Re: Lack of Running Giant Theropod Tracksâ

[Augusto Haro <augustoharo@gmail.com>]

I will follow this deathmatch scenario mostly as a nice speculation
exercise, because as far as I know, there is no much evidence of this
particular confrontation in the fossil record (e.g., not evidence of
Tyrannosaurus bones broken by Triceratops horns, or Triceratops killed
by Tryannosaurus instead of merely consumed), and there is evidence of
theropods mainly focusing on juveniles, in a recent paper by Hone and
Rauhut. Indeed, I now think preying upon juveniles is a great strategy
for carnivorous dinosaurs not only because of facing likely slower,
less defended prey, but also because dinosaurs grew too fast, and put
such a large number of eggs (compared to the descent of ungulates),
that the supply of juveniles may have been much greater than that of
adults, which need too many years to be replaced (and where grow is
slowed). This is for the sake of sustainability of the system,
necessary for the predator, which would otherwise more likely
extinguish its prey, and then become extinct after, if focusing on
large prey. Something similar explains why the wood production is
difficult to made sustainable, because trees take such a long time to
grow that sustainable rate of collection quotas would be too small.

2010/12/10 Sim Koning <simkoning@msn.com>:
>
>>If it took the chest, good. But the torso is short and the legs wouldmove 
>>fast in the worried >predator, so it would not be easy to miss thelegs. In 
>>addition, the target is relatively small if >catchedfrontally.
>
> I think it's worth noting that the head of a Triceratops is rather wedge 
> shaped, which would reduce the likelihood of a straight on collision.
>
That also means that the snout is transversally narrow, which coupled
with the large size of the nares would make the snout more fragile if
hitted by, say, a fastly protracting knee.
>
> The snout may not have been as weak as it seemed on the dinosaur documentary. 
> I still maintain that the "experiment" was limited and rather flawed. For the 
> sake of argument, I'll give it the benefit of the doubt however. I don't 
> think the nasal horn would work as a 'primary weapon', but I imagine it would 
> do some minor damage if it contacted flesh during a struggle. I'm guessing 
> every little bit would help in a life and death struggle with a 6 ton 
> super-predator.

Well, the enlargement of the nares seems like pretty weakening to me.
I remember your former argument that the neck is more flexible than a
pole, but even when this is true, ceratopsians also present many
cervicals fused, so their neck was not be as flexible as most
ornithischian necks.
>
>>On the other hand, I was yesterday reading that the antelope whichbetter 
>>defends itself from >dhole packs is one with short horns. Thissuggests to me 
>>that relatively short horns are better >when dealingwith predators because 
>>they permit more maneuvrability at close range.
>
> Yes, but a T.rex was a far less maneuverable predator with much greater 
> 'firepower'. A single bite from a Tyrannosaurus rex may been crippling or 
> fatal.

I do not know. Proportionally, dholes are one of the carnivore species
with a more powerful bite, and I would bet their bite was stronger
than in the theropod, even if Tyrannosaurus was the strongest biting
theropod. In any case, loss of maneuvrability is also present in the
ceratopsians, so the conditions would be even with respect to
maneuvrability in both duels (both dholes and serows are likely more
maneuvrable). I can see that being on four legs makes you more stable,
but do not know if any more maneuvrable (perhaps because the force of
more limbs can be used against the inertia in the moment of turning?).
However, large birds as rheas commonly engage in rapid turns to fool
quadrupedal predators. Perhaps stronger hindlimbs, with the
recognition of a huge M. caudifemoralis longus, as seem to be the
massive ones of Tyrannosaurus, may compensate for greater
maneuvrability.

