RE: Arboreal Theropods: The prize at the bottom of the cracker jack box

[Jason Brougham <jaseb@amnh.org>]

One more possibility occurred to me today.

Though Dr. Habib assures us, and I believe him, that even gliders use leaping 
to gain their initial velocity, and that nothing just drops from an elevated 
position to gain gravitational acceleration, there is a pattern with some sea 
birds.

Procellariiforms (petrels) lack halluces and they nest on the ground (though 
tree nests of Pelecanoides have apparently been reported). When fledging the 
chicks of several species climb trees, in some cases favoring those that are 
tilted at 30 degrees to vertical, and then launch out to sea from this elevated 
position.

Another group of birds with no halluces - murrelets (Marbled Murrelet) - may 
nest on branches in very tall old - growth trees. Before they can fly the 
chicks spend many weeks on the branches, snapping at insects, preening, 
flapping their wings, and so on. When ready to fledge the chicks leap from 
these branches and may fly over 30 km. I wouldn't call marbled murrelet chicks 
arboreal, yet they do successfully occupy tree canopies.

I come to two conclusions.

1) Birds with no halluces still use trees as crucial habitats in their biology.

2) Trees may even be important to birds that nest on the ground and forage at 
sea! Now there's a category outside of G and GB for you!


In any case, there is the possibility that basal paravians utilized trees in 
similar ways, to assist them in gaining range on fledging or on flights (or 
glides) as adults. This could be true even if they were distinctly NOT arboreal 
in foraging or nesting. 

I have tried to always be clear that trees need not have been involved in basal 
paravian evolution. I am not trying to put them in trees. I have tried to 
demonstrate that there are exceptions to the rules that others have cited in 
claiming that such ecomorphologies were IMPOSSIBLE for animals without 
unambiguous specializations. Thus I have tried to promote the proper scientific 
uncertainty and open - mindedness on this issue.