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RE: Gastroliths (Theropods)

To: dinosaur@usc.edu
From: Ben Creisler (bh480@scn.org)
Subject: RE: Gastroliths (Theropods)

The recent thread on dinosaur gastroliths mentioned a couple
of coelurosaurs (an ornithomimid and an oviraptorosaur) that
were found with "stomach stones." Although the received wisdom
has long been that carnosaurs, if not nearly all other theropods,
lacked gastroliths, a couple of reported examples deserve mention.

The recently described Lourinhanosaurus antunesi Mateus, 1998
(Mateus, O. 1998. Lourinhanosaurus antunesi, a new Upper Jurassic
Allosauroid (Dinosauria: Theropoda) from Lourinha (Portugal).
Memorias da Academia de Ciencias de Lisboa. 37: 111-124) was
found in association with apparent gastroliths. Here's a quote from
page 119:

"The specimen had 32 gastroliths and the enveloping sediment
preserved the negative imprint of 3 additional gastroliths. The
maximum observed gastrolith length is 22 millimetres. Near the
pebbles there were three small bone fragments that seem to be
food remains. The gastroliths have been found in the rib cage
below the eleventh dorsal vertebra. The high number, concentration
and relative size of the gastroliths suggest that they belong to
this specimen, and that they had not been swallowed when
eating other dinosaur's stomach."

The skeleton is incomplete (lacking any part of the skull)
and is missing the part of the pubis that would show if it had
a "boot." The author concludes, though, that Lourinhanosaurus
was an allosauroid (possibly a sinraptorid) based mainly on details
of the pelvis and hindlimb elements. He also states that "This
is the first non-avian theropod found in association with gastroliths."

This statement is not strictly accurate, however.

Eudes-Deslongchamps (1838) described a group of between
8 to 10 rounded pebbles found under the ribs of Poekilopleuron,
the biggest being around the size of "a large nut." Based on the
discovery of similar stones in the skeletons of marine crocodiles
from the quarries in the same region of Normandy, Eudes-Deslongchamps
concluded that the stones were in the animal's stomach. He also
identified a fish tooth and what appeared to be partially digested
fragments of a "cartilaginous fish" among the pebbles, apparently
belonging to the squalid genus Cestracion. He was surprised, however,
that more of the fish's many pavement-like teeth were not found
with the gastroliths if indeed the fish remains came from Poekilopleuron's
last meal. Owen later used the presence of gastroliths to argue, along
with other grounds, that Poekilopleuron (which he spelled Poikilopleuron)
was a crocodile rather than a dinosaur.

These two examples at least raise that possibility that some large
meat-eating theropods may have had gastroliths.  It could be argued
that some ornithomimids,  oviraptorosaurs and therizinosaurs may
have had gastroliths to help break down plant material that was
part of their diets, but why any large carnosaurs might have had
gastroliths is less clear.  Clearly, any study of gastrolith function in
dinosaurs needs to address the issue, or at least refute the apparent
association of gastroliths with both of these specimens.