When Sand Dunes Buried Herds of Flat-headed Peccaries

Peccaries, also known as javelinas, are ungulates in the order artiodactyl.  They are classified in the suborder Suina which includes 3 families–Tayassuidae (peccaries), Suidae (true pigs), and Hippopotamidae (hippos).  Two now extinct species of peccaries were common in North America during the Pleistocene.  Fossils of the long-nosed peccary (Mylohyus nasatus) have been recorded from Florida north to New York and west to California.  This species was the size and shape of a white-tail deer.  Fossils of the flat-headed peccary (Platygonus compressus) have been found from Florida north to New York and west to California and even the Yukon.  During warm interglacials the still extant collared peccary (Peccari tagaeu) ranged into Florida and probably the coastal plain of other southeastern states.

Illustration of flat-headed peccary (on the left) and long-nosed peccary (on the right).  The size in this illustration is misleading.  Long-nosed peccaries had longer legs, but flat-headed peccaries were generally twice as heavy.  A study of 4 individual flat-headed peccary skeletons estimated they ranged in weight from 260-360 pounds.  An average long-nosed peccary usually weighed in at 150 pounds.

Because the ranges of the 2 common species of Pleistocene peccaries overlapped so extensively, and both species are often found in the same fossil sites, scientists have long proposed a difference in habitat preference between them.  However, to the best of my knowledge, there are no in depth studies examining this interesting ecological differernce.  After reviewing the available literature, I’ve reached what I believe is an orginal hypothesis of sorts:  Populations of flat-headed peccaries increased during stadials and decreased during interstadials, while the opposite is true for long-nosed peccaries.  My reasoning is based on evidence discussed below.

1. Flat-headed peccaries were an Ice Age mammal well adapted to cold, dry, and dusty environments.  An anatomical characteristic within their snout helped them breathe in an environment where sandstorms were frequent.  Their fossil remains are often found in herds that died when they were buried by windblown silt, known as loess.  Fossilized herds of flat-headed peccaries buried by loess and/or eolian sand have been found in Kentucky, Colorado, Kansas, Michigan, 2 sites in New York, and 3 sites in Ohio.  The site in Hickman, Kentucky is located in the extreme southeastern corner of the state not far from the Mississippi River.  During stadials, which were particularly cold stages of the Ice Ages, much of earth’s moisture became locked in glacial ice, fostering arid climate.  Rivers shrank in size, exposing mounds of sand and sediment.  Frequent cold winds blew this sand away from the rivers, creating great dunes.  Herds of peccaries often sought shelter from winter winds and gathered beneath overhanging loess deposits on the eastern side of the dune.  The sand dunes did provide protection from this westerly wind, but unfortunately for the peccaries, on occasion the wind caused the top part of the dune to slump on top of the poor beasts, burying them until their accidental discovery by humans some 20,000 years later.  In another scenario the herd of peccaries might get trapped on the western side of the bluff in a sandstorm and become buried because the bluff acted as a barrier that allowed the sand to pile up and over the herd. That so many fossil herds of peccaries have been found in these situations is evidence they were common during stadials when eolian dunes rolled across the landscape.

Platygonus compressus skeleton.  Herds of flat-headed peccary skeletons have been found buried in sand at 9 or more sites.

2.  The Chacoan peccary (Catagonus wagneri) was discovered as a fossil in 1931, then as a living species in 1970.  It’s considered a very close relative of the flat-headed peccary, and it probably inhabits a similar environment that would have been favored by its Ice Age cousin.  The last 3000 Chacoan peccaries live in impenetrable thorny forests.  Not coincidentally, arid climatic conditions of stadials meant the frequency of thunderstorms was greaty reduced.  Without thunderstorms, lightning-ignited wildfires were rare.  Without fire, thorny scrub forests predominated over many square miles.  Large herds of aggressive peccaries making a defensive stand in thick brush must have been difficult for predators to subdue.  That’s not to say, thorny scrub forest was the only type of environment on the landscape.  Grasslands and pine and spruce forests still existed, but scrubby growth covered a greater extent of the landscape than it did during interstadials, and this type of vegetation made a happy home for flat-headed peccaries.

A Chacoan peccary.  It’s very closely related to the extinct flat-headed peccary. It’s favorite habitat is impenetrable scrub thorn forests.  Scrub forests were common in North America during stadials because lightning-ignited wildfires were rare.  Like its living relative, flat-headed peccaries probably loved living in thickets where herds of them could make defensive stands against large predators.

A Chacoan scrub thorn forest.  Parts of North America may have looked something like this during Ice Age summers because the climate was dry and fire was rare.  Without thermal pruning forests and grasslands can become brushy like this.

By contrast, long-nosed peccaries were a slender animal built for running through open woodland.  They survived during stadials in relic habitats where open forests still remained.  Their favored habitat expanded during interstadials and interglacials when glaciers melted and released moisture into the atmosphere spawning lightning-induced fires that burned through scrubland, clearing it and creating open woodlands.  During interstadials long-nosed peccaries were the common javelinas while flat-headed peccaries were reduced to relic status, finding suitable habitat mostly on sandy soils with sparse vegetation where fires were absent and scrubby plant growth prevailed.

Reference:

Finch, Warren; Frank Whitman, John Sims

“Stratigraphy, Morphology, and Paleoecology, Peccary Herd, Kentucky”

Geological Survey Professional Paper 790 1972

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