Glyptodont

Glyptodont—The glyptodonts huge, domed carapace made it almost invulnerable to predators. (Natural History Museum at Tring)
Glyptodont—Even if a predator was stupid enough to attack an adult glyptodont, its lashing tail could inflict some serious injury. (Natural History Museum at Tring)

Scientific name: Glyptodonts Scientific classification:

Phylum: Chordata Class: Mammalia Order: Cingulata Family: Glyptodontidae When did it become extinct? The glyptodonts became extinct about 10,000 years ago. Where did it live? The glyptodonts were native to South America, although fossils of a similar animal are known from the southern parts of North America.

South America was once home to a number of glyptodont species, all of which looked like enormous armadillos. These are surely among the most bizarre animals that have become extinct in the last few thousand years, and some of them reached huge sizes. An adult Glyptodon, the typical representative of this group, which used to amble around in Argentina, could have been 4 to 5 m in length and weighed in excess of 2,000 kg, making it as big as a small car.

The short, squat limbs and fused vertebrae of the glyptodonts supported a massive, domelike carapace that must have afforded the living animal a formidable level of protection from hopeful predators. This carapace was composed of more than 1,000 bony plates, each of which was more than 2 cm thick. The head was also heavily protected with a bony plate, as it could not be withdrawn into the carapace like that of a turtle. Not only were the glyptodonts heavily armored, but they also had a fearsome weapon in the shape of their tail. In some species, this was fortified with rings of bony plates, whereas other species sported a thuggish club or dangerous looking, macelike growth. Any predator would have to have been wary of a glyptodont's lashing tail if it were to survive to see another day.

The level of protection displayed by the glyptodont came at a price because it was very heavy indeed. The short, squat legs would only have been able to propel the great bulk of the beast at a very lumbering pace. Bones and the way they fit together allow scientists to estimate how the living animal moved. Simulations of a glyptodont's gait show that it would be struggling to amble along at anything more than around 4 to 5 km per hour. Bones can also give us insight into how the animal went about its everyday life. Glyptodonts only had teeth in the rear of their mouths, but they continued to grow throughout the animal's life. This and the massive, deep mandible, which, in the living animal, was moved by huge jaw muscles, show that the glypotodonts were herbivorous animals that fed on fibrous plant food. Exactly what plants they ate can only be surmised, but perhaps the grasses and low-growing vegetation of the prehistoric South American grasslands were their favored food.

It is not clear what predators the glyptodont's armor was protecting them from. Certainly the fossil record has not offered up any predator that appears to have been powerful enough to kill an adult glyptodont. Saber tooth cats, huge terror birds, and jaguar-sized predatory marsupials all lived alongside the glyptodonts, but it is hard to believe that any of these animals could have gotten the better of an adult glyptodont. Perhaps only the young glyptodonts were vulnerable to predation, as is the case for some of the large mammals that wander the savannah of Africa today.

The causes for the demise of the glyptodonts can only be guessed, but it is extremely likely that they succumbed to habitat changes brought about by shifts in the earth's climate. These bizarre animals appear to have disappeared around 10,000 years ago—around the time the last ice age was coming to an end. It is likely that the first humans in South America hunted glyptodonts, but it is doubtful that this was the cause of their extinction. The glypotodonts' numbers probably declined in the face of changing habitats and it is possible that human exploitation hastened their demise.

♦ The glyptodonts first appear in the fossil record in the Miocene, which spanned a period of time from 5 to 23 million years ago. They are thought to have evolved from an armadillo-like animal, subsequently diversifying and reaching large sizes.

♦ The glyptodonts shared South America with a huge number of very large animals, all of which are collectively known as megafauna. All of the really large representatives of the megafauna became extinct around 10,000 years ago, which is further evidence that there were some global changes occurring, although hunting by prehistoric humans can never be ruled out.

♦ The formidable carapace of the glyptodonts and the intriguing tail weaponry of some species may have been put to good use in fights between males during the breeding season.

♦ North America, like South America, had its own megafauna, but the two groups of animals on these huge landmasses were isolated from one another until a great deal of geological activity formed the isthmus of Panama, effectively joining the two continents around 3 million years ago. This land bridge allowed animals to move between the landmasses, an event known as the Great American Interchange (see the "Extinction Insight" in chapter 2). The glyptodonts took advantage of this bridge and crossed into North America, eventually spawning the species known as Glyptotherium texa-num, whose fossils are found throughout Texas, South Carolina, and Florida.

♦ It is highly likely that the first humans to reach the Americas saw the glyptodonts alive, but we don't know the extent to which hunting affected their numbers. What we know for sure is that certain tribes from Argentina were intimately aware of the animal's fossils. It is said that certain tribes used the huge carapaces as shelters during bad weather. Indeed, the animal still exists in the folk memory of some of these peoples.

♦ Although fossils can tell us a lot about what an animal looked like and how it lived, the bare bones often only give us tantalizing glimpses of the living animal. One such mystery is the glyptodont's reduced nasal passages, which appear to have served as anchoring sites for considerable muscles. This observation has led some people to suggest that the glyptodonts were equipped with some manner of trunk, but as with many paleontological mysteries, we will never know for sure.

Further Reading: Haines, T., and P. Chambers. The Complete Guide to Prehistoric Life. Richmond

Hill, ON Canada: Firefly Books, 2006; McNeill Alexander, R., R. A. Farin, and S. F. Vizcaino. "Tail

Blow Energy and Carapace Fractures in a Large Glyptodont (Mammalia, Xenarthra)." Zoological

Journal of the Linnaean Society 126 (1999): 41-49.

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