The extant giant armadillo (Priodontes maximus) is widespread in South America.⁵ Compare Priodontes (Figure 9.1a) with a typical reconstruction of the Cretaceous ankylosaur, Nodosaurus (Figure 9.1b). VIEW ADDITIONAL PICTURE OF PRIODONTES Allowing for the vagaries of reconstructing the appearance of an organism from fossils, Nodosaurus appears quite similar to Priodontes. However, accepted theory would, almost certainly, account for the observed similarity between ankylosaurs and the giant armadillo, not in terms of genetic relationship, but by referring to "gradual adaptation to similar environments." But, if armadillos started evolving from a "small, primitive, generalized" placental mammal after ankylosaurs died out, this process of "adaptation" must have been rapid indeed. The ancestors of Priodontes can be traced through the fossil record all the way back to the Paleocene,⁶ immediately after the ankylosaurs are said to have gone extinct.
A "giant" armadillo (Priodontes) is not even quite as large as the smallest known ankylosaur (Struthiosaurus). But much larger armadillos (glyptodonts), now extinct, survived long enough to be hunted by the pre-Columbian peoples of South America only a few thousand years ago.⁷ Glyptodonts the size of a small car survived into the late Pleistocene (e.g., Glyptodon). Such animals were about the size of Ankylosaurus itself, the largest of the ankylosaurs (the Pleistocene ended only about 10,000 years ago). VIEW A PICTURE OF A GLYTODONT Like certain ankylosaurs, some of these giant armadillos had tail clubs. In both ankylosaurs and armadillos, these clubs could be armed with long, bony spikes.⁸
These observations suggest that paleontologists have created an artificial distinction by classifying Mesozoic "ankylosaurs" as reptiles and post-Mesozoic armadillos as mammals. Given available evidence, and given stabilization theory's assumption that new types of organisms typically arise from precursor forms similar to themselves, the obvious conclusion seems to be that the various forms described as armadillos of the "Age of Mammals" (the Cenozoic Era) are descended from the various forms described as ankylosaurs of the "Age of Reptiles" (the Mesozoic Era).