[1] So far, at least seven species in six genera have been identified: Teratornithidae has only been included in a single phylogenetic analysis, published by Steven Emslie in 1988.

The analysis was conducted using cranial characters of various taxa within the order Ciconiiformes, with a specific focus on Vulturidae (Cathartidae).

This defies some earlier theories that extant condors, swans, and bustards represent the size limit for flying birds.

The fingerbones are mostly fused as in all birds, but the former index finger has partially evolved into a wide shelf at least in T. merriami, and as condors have a similar adaptation, probably in other species, too.

Wing length estimates vary considerably but more likely than not were at the upper end of the range, because this bone structure bears the load of the massive primaries.

Other anatomical features, such as the relatively small and sideward facing orbits and the lower skull, are also consistent with a scavenging live style.