Crassigyrinus

Crassigyrinus (from , 'thick' and , 'tadpole') is an extinct genus of carnivorous stem tetrapod from the Early Carboniferous Clackmannan Group of Scotland and possibly Greer, West Virginia.

==Discovery== The type specimen was originally described as Macromerium scoticum and lacked a complete skull. With subsequent discoveries, Crassigyrinus is now known from three skulls, one of which is in articulation with a fairly complete skeleton, and two incomplete lower jaws. Crassigyrinus grew up to in length, coupled with tiny limbs and unusually large jaws. Crassigyrinus is taxonomically enigmatic, having confused paleontologists for decades with its apparent fish-like and tetrapod features. It was traditionally placed within the group Labyrinthodontia along with many other early tetrapods. Some paleontologists have even considered it as the most basal crown group tetrapod, while others hesitate to even place it within the Tetrapoda superclass.