High fibre diet (was "Re: And the T. Rex bell goes "dung"!...")

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 04:20 AM 6/19/98 -0400, Laurine Nyveen wrote:
>Here's a thought that only 4 a.m. can inspire:
>
>1) Tyrannosaurs excreted crushed bones
>2) Up to the the discovery of the recent coprolite, pretty much every
>researcher felt that tyrannosaurs used their mouths primarily to carve out
>and swallow chunks of soft tissue.
>3) Some surprise has been expressed concerning a tyrannosaur using its
>teeth to finely process bone.
>
>Here's the idea:
>
>Tyrannosaurs did carve out huge chunks of meat, and bone.  It didn't crush
>the bone with its teeth.  Why?  Because it had gastroliths to do that.
>
>Has anyone ever looked for gastroliths associated with large theropods?
>Heck, it might even be a primitive trait shared with theropod/sauropod
>ancestors.

(Actually, since both crocs & birds use gastroliths, it's probably a
primitive archosaurian trait).

>Has anyone seen the paper yet?  Can the bones' fracture morphology reveal
>what sort of forces crushed them - i.e. pounding with rounded surfaces or
>high pressure tooth edge piercing?

>From the paper:
"The pronounced fragmentation and angularity of the consumed bone indicate
that it was fractured before ingestion - apparently by biting during
feeding.  Although extant birds (avian dinosaurs) often use a horny gizzard
and/or ingested grit for food maceration, such mechanisms could not have
been solely responsible for the degree of comminution seen in the coprolite.
Furthermore, significant tituration would have resulted in well rounded bone
clasts, and there is no evidence for the use of gastroliths by non-avian
theropods"

(That last statement, though, ignores the phylogenetic evidence, and indeed
(as reported in National Geographic) some of the new Chinese theropods have
gastroliths).

>I doubt the bones would have many revealing marks left after passage
>through the GI tract, but Tom, if you figger this out, Andrew Hill will be
>so proud.  :)

Indeed!  Unfortunately, Chin & company already done the analysis, so all I
can do is report it (and modify my talk on skull mechanics of tyrannosaurids
for SVP...).

Speculation time!:
As the authors point out, there has been very little evidence for large
scale bone modification (i.e., bone cracking or crunching) by theropods
based on in situ finds (mostly the work of Tony Fiorillo).  At best there
are tooth scrapes, some puncture marks (as in Erickson et al.'s own work on
T. rex bite forces), but nothing like the cracked bones found in mammal
fossil and modern sites.

So, most of us had concluded that theropods either a) ignored the hard parts
while feed, except for scraping the bones clean or b) did the crocodile
method: rip of a big chunk of animal, and swallow it whole (bones and all).
These methods still might be the way that most big theropods fed, pending
discovery of allosaur or abelisaur or what have you coprolites.

This tyrant turd, though, suggests that tyrannosaurids at least occasionally
munched up their food before swallowing.  (They couldn't "chew", in the
sense of tooth-tooth grinding, because their jaws didn't work that way.
Like most toothed theropods, tyrannosaurids had a pronounced overbite: all
the dentary teeth fit inside the upper teeth).  With their incrassate
(inflated, thick) teeth and big ossified secondary palates, tyrant dinos
would be the best adapted of all large theropods to crunch down on their
food a couple of times before swallowing.

It should be pointed out that Chin et al. have determined (from bone
histology) that the food item in this case was a subadult ornithischian
dinosaur, from somewhere between 200-750 kg weight (based on the presumed
diameters of the long bone material).  Perhaps the tyrant was able to get
some pretty big portions of the herbivore into the mouth and mashed it
before swallowing.  It might not have been able to do this with the big
bones of an adult Triceratops or Edmontosaurus, and that might be why
Fiorillo and others haven't found heavily modified large dinosaur bones.  It
may be that tyrannosaurids only started to process their food this way after
they had the chunk all the way in their mouth, so only coprolitic material
(rather than in situ long bones) would show such modification.

Just some initial speculations.

The paper also discusses the amount of digestion of the bone fragments, but
I'll wait until others get to read about this find before talking about that.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661