Posts Tagged ‘G. floridanus’

Specimen # F: AM 95737

November 2, 2011

Photo of a Glyptodont skull with puncture holes made by the bite of a species of fanged cat, probably a western dirktooth.  This fossil is at least 1.8 million years old.

The Frick Collection in the American Museum of Natural History includes a remarkable specimen catalogued as F: AM 95737.  One lucky fossil hunter found this skull of a juvenile glyptodont at the 111 Ranch in Graham County, Arizona.  It’s a complete skull minus a few missing lower molars.  This alone makes it unusual because most excavated fossils consist of disarticulated pieces.  Holes in the skull inflicted by a fanged cat make this discovery all the more fascinating.  This species of glyptodont is Glyptotherium texanus, a species which dates to the Blancan Land Mammal Age, a stage that ended early in the Pleistocene 1.8 million years ago.  G. texanus is believed to be ancestral to G. floridanus, the species of glyptodont that lived in southeastern North America from 300,000-11,000 years BP.  The species of cat that apparently killed this baby glyptodont can’t be determined with certainty, but it was probably a western dirktooth (Megantereon hesperus), a species ancestral to the Rancholabrean era species’ Smilodon fatalis and Dinobastis serum (the scimitar-toothed cat).

The dirktooth evidentally attacked this young glyptodont from the front.  Scientists consider this unusual because most cats assault their prey from the rear.  In addition to their armored skull adult glyptodonts had a tough cephalic shield protecting their skull, but the cephalic shield was undeveloped in the young, explaining how a western dirktooth’s bite was able to penetrate through to the brain.

The glyptodont skull was found associated with other fossils, including those of one and three-toed horses (Equus and Nannihippus), hares, and more tellingly capybaras and giant tortoises.  The latter two species indicate a subtropical to tropical climate.  Climatic patterns were quite different during the Pliocene and throughout much of the Pleistocene.  Southwestern North American enjoyed a wet lush environment then, unlike the desert of today.  Lots of lakes and marshes dotted the landscape.

Illustration of a glyptodont.  More than one description in the literature compares the size and shape of this beast to a Volkswagon.  They weighed up to a ton.  Note the stiff turtle-like shell and wide spreading feet.

The glyptodont was a bizarre mammal resembling a turtle.  It’s closest living relatives are the other edentates–armadilloes, anteaters, and sloths.  Armadilloes also have armor, but theirs is flexible.  Glyptodont armor was stiff and turtle-like.  Scientists don’t know if it could withdraw its head inside when threatened.  They were adapted for living in flat, marshy terrain.  Their feet spread wide enabling them to stand on and traverse muddy marshy ground, but they were unable to climb up hills.  The range map below suggests they inhabited coastal lowlands and flat river valleys.  They expanded their range during warm interglacials and interstadials, and conversely their range contracted during cold arid stadials.  They inhabited dense vegetation in marshes and swamps which predators avoided because of difficulty in gaining traction and perhaps mosquitoes.  Mosquitoes may not have been able to penetrate glyptodont armor.

Map of fossil sites where remains of G. floridanus have been found.  This is from the below referenced paper.  This map was drawn in 1981 before a glyptodont fossil was discovered in Louisiana.  I added that locality to the map.  Note the latitude of some of the inland sites.  This suggests that during warm interglacials glyptodonts colonized wetlands in upper river valleys.  They may have periodically occurred as far north as what’s now Augusta.

Glyptodont fossils are often found associated with fossils of capybaras and giant tortoises, indicating they occupied the same kinds of habitat.  Glyptodont teeth even resemble capybara teeth, though the former lack enamel.  Glyptodonts are in the edentate family.  Edentate translates to toothless, but they aren’t actually toothless–their teeth simply have no enamel.  Of the three only giant tortoises could occupy drier habitat.  Glyptodonts and capybaras required subtropical or tropical climate because they both fed upon succulent green vegetation, and they couldn’t survive on winter-killed or dormant plants.

Photo of capybaras by a lake shore.  Extinct species of capybaras shared the same habitat with glyptodonts.  Capybaras are the world’s largest rodent, but during the Pleistocene in North America they were second to the giant beaver.

The authors of the below referenced paper suspect a commensal species of bird, like an oxpecker, existed during the Pleistocene and it fed on external parasites formerly found on glyptodonts.

Reference

Gillette, David; and Clayton Ray

“Glyptodonts of North America”

Smithsonian Contributions to Paleobiology #40 1981

Note: I mentioned this specimen in my book but couldn’t remember where I read about it and didn’t include it in my bibliography.  I was happy when I finally find this paper which is available online as a pdf download.