First hind toe rudimentary, clawless or absent; its metatarsal bone always present.
Hind extremities proportionally longer with inner toe represented only by a small metatarsal bone.
Consequently the ankle-joint of birds is absolutely cruro-tarsal and tarso-metatarsal, i.e.
Outer toes small and rudimentary, or in some cases entirely suppressed; their metacarpal or metatarsal bones never complete.
The most interesting genera are, however, the Upper Oligocene and Lower Miocene Gelocus and Prodremotherium, which have perfectly selenodont teeth, and the third and fourth metacarpal and metatarsal bones respectively fused into an imperfect cannon-bone, with the reduction of the lateral metacarpals and metatarsals to mere remnants of their upper and lower extremities.