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Colleagues,
The ongoing topic of whether
tyrannosaurids were predators or a scavengers (or both) recently came up here at
Tyrrell. Given the rapidity of consumption of prey animals on the African plain,
it is fair to suppose that most "carrion" there is still fresh as many
of the Zebra/Wildebeest and smaller-sized animals are consumed by
primary/secondary carnivores and scavengers within hours of death. So a
scavenger in these instances is still eating relatively fresh meat. But what of
the carcasses of larger animals like Elephants? They cannot be eaten to the bare
bones before their flesh goes "bad", yet animals still scavenge their
putrified carcasses.
There was some discussion on the nutritional value of
rotting/rotten meat and scavenging generally, which brought up some unresolved
questions:
1. Nutritional value of rotting/rotted meat vs. fresh
meat? Anyone have any thoughts on this? Have any studies been done on this
issue? I'd be interested in getting copies of such papers if they exist. Someone
here suggested that the rotting/rotted meat would be more nutritious due to the
secondary ingestion of insect eggs, larvae (maggots), and adult insects. Another
person thought rotten meat was more protein-rich but could not substantiate this
claim.
2. Why scavenge rotting meat anyway? 1. Lack of
available prey? 2. Easier to digest? 3. More "tasty"? 4. Injured
predator cannot catch and attack more "normal" prey? 5. Easier to
"catch"?
#'s 1, 4 and 5 are self evident, but what about #2? Any
other reasons missed here?
3. Near as we could tell, vultures are the only extant
true scavenger. But is this really so? If a hungry vulture was standing around
and an insect or small animal happened by would it ignore this potential meal
completely? Are any vultures known to take live prey? If so, then they
cannot be considered pure scavengers. Maybe there really is no such thing as a
"pure predator" or "pure scavenger"? (but see #6
below).
4. If given the choice would fresh or rotten meat be
preferred?
5. An interesting observation that was pointed out is
that Black Bears generally kill and eat their vertebrate prey (then bury
leftovers for later) whereas Grizzly Bears tend to kill, then bury their prey
and wait for it to "ripen" before returning to feed. Anyone have any
thoughts on why this is so?
6. Are there any pure predators in the world today? I've
personally seen Weasels and Red-Tailed Hawks "catching",
"killing" and eating Richardson's Ground Squirrels that had just
previously (5-10 minutes) been killed by rifle fire. I've also seen several
raptor species eating roadkill. I once read on a bird chat-group where
apparently an Osprey (which is reputed to to be a pure predator) had learned to
regularly steal smoked Herring hanging out to dry. As kids me and my friends
would catch and keep Frogs in pails. My friends "pets" aways died as
they just threw in dead insects for the Frog to eat. Because the insects would
not move, the Frog would not see it and thereby starve. I'd put insects on the
end of a long bristle snapped out of a corn broom and twirl the impaled insect
in front of the Frog's nose and never had any problems feeding them in that way.
Would this movement-related feeding activity make Frog's pure predators? If so,
this would make a Frog more of a "pure predator" than a
Hawk!
Personally I think tyrannosaurids were both predators
and scavengers, but leaning more towards the predator mode. Phil Currie has
co-authored a paper with me on face-biting behavior in some large and small
theropods including tyrannosaurids. This paper is coming out in an upcoming
issue (this year I hope!) of the journal GAIA. This issue is dedicated to
theropod paleobiology. We have healing bite marks on the heads of
tyrannosaurids- 43% specimens in Tyrrell are so affected. Clearly they used
their teeth on each other when alive- so why not use the same teeth on the more
fragile head of a meal- say a hadrosaur? We also have a specimen I mentioned on
this chat group months ago that shows scavenging of a very rotten tyrannosaur
carcass; probably scavenged by another tyrannosaur-- but, that's another
story........ :)
Darren
Darren Tanke, Tech. I
Dinosaur Research Program, Royal Tyrrell Museum of Paleontology, Drumheller, AB, Canada and Senior Editor, Paleopathology and Recent Dento-Osteopathology Bibliography; see homepage at: http://dns.magtech.ab.ca/dtanke |