Where the Glyptodonts Roamedby Jonathan DuHamel on May. 19, 2010, under Geology
Imagine a Volkswagen-sized armadillo. Such an animal roamed Arizona during the last glacial epoch and into the beginning of our current interglacial period. Its South American cousin sported a tail with a spiked mace which helped it fend off predators such as saber-toothed cats.
The Arizona Geological Survey has a special report on Glyptodonts by David Gillette.
Gillette writes, “Glyptodonts were 4-legged tanks, pseudo-tortoises with fur, protected by a rigid shell composed of tightly interlocking plates an inch thick and more. The largest glyptodonts weighed a ton, ate plants, and probably spent a lot of time in water, along shores of lakes and streams. They resembled their distant relatives, the armadillos, but the fossil record of these two groups spans tens of millions of years indicating they diverged early in the history of their branch of placental mammals.”
“Glyptodonts and ground sloths should be in the vocabulary of every native Arizonan, because these strange animals were among the Arizonans that lived beside mastodons, mammoths, saber-tooth cats, lions, extinct horses, camels, llamas and more in the North American Ice Age, right here in the desert Southwest. It’s desert here now, but 2 million years ago, these animals lived in well-watered savannas and riparian forests that later dwindled …and left little but these fossils as testament to wet times gone by. This was the ‘glyptodont fauna,’ so named because these armored tanks were at times the most abundant large animal in this bizarre landscape.”
“The story of these pilgrims from South America involves two supercontinents, three continents, two oceans, an island chain, an isthmus, glaciers, and sea level. It begins 200 million years ago, early in the Mesozoic Era, during the time of dinosaurs. Earth’s midsection was mostly ocean, and two huge landmasses occupied the northern hemisphere (Laurasia) and the southern hemisphere (Gondwana). The breakup of Gondwana began then, a process that produced the Gondwana continents: Antarctica, Australia, New Zealand, Africa, South America, India, and Madagascar. South America, the homeland of our armored immigrants, separated from Africa, Australia separated from one side of Antarctica and South America from the other side, and eventually Antarctica took its present, familiar polar position. The other land masses slipped away, in the process creating new ocean landscapes: the Atlantic, Pacific, and Indian Oceans, and with the final isolation of Antarctica, the Antarctic Sea.”
Eventually, North and South America were connected by the Isthmus of Panama which allowed the fauna of each continent to mix. Glyptodonts eventually reached Arizona. “The earliest population, known mainly from southeastern Arizona, became dominant members of the ecosystem. They were small as glyptodonts go, weighing perhaps a quarter to half a ton. These were the progenitors of at least two more species in the United States, and two other species known from single specimens in Mexico. But they all belong in the genus Glyptotherium (groove-toothed beast).” The descendant species, Glyptotherium arizonae, had adults nearly twice as large with weights exceeding a ton. They extended from Arizona to Florida.
One remarkable skull from southeastern Arizona has two elliptical puncture holes, interpreted as the consequence of a fatal attack by a large predatory cat. This skull is on display at the American Museum of Natural History in New York City. Arrows point to the two puncture holes.
Fossil hunters, be on the lookout for scutes, the interlocking pieces of the bony shell. The arrows point to follicles that housed bristles which helped the animal sense its surroundings.
Read the full story: http://www.azgs.az.gov/arizona_geology/spring10/article_feature.html