A Recent Study of Pleistocene Armadillo DNA Yields 2 Surprising Results

An extinct species of armadillo ( Dasypus bellus ) ranged throughout southeastern North America during the Pleistocene.  (A much larger species, Holmesima septentrionalis, was restricted to Florida and the lower coastal plain.)  Scientists have described D. bellus , known by the common name of beautiful armadillo, as being remarkably similar to the extant 9-banded armadillo ( D. novemcinctus ).  The most notable difference between the 2 species is size–the beautiful armadillo was twice the size on average as the 9-banded armadillo.  The latter species began to expand its range into southeastern North America from Mexico within the last 150 years, and today is very common and on the increase in the region.  In a previous blog entry I hypothesized the 9-banded armadillo was a dwarf mutation of the beautiful armadillo, and it was currently recolonizing former parts of its range.  (See: https://markgelbart.wordpress.com/2012/08/19/is-the-9-banded-armadillo-dasypus-novemcinctus-a-dwarf-mutation-of-the-pleistocene-species-dasypus-bellus/ ) However, scientists were recently able to extract DNA from 2 Pleistocene-aged armadillo specimens, and they determined the history of the 2 Dasypus species is more complicated and even more interesting than previously thought.

An armadillo I saw at Scull Shoals State Park, Georgia.  2 species of similar armadillos occupied southeastern North America during the Pleistocene including this 1.

Scientists extracted DNA from an armadillo specimen found in Brynjulfson Cave, Missouri and from another specimen excavated from Medford Cave, Florida.  (They tried many other specimens but these were the only 2 that still yielded viable DNA.)  They determined the DNA of the Missouri specimen was distinct enough from modern 9-banded armadillo DNA to be considered a distinct species.  So much to my surprise, the beautiful armadillo is not the same species as the 9-banded armadillo.  But the Florida specimen held an even bigger surprise…it was a 9-banded armadillo and it dated to over 10,000 years ago.  This means both beautiful armadillos and 9-banded armadillos lived in southeastern North America during the Pleistocene.  The former went extinct while the latter was temporarily extirpated from the region but has just recently made a comeback.

The scientist who originally described the specimen from Florida noted its similarity to the 9-banded armadillo but chose to identify it as a beautiful armadillo because that was the species thought to occur there during the Pleistocene.  This individual was as large as a beautiful armadillo, showing that size alone is not enough to diagnose correct species identification.  Unfortunately, most subfossil specimens no longer contain DNA due to permineralization or decay.  All the specimens labeled ” D. bellus ” in the scientific literature should be re-labeled as ” D. species ” until scientists make a more detailed anatomical analysis of the genus, so that these 2 species can be better distinguished.

So why did the 2 species disappear from southeastern North America near the end of the Pleistocene?  Cold arid climate cycles probably caused range reductions and local extinctions, but armadillos likely re-expanded during warmer wetter climate phases.  Today, 9-banded armadillos may use manmade roads to facilitate their range expansion because it’s less strenuous to travel along cleared roadsides (though dangerous because highways are littered with armadillo corpses). During the Pleistocene armadillos probably followed trails trampled clear by herds of megafauna. This facilitated range expansion during favorable climate cycles.  The extinction of the megafauna may have played a role in the demise of armadillos that could no longer expand their range after climate deterioration caused extirpations. This isn’t a completely adequate explanation–Florida never got too cold and dry for armadillos.  The authors of the below referenced study suggest frequent manmade fires may have been detrimental to armadillos.  Native Americans set fire to the woods annually.  Modern day fire suppression may be another reason 9-banded armadillos have been able to recolonize former territory.

Reference:

Shapiro, Beth; Russell Graham, and Brandon Letts

“A Revised Evolutionary History of Armadillos (Dasypus) in North America Based on Ancient Mitochondrial DNA”

Boreas August 2014

 

 

 

 

Tags: 9-banded armadillo, beautiful armadillo, Dasypus bellus, Dasypus novemcinctus