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Re: SVPCA 50, REPORT IV




On Thursday, September 26, 2002, at 03:27 AM, darren.naish@port.ac.uk wrote:


Hopefully this'll be the last email from on SVPCA.
THEROPODS

Paul Barrett showed that Norell et al's recent claim of filter-
feeding and the presence of laminae in ornithomimids was,
err, somewhat questionable (which makes you wonder how
this paper got into _Nature_). In fact the pillar-like vertical
structures seen on the median surface of the ornithomimid
rostrum are pretty much identical to the same structures
seen in sea turtles and ornithischians and are more to do
with the presence of rhamphothecae than anything else
(Nick Longrich and I were already onto this.. Paul has
beaten us to it). Paul also investigated the energetics of
filter-feeding and showed that it would not have been
ecologically possible for ornithomimids to survive this way,
even given a variety of postulated metabolic regimes. More
likely (rediscovery of GSP 1988), ornithomimids were
herbivores.
Aw, nuts. Yeah, I have some cool photos of vertical ridges in the palate of green turtles (which eat a lot of sea grass if I recall). Anyways for other reasons the filter feeding hypothesis doesn't work too well. An obvious problem is that filter feeders tend to have large jaws, since you need a lot of surface area to process for your prey. Examples include whales, basking sharks, megamouth sharks, anchovies, ducks, flamingoes, and Pterodaustro. Ornithomimids, in contrast, are real pinheads, such that it would be very difficult to process enough water to feed them, I suspect. Another is foot proportions. Wading birds like ibises, herons, cranes, and flamingos have long toes to keep them from sinking in the mud. Ornithomimids have among the smallest toes among theropods, suggesting that they were instead highly terrestrial and cursorial, like ostriches and ungulates. Finally there are the forelimbs which have been aptly compared to sloths by Osborn, the long straight humerus, proportions of the manual digits, isodactyly, shapes of the claws all look like them. The knuckles and opposable first digit don't, but they do look like the knuckles of humans and other primates. If these are designed for grasping branches, its hard to figure what could be going on except that they are hooking branches to get at the leaves.