REFUTING "PACK HUNTING" (LONG)

[franczak@ntplx.net (Brian Franczak)]

In the latest installment of this seemingly never-ending (but thoroughly
enjoyable if somewhat vitriolic) thread, Chris Campbell wrote:

> It is? I thought it was based on the fact that 20% or so of all
>Tenontosaurus > material is found with Deinonychus teeth. Since
>Tenontosaurus is 4-5 times    > larger than Deinonychus on average, pack
>behavior seems to me a reasonable    > explanation for the association. I
>suppose the relationship could be somewhat > like that between tigers and
>elephants in south Asia, but that seems less     > likely to me.

The original YPM site containing the fragmentary, scattered remains of
three _Deinonychus_ and one ornithopod (it wasn't known at the time that
this was _Tenontosaurus_) were the impetus for Ostrom's assessment of the
material being the result of cooperative hunting. Only since then have
additional sites with tenontosaur remains and shed _Deinonychus_ teeth been
found and that "evidence" added to the pro-"pack hunting" argument. Larry
Dunn made the following point previously, but I'll reiterate: Shed teeth
from multiple dromaeosaurs in association with a single prey animal does
*nothing* to indicate (or prove) "pack hunting" behavior. A *single*
_Deinonychus_ could have taken down a moderate-sized _Tenontosaurus_, had
his fill, and left the carcass, which was then visited over the next few
hours? days? weeks? by a passel of other individual dromaeosaurs. They're
just as likely to shed teeth in this way as any other. More on this
later...

> I think this is very unlikely.  First, the beak was U-shaped, suited for
> cropping vegetation but nowhere nearly as effective as a ceratopian's
> beak might have been in defense.  Further, the tail was stiffened to a
> large extent, making it difficult to use as a weapon.  Yes, it's
> conceivable, as many things get used as weapons in desperation; however,
> I think attacks with the forelimbs (which are very robust) are much more
> likely.

Your original argument was that the tenontosaur was completely without
defense capabilities.

> True.  I'm not sure kicking would be much of an option, though.  It is
> not built like a horse, after all.

Does an animal have to be built like a horse in order to kick? What about stomp?

> No, I imagine it certainly tried to run away.  I imagine they probably
> lived in herds to reduce the chances of being hunted.  I also imagine
> that Deinonychus would likely only try for juveniles, since (as John
> Ostrom pointed out) the fully mature Tenontosaurs were likely too big.
> Mass is effective as a defense, and I think the larger Tenontosaurs
> probably relied on that to some extent, along with herd behavior.

If _Deinonychus_ was hunting juvenile tenonontosaurs, why would it need to
use cooperative hunting to bring down the prey? Size and mass-wise, they
were probably pretty close; an individual _Deinonychus_ could make short
work of a juvenile, particularly if it employed the commonly-ascribed
hunting techniques.

> I think the main problem with this site is that it can't be adequately
> explained no matter what view you take of things.  Let's assume that the
> Deinonychus weren't hunting the Tenontosaur; how, then, did all of them
> die?  There's no reason to think the Tenontosaur killed the dromies; if
> they're not hunting it, that explanation gets tossed.  How, then?  Did
> they kill one another?  That's about as far-fetched as them being
> crunched by the Tenontosaur.  No matter how you look at it, this site is
> weird.

The "pack-hunting" scenario is too far-fetched an explanation for this
site. A more realistic analysis rules this out, even if it doesn't supply
an answer. Speculation is fine, up to a point, but I'm a firm believer that
we need to be a bit more conservative.

> Oh, come on.  What about the various coelurosaurs running around?  The
> ornithomimids?  Other dromaeosaurs?  These groups were active throughout
> the Cretaceous, and members of each group were certainly contemporaries
> of Deinonychus.  Lizards, eggs and mammals would be perfect food for
> members of these groups.

I didn't say that there *weren't* other small predators, only that using
them (since they're virtually unknown) was a bad argument. But
_Deinonychus_ is not a particularly large animal itself; it's not
unreasonable to assume that it fed on small prey when the opportunity arose
as well.

> Let's remember that wolves *do* hunt moose, caribou and bison when they
> can.

But *not all the time*.

> Speaking strictly in ecological terms there's no reason Deinonychus
>wouldn't  > take the largest prey it could safely manage, just as wolves
>do.

