Sphenacodon, like his cousin Dimetrodon, was a Pelycosaur
and not a dino. Like Dimetrodon, Sphenacodons were top predators of their time, their fossil record extending from the Latest
Carboniferous through to the early Middle Permian.
Though one usually thinks of a sail-backed (or 'finned') creature when thinking of a Pelycosaur,
Sphenacodon didn't sport the sail like Dimetrodon or Edaphosaurus. He did, however, have long, vertebral spines that did probably
give him a ridge down his back.
Two species of Sphenacodon are known: S. ferox and S. ferocior. Marx's figure
is most likely a representation of the latter, as the vertebral spines in the former were not as pronounced as were those
in ferocior. Ferocior was also a more robust creature than ferox.
O.C. Marsh named Sphenacodon 1878. The first fossils were found in New
Mexico by David A. Baldwin.
The Zallinger-esque Sphenacodon is (in my humble opinion, anyhow) one of the coolest
Marx figures. The only other Spenacodon figure I know of was made by a company called Linde (it was a 1950s coffee premium
and these are quite rare).
Ol' Sphen just seems to always get overshadowed by the 'sailbacks,' Edaphosaurus and Dimetrodon--for