Re: Gansus Bird-Dino Connection - Penn Press Release

[Michael Habib <mhabib5@jhmi.edu>]

On Wednesday, June 28, 2006, at 06:14 PM, Tim Williams wrote:

> Michael Habib wrote:
>
> > Frigates can nest in trees, actually, despite not being able to 
> > 'perch' in the technical sense of the word.
>
> By perching in the 'technical sense' do you mean one or more toes is 
> capable of opposing two or more other toes in a prehensile grip?

Yes.

> Nevertheless, the hallux of two modern galliform groups (cracids and 
> megapodids) inserts on the metatarsus at the same level of the other 
> toes.  To use the ornithological term, the hallux is 'incumbent' not 
> 'elevated'.  Megapodes live on the ground and use the long hallux for 
> mound-building, but the cracids (guans, curassows, chachalacas) roost 
> in trees and use the hallux to oppose the other toes.  Cracids would 
> be true perchers, wouldn't they?

Good point, the hallux of modern galliforms, being incumbent, probably 
forms a true prehensile grip (though not a particularly good one since 
the hallux is reduced in size).  Cracids would certainly be true 
perchers.  So I stand corrected on galliforms.  Pelicaniforms and 
cavity-nesting anseriforms would remain as good examples of species 
that do not have a perching foot but utilize arboreal roosts or nests.

In any case, I did not intend to create so much confusion, my original 
point was merely that absence of a prehensile grip in a fossil bird 
(especially very basal ones) does not preclude arboreal habits.

Cheers,

--Mike H.