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RE Richard W Travsky -Bones and stomach acid
(Rescued from truncation)
Thanks, Peter, for this fascinating information.
In a message dated 8/18/2010 5:14:12 P.M. Eastern Daylight Time,
As the past Superintendent of Reptiles at the Bronx Zoo, NY, and a
crocodilian specialist, I've observed the feeding habits of many species of
crocodilian in captivity and the wild. The phenomenon of occurring
crocodilian gastroliths is of particular interest. However, relative to
consumption of prey/food-bones, perhaps I can offer the following
In captivity, modern crocodilians are sometimes fed food items such as
pigeons with feathers, whole chickens, chicken body parts with bone
included, whole white rats and mice, whole fish such as mackerel, trout,
halibut head parts that may include the bones that form the gills. In some
cases, beef meat with cut rib bones several inches long may be fed. What
be most germane is the question of what do ingested large mammal bones look
like after being processed by the animal? Obviously, any resulting fecal
material is easily observed under captive conditions.
However, bones, stones, metal objects, and other ingested none-food items
may be held in the stomach as gastrolithic materials for long periods of
time. Such items may not pass out of the stomach through the small pyloric
valve/opening into the small intestine. Balls of hair the size of beans
from ingested rats may collect and totally fill the stomach. Thick rib
bones may also remain in the stomach. Such items are not passed out as
fecal material but are regularly regurgitated in-mass. It is not unusual
for animal care staff to find the crocodilian pool water surface totally
covered with small pelleted balls of regurgitated rat hair, nor is it
unusual to find the ingested thick beef bones, minus any flesh, on the
bottom of the pool the animals are housed in.
Simply put, when the mass of hair balls, bones, and items that are too
or not digestible but cannot pass out of the stomach - fill the stomach to
capacity, the stomach is emptied by regurgitation. Crocodilian scats or
fecal material does not contain large grit, bone fragments, nor any
appreciable amounts of hair if at all. Also, coins that are thrown into
pool by the public are regularly found in numbers, trapped in the stomach.
Digestible materials may include from observation: soft tissue, small thin
bones, cartilaginous materials appear to fall into this category.
Actual crocodilian stools may be wet and loose, but most often are found as
an elongated, intestine-formed, semi-solid amount of dark gray, fine-silted
In examining stomach contents of wild crocodilians such as Yacare caiman in
the Brazilian Pantanal, that may feed on large aquatic snails, one finds
the snails shell in the stomach, but the snail's operculum, in great
quantities. The operculum being retained from each snail consumed.
Likewise, the long bones, beaks from birds, and the skin of the feet,
complete with toe claws, appearing as a skin glove, absent the legs inside,
may be found in the pools of captive animals - presumably regurgitated
with hair balls or the center quill-vane from feathers, but not the feather
filaments. Thus looking at fossil crocodilian food-bones in terms of
scats may be inappropriate as they in fact may be regurgitations.
I published a short paper on the occurrence of gastroliths in modern
crocodilians and I am happy to provide a copy if anyone wishes it
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