Dimetrodon (Dai-meh-truh-daan) is a large four-legged carnivore that lived during the Early and Middle Permian in what is now North America and Europe. Its name means “two measures of teeth” in reference to the long and short teeth found in its jaws. While you’d be mistaken for thinking this animal is a reptile, it’s actually a synapsid, part of the same lineage represented solely by mammals today. Easily the most recognizable feature of Dimetrodon is its characteristic sail. Many ideas regarding its function have been tossed around, from thermoregulation to display to allowing other Dimetrodons to identify males and females of their species. In reality, it’s likely the sail served multiple purposes, but exactly what these were is still up in the air. What do you think Dimetrodon could have used its sail for? The species in front of you is Dimetrodon grandis, which is common in museums today and is the second-largest known Dimetrodon species (the largest is D. angelensis, and the smallest is D. teutonis!) It lived in the Red Beds of Texas and Oklahoma, USA (a wetland at the time), hunting animals such as Edaphosaurus and Diplocaulus, and alongside Calamites trees and the freshwater shark-relative Xenacanthus!