Dorsal Vertebrae of the Archegosaurus
Archegosaurus is a genus of amphibian which lived during the Asselian to Wuchiapingian ages of the Permian, around 299-253 million years ago. Pictured here is the dorsal vertebrae.
Encyclopaedia Britannica (11th ed., vol. 3) (New York, NY: The Encyclopaedia Britannica Company, 1910)