I find some of the most interesting and surprising topics for my blog from reading obscure scientific journals. I recently discovered Zootaxa, a journal I never encountered in my 18 years of doing research for this blog. I searched through their archives looking for additional topics and found the subject of last week’s blog entry, but in the bibliography of that article, I found reference to yet another surprising paper. Scientists long classified the extinct glyptodonts as relatives of armadillos but not actually armadillos. Glyptodonts were much larger and most likely subsisted on grass, while armadillos mostly eat invertebrates. Glyptodonts had stiff turtle-like shells; armadillos had flexible carapaces. Some scientists noticed anatomical similarities in the skulls and jaws of glyptodonts and small pink fairy armadillos in the Chlamyphoridae Family, and they did suspect a close relationship between the 2. Scientists succeeded in extracting DNA from a 12,000-year-old glyptodont carapace. They were able to map the whole genome. Amazingly, they determined glyptodonts were not just close relatives of armadillos but should actually be classified in the same family as the diminutive pink fairy armadillos.
Surprisingly, the extant pink fairy armadillo, the smallest species of armadillo, is the closest living relative of the huge extinct glyptodonts. Evolution can occur rapidly because scientists believe glyptodonts evolved to their enormous size shortly after divergence from fairy armadillos.
Based on genetic evidence, glyptodonts should be classified with fairy armadillos. From the below referenced study by Delgur et al.
DNA from doedicurus, a type of glyptodont was used in the 2 below referenced studies.
Glyptodonts were about the size and shape of an old-fashioned Volkswagon.
The species of glyptodont used in the below referenced studies belonged to the Doedicurus genus. They were huge animals 12 feet long and weighing 3000 pounds–about the size and shape of an old-fashioned Volkswagon. Some species had spiked clubs on their tails they used for defense and probably battles over mates. Scientists believe the first species weighed just 15 pounds, but they rapidly evolved into a much larger size and a diet dominated by plant matter instead of invertebrates. They diverged from smaller armadillos about 35 million years ago, according to genetic evidence. This evidence is consistent with the fossil record. Glyptodonts first appear in the fossil record about the same time. This rapid evolution is a good example of punctuated equilibrium, a process of evolution marked by isolated episodes of rapid speciation between long periods of little change. I hypothesize the rapid evolution of glyptodonts occurred after some unknown extinction event that left an ecological niche open for a large grass-eating animal.
There are 2 species of extant fairy armadillos–Chlamyphorus truncatus and Calyptophraetus retusus. The former lives underground in a desert area of Argentina where they feed upon insects, worms, snails, and some plant matter. The latter lives in scrubland habitat along the borders of Argentina, Bolivia, and Paraguay. Chlamyphorus is considered endangered; the status of Calyptophraetus is unknown. These types of armadillos can bury themselves in desert sand with surprising speed, but they still fall prey to domestic dogs and cats.
References:
Delgur, F.’ et. al.
“The Phylogenetic Affiliation of the Extinct Glyptodonts”
Current Biology 26 (4) Feb 2016
Mitchell, K. et. al.
“Ancient DNA From the Extinct South America Giant Glyptodont Doedicurus sp. (Xenartha Glyptodontidae) Reveals that Glyptodonts Evolved from Eocene Armadillos”
Molecular Ecology 14 2016
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