RE: Phorusrhacids killing large mammals in National Geographic Channel

["John Scanlon" <riversleigh@outbackatisa.com.au>]

Bringing up Gastornis/Diatryma beak shape and diet automatically involves
dromornithids, which are similar - weakly or non-hooked bill, but large head
and powerful bite - and possibly related. Whenever we find dromornithid
remains they are associated with abundant gastroliths, which (as far as I'm
aware, please correct me if you know different!) indicate predominant
herbivory. What is known of gastroliths in Gastornis? (And if nobody has
published on it, how can people have missed such an obvious alliterative
title?!)

Googling 'Gastornis gastroliths' doesn't seem to get much, except some DML
posts from 2002 (Steve Wroe suggesting gastroliths do not necessarily
support herbivory for dromornithids, based on presence in some theropods and
plesiosaurs, http://dml.cmnh.org/2002Aug/msg00419.html).

'Diatryma gastroliths', otoh, brings up Oliver Wings' thesis (2004), which I
haven't looked at for a while. Wings p.100 writes "Diatryma, a giant
cursorial bird frequently found in the Geiseltal, had no gastroliths (H.
Haubold, pers. comm. 2003). This is consistent with Diatryma?s supposed
predatory way of life." 
Similar beak to droms, but different food-processing abilities. Interesting!

Also, I learned some stuff about cassowaries on TV last night
(http://www.abc.net.au/tv/guide/netw/200907/programs/DO0613V001D26072009T193
000.htm), such as seeing them swallow surprisingly large fruit, and pass
large quantities of seeds (~2cm diameter, sometimes 'hundreds' at a time...
add water, wait a bit, and instant thicket!), which clearly must inform
thinking about behavior involving gastroliths. Also what they look like with
almost no feathers due to illness. And the long 'killing claw' on the foot
shines like steel, they must spend a good fraction of their time sharpening
it (but are still easily taken down by a small pack of dogs).

-----------------------------------------------
Dr John D. Scanlon, FCD
Riversleigh Fossil Centre, Outback at Isa
riversleigh@outbackatisa.com.au
http://tinyurl.com/f2rby
 
"Get this $%#@* python off me!", said Tom laocoonically.

-----Original Message-----
From: Augusto Haro [mailto:augustoharo@gmail.com] 
Sent: 26 July, 2009 7:39 AM
To: DML
Subject: Re: Phorusrhacids killing large mammals in National Geographic
Channel

Now thinking on what Gastornis (Diatryma) ate. Admitting the lack of
the downcurved tip suggests it would not eat animals wider than its
gape... (for most carnivorous/scanvenger birds eating prey in pieces I
know seem to bear these tips, e.g., raptorial birds, cathartids,
skuas), and the powerful bite was not used aginst hypothetically large
seeds... what if the powerful bite was used to break tree branches in
order to reach fruits/distal leaves? Elephants do so, and it is
difficult to me to find other adaptive explanation (assuming there is
one) for their tusks (ignoring intraspecific combat/sexual selection).
Alternatively, the beak is somewhat shovel-shaped, so what if they
used it to unearth tubercles/small animals. This may require some
force, overall if the adductor musculature is employed in the digging,
and pigs have also strong bites. Anyway, I think powerful jaw muscles
do not only have to suggest hyaena-like bone-cracking. Gorillas and
pandas provide other examples of powerful bites directed against
bamboo.

Regarding the question of whether the downcurved tip of the upper jaw
of phorusrhacids implyied carnivory: are not the most prominent of
these beak tips present in macaws?