Dimetrodon

Dimetrodon was the apex predator of its time, the Early Permian, about 275 million years ago. The function of the spines on its back is uncertain, but we know there was a web of tissue connecting the spines into a "fin." The Field Museum has a mounted skeleton of this predator in its Evolving Planet exhibition, and many more specimens including another mount in the research collections of the Vertebrate Paleontology Collection.