Of course _Deinonychus_ would "take the largest prey it could safely
manage". And an *individual* _Deinonychus_ was certainly capable of
catching and killing a juvenile tenontosaur. And I'm sure there were plenty
of other large prey animals in its environment that didn't grossly exceed
its own body mass that would fit this scenario just as well (How about your
"various coelurosaurs, ornithomimids, and other dromaeosaurs"?). If it
could do that, why create the elaborate "pack" scenario?

> I expect it certainly made do with lizards and mammals and eggs and
>whatever  > else it could lay hands on when it had to, just as wolves make
>do with mice
> and berries when they have to.  I see no reason to assume it only
>scavenged    > Tenontosaurus, though, particularly since some 20% of all
>Tenontosaurus finds > have Deinonychus teeth associated with them.
>Nothing is that particular about > meals it *scavenges*.

Neither I nor anyone else ever said it only scavenged tenontosaurs.

> If you would kindly explain the presense of Deinonychus teeth in so many
> Tenontosaurus finds, then, I'd be more likely to dismiss the idea.  What
> we know is this: Deinonychus interacted in numbers of three or greater
> on at least some occasions (whether to fight or hunt or whatever, we
> don't know) and Deinonychus had a taste for Tenontosaurus flesh.

Again, shed teeth do not *prove* predation, only that the animals that shed
the teeth fed on the animal. There is no way to know if they did so
collectively all at once or individually over a period of time. Likewise,
your statement that "Deinonychus interacted in numbers of three or greater
on at least some occasions" is completely unfounded. Associated skeletons
are not necessarily indicative of social interaction, and even so, the
*level* of interaction is not so readily definable. It is usually a mistake
to speak in absolutes this way, particularly about the behavior of extinct
animals and particularly when the evidence for the proposed behavior is
ambiguous.

> We know it is arguably possible that they could physically attack an animal
> larger than themselves, and we know that even such things as spiders can
> hunt cooperatively in some circumstances.  This indicates to me that it's
>> certainly *possible* that Deinonychus hunted Tenontosaurus in packs.
>The       > evidence available does not invalidate this idea, but there's
>not enough of it > to really support anything, IMO.

If you had said this in the beginning, this entire thread would never have
been created. Yes, it's *possible* that Deinonychus hunted Tenontosaurus in
packs, but the evidence to actually support this notion is weak.

> Agreed, but these go both ways.  It seems every therapod is being called
> a scavenger these days, and the notion gets to be too much at times.

All extant predators scavenge, and this would certainly apply to theropods
as well. But I know of no other theropod than _Tyrannosaurus_ being called
an *obligate* scavenger at this point, and AFAIK, only Jack Horner ascribes
to that theory.

> If Tyrannosaurs were scavengers and Deinonychus were scavengers and
> Coelurosaurs and Ornithomimids only went for eggs and small mammals, who
> killed all of these large herbivores?  Someone had to kill them all if
> everyone's scavenging on them, but the main candidates are now
> scavengers!  Maybe they just had the courtesy to die at a set time, thus
> providing a fresh source of carrion for all of our therapods on a
> regular basis.  Awfully nice of them.

Again, I never defined _Deinonychus_ as an obligate scavenger. But the fact
is that the greater majority of extant predatory animals (mammals, birds,
fish, insects, whatever) are *not* cooperative hunters, no matter *how* you
define cooperative. This type of behavior is a rarity, the exception to the
rule. And I think that assigning this specific behavior to dinosaurs is an
iffy proposition at best, particularly when the evidence supporting it is
questionable.

> As is the notion that therapods couldn't have operated in packs, or the
> notion that they couldn't have hunted large animals.  I understand that
> you don't want us to get carried away, that that's fine; there is such a
> thing as going too far, however.

How is it going "too far" to ask for a reasonable assessment of the fossil
data? The only thing that goes "too far" these days is unfounded
speculation based on little or no hard evidence. And since the
extraordinary claim of theropod "pack hunting" is being made, the defense
of that theory rests with its proponents, not the reverse. To date, I do
not think anyone (including Dr. Ostrom) has made a convincing case for such
behavior.

