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S. AMERICAN LANDBIRDS
Oh no, another tangled phylogenetic nightmare. Nick Pharris said...
>Specifically, that cariamas, turacos, caracaras, phorusrhacoids, and
>others represent a distincively South American radiation of birds. Do I
>have that right?
Ron then asked...
> This is news to me - references? And as turacos are confined to
> Africa today, do they really belong here?
The idea that all the taxa Nick mentioned form a single 'basal South
American landbird assemblage' is essentially a Storrs Olson (1985)
theory. Olson suggested that hoatzins, which he regards as
generalised landbirds perhaps well suited as ancestors to later
'basal landbirds' (much the same as _Foro_), could be ancestral to
the seriema-phorusrhacoid clade. Both groups do share an unusual
lateral bowing of the third metacarpal, and Cecile Mourer-Chauvire
has also used this character to support a hoatzin-seriema link. If
this is true, it's cool, for (as I've discussed here before) it might
suggest that free, clawed fingers are primitive for this clade. Take
that with a ***big*** pinch of sodium chloride.
Meanwhile, Olson (1985) also suggests that touracos and falcons are
similar in osteology and might therefore be related, that caracaras
might be related to the hoatzin-seriema group, and that touracos may
belong in the basal landbird assemblage (and therefore be related to
hoatzins and seriemas). A touraco-seriema affinity has most recently
been supported by Robert Chandler based on some morphological and
molecular characters - he covered this at SVP 1997 and has a paper in
prep. (or in press? Matt?). Chandler proposed that vulturids
(=cathartids) were the sister-group to a touraco + seriema +
OK.. now for the speech about empirical evidence. Olson's
suggestions, and his hypothesis that all of these so-called basal
landbirds are interrelated, is an INTUITIVE scenario. It is not based
on cold hard facts or detailed analytical studies - indeed, no
supporting details have yet been provided for any aspect of the
scenario (excepting the metacarpal character cited above) - and
essentially the suggestions are simply ideas based on gestalt
similarities. For example, Olson (1985) literally states pretty much
that, WRT touracos and falcons, "they look similar, so they are
probably related" (NOT a direct quote!!!). Therefore, the ideas
should be regarded simply as interesting speculations that require
testing. Few workers working on the higher-level systematics of
neornithine birds would accept that they probably do represent
reality (that's your cue Gareth..).
"Go away! Beastly things!"