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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 + 
phorusrhacoid clade.

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!"