Let's look at the original description of the material. Regarding the
'64-'67 YPM find, Maxwell and Ostrom (JVP Vol. 15, No. 4, 27 Dec. '95) have
this to say on the subject (from the Introduction):

"Ostrom explained the association as evidence that _Deinonychus_ probably
hunted in packs of six, eight or more predators, a group capable of
bringing down much larger prey animals, such as _Tenontosaurus_. That view
has been generally accepted ever since, but not without question. The
taphonomic details of this association, and other new taphonomic  evidence
supporting Ostrom's interpretation, are presented here. The evidence is
circumstantial and could be interpreted in several ways, but the original
portrayal of _Deinonychus_ as gregarious, raptorial killers fits the
evidence most convincingly."

They then go on (still in the Intro) to discuss the more-recent MOR find:

"The most recent discovery of _Tenontosaurus_ remains preserved with shed
_Deinonychus_ teeth ... provides interesting taphonomic data that seem to
support the supposition that _Deinonychus_ engaged in pack-hunting at least
some of the time, as well as possible solitary hunting or scavenging at
other times. The aggressive design of most of the anatomic specializations
reported by Ostrom, however, argue in favor of active predation, rather
than a scavenging way of life for _Deinonychus_. Furthermore, the new
discovery appears to substantiate Ostrom's (1970) conclusion that the
repeated association of _Deinonychus_ and _Tenontosaurus_ remains indicates
a clear food preference on the part of _Deinonychus_."

Under "Yale _Deinonychus_-_Tenontosaurus_ Associations":

"_Tenontosaurus_ is the most common element of the Cloverly fauna and its
remains were collected at 58 different sites in ... 103 localities...
_Deinonychus_ remains were found close to, or intimately associated with,
_Tenontosaurus_ remains at 14 of the 58 sites. _Deinonychus_ material was
found at only six sites that lacked _Tenontosaurus_ remains. It is also
significant that _Deinonychus_ remains were rarely found associated with
any other possible prey taxa, such as the nodosaur _Sauropelta_, which is
the second most common element of the fauna."

So, 14 of 58 sites had remains of both predator and prey. This is less than
one quarter of the sites. This average does not seem particulary
impressive. Factor in the other 6 sites where _Deinonychus_ was found with
*no* prey remains, and it's even less so. And what, exactly, does the
sentence "rarely found associated with any other possible prey taxa" mean?
They don't say *never*, only *rarely*. So, what other prey *has*
_Deinonychus_ been found associated with that we're not being told about?
The phrasing here is deliberately misleading, I think, stacking the
argument in favor of "prefered prey" and "pack hunting".

Discussing the "MOR Specimens", they write:

"The MOR _Tenontosaurus_ skeleton is a sub-adult, measuring approximately
4.5 m long. ... There are 10 maxillary or dentary teeth and one
premaxillary tooth (of _Deinonychus_). No other skeletal elements of
_Deinonychus_ were found at the site."

This, of course, is where the "pack hunting" argument goes south, IMO. How,
precisely, does this site help bolster the "pack hunting" theory? A
*sub-adult* tenontosaur found associated with some shed teeth. Why is a
"pack" necessary to subdue this prey?

On "Taphonomy of _Tenontosaurus_-_Deinonychus_ Sites (Yale Sites), they write:

"The _Tenontosaurus_ fragments show no tooth marks or other direct evidence
of predation or scavenging."

and...

"None of these ... elements ... bore tooth marks that would indicate the
work of scavengers, but tooth marks are rare in dinosaur assemblages."

and...

"The undisturbed caudal tendon alignment, the extremely delicate skull and
jaw bones with no evidence of wear or pre-burial breakage, and the
conspicuous absence of any sorting or current alignment, counter any
suggestion that these remains were transported to the site by water
currents."

The remains, sure. But what about the "pre-remains" bodies of the animals?
The "most persistent facies of the Cloverly Formation ... has commonly been
interpreted as overbank flood deposits and discontinuous river channel
deposits." Rising water couldn't have carried the bodies -- killed
elsewhere under unknown circumstances -- to the site, deposited them,
receded, and then buried them after "...scavenging by small, unrecorded
animals would appear to be the most probable explanation of the scattered
and highly dispersed remains..."?
Am I missing something? If someone can tell me why the scenario I propose
is flat out impossible, I'd certainly appreciate it. (No sarcasm intended
here.)

Regarding the association of the predatory/prey remains, they write:

"It is unlikely that these repeated occurrences are just chance
associations. Scavenging or predation, or both, are the only logical
explanations."

and...

