So, did this “overwater dispersal” require rafting of the sort always predicted for terrestrial animals, or did they fly? We’ll come back to this issue in the next article. The conclusion from this? They’ve gotten to where they are more recently, (mostly) via overwater dispersal. In short, neither the fossil record nor the pattern of palaeognath or ratite phylogeny supports the idea that these birds were diversifying, or even in existence, at the times required for a vicariant explanation for their distribution. 2014), but even studies of this sort ‘only’ posit palaeognath origins at about 83 million years ago, plus they concern the origin of the lineage that led to both modern palaeognaths and the Paleogene lithornithids (a group of long-jawed, archaic flying palaeognaths), not to the origin of modern-type ratites. As it happens, there are good reasons for thinking that palaeognaths were present in the Cretaceous ( Lee et al. There are no fossil ratites anywhere near this old (the oldest, in fact, are from the Paleocene). Because I’m British, I call these birds palaeognaths (rather than ‘paleognaths’), and this makes sense given that the group is termed Palaeognathae, not ‘Paleognathae’. Together, both are united within Palaeognathae, the bird clade typically imagined to be anatomically (and perhaps behaviourally and ecologically) archaic compared to all other modern birds. However, despite the fact that they were often regarded as neognaths close to galliforms in the past, tinamous clearly share morphological and molecular characters with ratites. 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. All 40 or so species are small compared to ratites, capable of flight, and superficially galliform-like. But there’s another modern group we have to consider here: the tinamous of South, Central and southern North America. 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. Gigantic, long-legged and flightless 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 (specifically, the ornithomimids or ‘ostrich mimics’).Ĭonventionally, 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). 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. 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. Why, precisely, am I re-publishing it now? We'll come back to that later….Īs blasphemous and offensive as it is to say it, birds are pretty samey. And it’s for that reason that I've published the article you’re reading now, originally from Tetrapod Zoology ver 3 (the Scientific American years) where it appeared in March 2014 (that original version is here). Of the several issues tackled in the book, one is the evolution of ratites and their kin.
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