence at all.  It is ridiculous to expect to find fossil evidence of the last individuals of a species that just happened to be killed by men.  Moreover, Grayson never quantifies how many kill sites archaeologists would need to find before he would be convinced humans were responsible for the demise of the megafauna.  He needs to put an exact number on it or cease his objections.  Despite the odds against it, there are numerous kill sites and evidence of human-butchered megafauna bones.  Grayson dismisses over half of them, sometimes unfairly, though sometimes his skepticism is warranted.

Grayson falsely claims the overkill hypothesis has “little going for it” and he sounds annoyed on pages 279 and 280 of his book when he laments its acceptance in the popular media.  He might be annoyed because in recent years the  overwhelming number of paleoecological and statistical studies suggest man at least played some role in megafauna extinctions.  Grayson glosses over a statistical study led by G.W. Prescott (3) that determined both man and climate played a role in the end Pleistocene extinctions.  But 2 recent studies of worldwide extinction chronology (4) (5) determined extinctions are more closely tied to human expansion than climate change.  In the study led by C. Sandom they note extinctions have been severe in climatically stable regions.  They write: “Human arrival was a necessary factor for extinctions, whereas climate variation was a contributory one, enhancing regionally the effects of anthropogenic impacts on additive rather than synergistic ways.”


(1) Robinson, G.S. ; L.P Burney and D.A. Burney

“Landscape Paleoecology and Megafaunal Extinction in Southeastern New York”

Ecological Monographs 2005

(2) Gill, J.L.; J.W. Williams, S.T. Jackson, K.B. Lininger, and G.S. Robinson

“Pleistocene Megafauna Collapse, Novel Plant Communities, and Enhanced Fire Regimes in North America

Science 2009

(3) Prescott, G.W. et. al.

“Quantitative Global Analysis of the Role of Climate and People in Explaining Late Quaternary Extinctions”

PNAS 2012

(4) Aravjo, Bernardo et. al.

“Bigger Kill than Chill: the Uneven Roles of Humans and Climate on Late Quaternary Megafaunal Extinctions”

Quaternary International 2015

(5) Sandom, C. et. al.

“Global Late Quaternary Megafauna Extinctions Linked to Humans, not Climate Change”

Proceedings of the Royal Society 2014