I love flipping through old paleontology textbooks. Many times the text and images inside them have been reproduced from other sources or bear a close resemblance to similar titles published at about the same time, but every now and then I find something really unusual. Such was the case while I was skimming through H.F. Cleland’s 1916 Geology: Physical and Historical.

While looking for out-of-date ideas on the origin of the first tetrapods I came across a very strange restoration of Dimetrodon (illustration to the left). Dimetrodon was a spenacodontid synapsid, an odd creature that, despite its looks, was more closely related to you and me than to reptiles. Perhaps its most prominent characteristic was the sail that