[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: (origin of the palaeognathous palate)

> If the ostrich and emu descended (as it were) from different volant
> ratites, doesn't this challenge the no-neoteny idea for ratite origins.

I'm not sure what you mean. Anyway, before Marshall's abstract, we had 3

- Ratites lost flight several times. (Unparsimonious -- given the known
fossil record, or rather the _lack_ of one.)
- Ratites already existed, and were widespread across Outer Gondwana, in the
Coniacian if not Turonian. (That's a bit early, keeping in mind that the
earliest known neognaths are Campanian and appear to be basal, albeit within
the crown group.)
- Both together. (Unites both disadvantages without adding any advantages.)

Molecular biologists preferred the 2nd, I the 1st possibility; Marshall's
abstract supports the 1st.
        I should mention that the 2nd idea was at least sometimes
presupposed in the derivation of divergence dates; for example, the famous
study by Cooper et al. (Nature, February 2001) that for the first time
sequenced mitochondrial genomes of moa _calibrated_ the tree with the
divergence of moa from other ratites happening 88 Ma ago, at the time when
New Zealand broke off Antarctica + Australia, thus _presupposing_ that moa
ancestors can only have walked to NZ.

> Or, is there something about primitive ratites that
> predisposed them to dominate the flightless niche?

It's easily imaginable that paleognaths, like rails, can more easily lose
flight than other bird clades. The details of embryonic development make
this possible; Feduccia's book has more about this. (But keep in mind that
there isn't just one ecological niche for flightless birds.)