Giant extinct Australian killer geese

[Stephen Wroe <swroe@bio.usyd.edu.au>]

I'd just like to address a popular misconception alluded to by Tim (below), 
i.e., that Miller et al.'s analysis of C4/C3 ratios in Genyornis eggshell 
support the hypothesis that the bird was herbivorous. In fact they do 
nothing of the sort - this study simply demonstrated that the animal either 
ate mostly browse OR it ate mostly animals that ate browse (or a 
combination of the two). Miller had determined Genyornis to be herbivorous 
a priori on the basis of traditional interpretation - hence the confusion. 
Still - this doesn't mean that there wasn't marked variation within the 
family - certainly the skull of Genyornis does not appear to be as large in 
relative terms as in other Thunder birds.

Also - to me the absence of shredding talons and a wickedly curved beak are 
neither here nor there. Many largely carnivorous extant birds lack both - 
as did Diatryma/Gastornis. As Tim points out - the real hurdle for 
advocates of a herbivorous role is the gigantic skull and awesome jaw 
musculature. Following the reasoning of Witmer & Rose - we would expect 
these features to diminish in relative terms in an up-sized avian herbivore 
- but in dromornithids we get the reverse! Another interesting feature 
observed by Murray & Megirian in their original description of the 
Bullockornis skull was an unexpectedly wide gape. Of course this would be 
anything but unexpected in a carnivorous bird. Lastly - the presence of 
gastroliths has also been leveled against a carnivorous lifestyle - I posit 
two items for consideration here - living ratites - which are largely 
omnivorous also carry gizzard stones - but perhaps more significantly - 
gastroliths are now known from the guts of a number of indisputably 
carnivorous non-avaian theropods (its also recently been argued that 
gizzard stones in plesiosaurs were for processing food - not bouyancy control).

Cheers

Steve

"There may be some variation within the family on that score. According to
one source, amino acid analysis of eggshells attributed to _Genyornis_
indicates a herbivorous diet. And dromornithid talons don't appear designed
for shredding prey." - Tim

Steve


Stephen Wroe - Homepage - http://www.bio.usyd.edu.au/staff/swroe/swroe.htm