Re: alvarezsaurid arms

[Nick Longrich <longrich@alumni.princeton.edu>]

>     I doubt that they would be dependent on termites.  I just 
> assumed this would be one of many things Patagonykus would be 
> "digging for" (as well as worms, grubs, tubers, eggs, etc.).  Those 
> claws might have also been good for breaking open rotting trees and 
> logs, even in pursuit of hiding symmetrodonts or other small 
> vertebrates.  I bet they had fairly eclectic tastes.
>                 ------ Ken


re clawed putative avians:

Actually, in the arms and skull the alvarezsaurids best resemble 
specialized digging myrmecophages- that is, it looks like the primary 
selective pressure may have been breaking into the mounds of colonial 
insects for termites and/or ants as their primary food source. The 
forelimbs more closely resemble specialized fossorial myrmecophages 
such as pangolins and some armadillos than anything else out there, 
the hand looks very anteater-like but the rest of the arm doesn't 
(anteaters hook and pull, not scratch). If you hold your elbows 
pointing  back, down, and out (that is with the spine held 
horizontally) and cock the elbow at a ninety degree angle, and hold 
your palms facing towards each other, you'll approximate how 
alvarezsaurs held their arms. Rotate the humerus and extend the elbow 
while flexing the palm and fingers; that's probably the digging 
stroke. It would only be good for relatively shallow excavations, 
probably, and of course the rest of the animal wouldn't fit in the 
hole. Either digging straight down(while sitting) or horizontally 
(while standing against a mound) it probably would have been 
sufficient to break into the galleries. Some armadillos also dig into 
roots and after termites, ants etc. and I think numbats often go 
after termites in logs.
	This isn't to say that's all they would have eaten in all 
cases. The nine-banded armadillo is a specialized myrmecophage in 
part of its range, but in the more northern parts of its range its 
more of an omnivore/insectivore. Aardvarks apparently supplement 
their diet with cucumbers. Some animals may have been more or less 
myrmecophagous- it's dangerous to try to overgeneralize and say that 
all species of a clade, or even all members of a species, were 
specializing (or generalizing) in the same way. Certainly there are 
different takes on myrmecophagy- Aardwolves specialize on a 
particular genus of termite which forages above ground at night, and 
just walk along and lap up the insects. Naturally, they lack the 
specialized digging implements seen in other lineages.


re: putatively clawed avians-
	I thought the whole clawed phorusrhacid idea was pretty cool, 
then I asked Storrs Olson about it back in 97. He said there wasn't 
any fossil evidence for it (and he's in a pretty good position to 
know to say the least), so I went and started digging. The Discover 
article has a nice painting of a clawed phorusrhacid, and it talks as 
if the claws and phalanges and all are fact rather than inference or 
hypothesis, but nowhere in the entire article did it mention the 
actual discovery or existence of phalangeal material for Titanis. So 
I went and dug up the article describing the Titanis wing stuff. 
There's a ball-like joint on the alular metacarpal, and the wrist is 
shaped unusually, and this is interpreted as supporting the presence 
of clawed digits. No mention of actual claw or phalangeal material. I 
was pretty unhappy that Discover would run a cover story on something 
like this and pass it off as fact, rather than hypothesis, but that 
seems to have been what they did, at least as far as I can tell. It's 
also distressing in light of the science media's tendency to stir up 
debate and argument when it suits them (e.g. dinosaurs are/aren't 
birds and the whole carnival there) but when there's actually not as 
much disagreement as made out. In the years since, I have never heard 
anyone actually refer to preserved claws- as in page # and line in a 
peer-reviewed article, figure reference, museum accession number, and 
I've tried asking on this list. Does anyone, anywhere, actually know 
of some real evidence behind this? If not, shouldn't we be treating 
it as an hypothesis, rather than a fact? Personally, I'd love to be 
proven wrong here. Well, strike that, I hate being proven wrong about 
anything, but it'd probably cancel it out to find out that these 
things really did have bigass claws, which would be pretty cool. If 
they  exist, someone somewhere's gotta know where and when and how 
they were found,  if we have all these people who can know whether a 
Outer Kyrghizshani theropod tooth is from the Goniacian or Pithonian 
or whatever.