"The most intriguing association ... is that of an uncatalogued skeleton of
_Tenontosaurus_ ... and a single _Deinonychus tooth ... During collection
it was noticed that the mid-section of _Tenontosaurus_ was missing, just as
though bitten away by some predator, but the rest of the skeleton was
intact and in natural articulation ... This _Tenontosaurus_ specimen is
that of a juvenile no more than two meters long ..."

Back to the original YPM site:

"The most important evidence from YPM-64-75 suggests that not fewer than
three _Deinonychus_, and probably five or six more (the successful
attackers), were involved in the attack on at least one medium to large
_Tenontosaurus_. In fact, this _Tenontosaurus_-_Deinonychus_ sample *might*
(italics mine) have been much larger, but quarrying was constrained by a
high precipice of overburden and the limits of the bone-bearing horizon
were never reached. Furthermore, material had also been lost to erosion
before the site had been discovered. The _Tenontosaurus_ remains are
fragmentary, preventing an estimate of its size and weight, but the
_Deinonychus_ remains at the site more than likely represent individuals
killed by the much larger _Tenontosaurus_ defending itself against the
attack."

Please read the above paragraph carefully. It seems to me that there is a
whole lotta supposition going on here. Look at these sentences... "...not
fewer than three _Deinonychus_, and *probably* (italics mine) five or six
more (the successful attackers)..." ... "...quarrying was constrained by a
high precipice of overburden and the limits of the bone-bearing horizon
were never reached..." ... "...material had also been lost to erosion
before the site had been discovered..." ... "..._Tenontosaurus_ remains are
fragmentary, preventing an estimate of its size and weight..." ... The
evidence, weighed judicially, does not corroborate the scenario concocted
to explain the site. Saying that "We might have found more if we could have
dug further" or "Most of the site was washed away before we got there" does
not give credence to the notion that there was more to the site than was
found; claiming otherwise is more an exercise in fantasy than science, IMO.
And what about those "five or six more" _Deinonychus_? Is there actual
evidence for them, or is this just speculation used to bolster the "pack"
idea (since 3 dromaeosaurs are insufficient to the task?) Again, no sarcasm
is intended. Is there evidence for 5 or 6 more _Deinonychus_ at this site?

Later, they write:

"The MOR site yielded 11 _Deinonychus_ teeth, all of which were situated in
the pelvic region, close to the right femur and the humeri, suggesting that
the successful attackers concentrated their feeding in this area. We have
no way of knowing whether the carcass was scavenged after being abandoned
by the predators, but assuming for the moment that it was not, 11 teeth is
still rather too many for three or four _Deinonychus_ to lose while feeding
on the carcass."

Please be aware of the assumption being made above...

And...

"It is possible that the _Tenontosaurus_ (MOR 682) died from some natural
cause other than age, or was killed by only a few _Deinonychus_ (or some
other larger predator as yet undiscovered), and was subsequently scavenged
by many _Deinonychus_, some of which lost teeth while feeding. The problem
with such a scenario is that the MOR _Tenontosaurus_ skeleton is
articulated. Attack and feeding by a large predator should have resulted in
a much more disturbed carcass. Scavenging of a decaying carcass by a large
number of smaller individuals would, in all probability, have disrupted the
main body of the carcass and disarticulated the skull, limb girdles,
vertebral column, and ribs. Only the hindlimbs, forearms, and hands have
been disturbed, and the 90 degree twist in the vertebral column may have
resulted from consumption of the viscera and the flesh around the pelvis
and hindlimbs where all the recovered _Deinonychus_ teeth were situated.
The animal may have died on its belly with the anterior portion of the body
falling on its right side after removal of the abdominal flesh. It seems
most likely that the attackers fed on the freshly killed carcass which was
buried shortly thereafter."

The use of words and phrases like "would, in all probability" and "may
have" and "it seems most likely" is very telling. They are evidence that
even the authors understand the need to hedge their bets about the "proof"
that these sites supposedly supply. They are not incontrovertible evidence
for "pack hunting"; the authors' bias towards that interpretation is
evident, but even they admit that their theory is just one possible
scenario.

They finish with this sentence:

"There is no way to disprove that the carnivores were only scavenging at
both the YPM 64-75 and the MOR CL-103 sites, but it is our opinion that the
evidence, even though circumstantial, supports active predatory behavior
rather than scavenging."

Active predatory behavior, sure. "Pack hunting", not so much...




Brian (franczak@ntplx.net)
http://www.geocities.com/CapeCanaveral/Launchpad/2045/