Controversies From the World of Ratite and Tinamou Evolution
by Darren Naish
As blasphemous and offensive as it seems to say it, birds are pretty samey. Generally speaking, they’re small flying things with long forelimbs, proportionally large heads with big, globular braincases, and grasping feet where an enlarged first toe (the hallux) opposes the remaining three. A shape like this was – so both the fossil record and inferences made from cladograms show us – ancestral for modern birds, so any bird that deviates from it is weird indeed.
Cue ratites. Gigantic, long-legged, flightless birds with proportionally small heads, short, ridiculously short, or absent wings, they are the closest that any bird group comes to recapturing the body form (and presumably lifestyle) of non-bird dinosaurs.
Conventionally, the term ‘ratite’ is used for the kiwi-emu-rhea-ostrich clade (even though it always feels a bit weird to regard kiwi as ratites). The 11 or so recently extinct moa of New Zealand and the also recently extinct elephant birds or aepyornithids of Madagascar are also clearly members of this group, and then there are a handful of fossil groups as well.
But there’s another modern group we have to consider here: the tinamous of South, Central and southern North America. All 40 or so species are small compared to ratites, capable of flight, and superficially galliform-like. They lack the anatomical specialisations that make ratites so remarkable, like an unkeeled, raft-like sternum, reduced, atrophied or absent forelimbs, proportionally long legs and neck, loose, ‘decomposed’ plumage, and so on…
(read more: Tetrapod Zoology - Scientific American)
top illustration and bttm photos by D. Naish