>Perhaps longer horns that could penetrate the heart and/or lungs with a single 
>blow would have been more useful.
>
I do not know how wide the chest of Tyrannosaurus was, however, or if
the relationships are any less comparable than between dhole and
serow. One can also make the claim a gazelle can more likely kill the
African wild dog, if it hits the point, than a short-horned serow when
stabbing the dhole... However, this does not seem to be the case.
Perhaps the large size and rotation inertia of a long horn also makes
it slower to move if not charging. To me, a charging animal, as those
with long horns, seems to depend much in easily to predict runs.
Cretan acrobats seemed to fool bulls, as do dogs with gazelles.
Animals better for fighting in close contact, if able to avoid such
charges, have a huge advantage. It seems to me that may be why
gazelles and and most antelopes better try to run. May the
proportionally longer hindlimbs of Tyrannosaurus give it some edge in
velocity to avoid charges?

>>it is posited that both the frilland horns are more likely of use in 
>>intraspecific contest than >fordefense. The frill is also full of superficial 
>>vessels (with apossible thermorregulatory >function), >and some bite directed 
>>at it mayimply dangerous blood loss.
>
> I very much agree that this was one of their primary functions, if not the 
> primary function, but this does not mean that they could not have been very 
> effective weapons for self defense too. We Humans use our legs primarily for 
> locomotion, but they can also make for extremely effective weapons for self 
> defense.
>
In the case of the frills, some of these present large hollows.
Additionally, the blood loss because of the number of blood vessels
seems to be weakening...

>>I said it may be, but phylogenetic bracketing on living forms providesyou the 
>>more parsimonious >hypotheses on the basis of the current evidence. More 
>>parsimonious does not imply more certain. >Many birds hunt animals, not only 
>>raptors, and in most of them no collective organization is >seen. Carnivorous 
>>dinosaurs may have hunted in groups,or not - the last being more parsimonious 
>>>to infer. That they can befound in close association may indicate 
>>gregariousness(orpreservational >bias), as in crocs and many birds, not 
>>necessarilycooperative hunting.
>
>  I think since we now have rather strong evidence that some theropods 
> employed some behavior that was staggeringly similar to some modern birds 
> (such as nesting strategies) we are justified in speculating that many 
> theropods may have had a similar degree of sociality.

I acknowledge many archosaurs, birds and crocs, are gregarious, and
this may well be a basal archosaurian condition -I actually do not
know-. What is to me not supported by these relatives is the presence
of pack hunting. Mongooses are carnivorous mammals which can be very
social, perhaps with societies as complex as in canids, but do not
engage in pack-hunting (they can pack-mob larger predators as jackals
or eagles, however).

> However I feel it's just as important to understand why it is various bird 
> species are social, and some are not, before we start applying bird behavior 
> to dinosaurs (for the sake of life restoration). For instance, we may not see 
> many pack hunting birds of prey, but this may be due to a limited food supply 
> and the need for relatively large hunting territories.
>
But, a similar or even larger food supply would be necessary for
larger pack-hunting ground-based mammals, as African wild dogs or
lions. This does not stop them. Birds may even save energy by looking
farther from their high viewpoints, or catch air currents, instead of
dwelling around in the search of what to eat.

>>one crocodile, manyend up biting it and thus collaborate in killing it in 
>>practice, butit does >not imply that the intention was to rely in 
>>othercrocodilians, and may just be a case of intended >unique 
>>predationcoinciding with the attempts of other crocs - perhaps the origin 
>>ofcooperative >hunting and cognitive association of these occasions 
>>withsuccess in killing by the individual >predators?).
>
> Good point, I didn't think about that. Of course we do have modern caimans 
> and birds forming creches, and we now see this behavior recorded in dinosaur 
> fossils, so using phylogenetic bracketing to infer behavior certainly has 
> some merit. I also remember seeing alligators working together to form a 
> living fish trap somewhere...
>
Ok., but creches are not pack hunting. I read about crocs making fish
traps, but individually.

>>Your example of the bats indicates the dangers of inferring from theRecent 
>>only. But, in lack of >more conclusive evidence either way,parsimony is all 
>>you have.
>
> I think it depends on what behavior we are talking about. Many once thought 
> it was more parsimonious to apply scales to small dinosaurs, which ignored 
> the probability that they were likely warm-blooded animals, and that mammals 
> have hair that evolved for insulation, so dinosaurs may have done the same.
>
Well, in reality filling dinosaurs with scales is not more
parsimonious than putting protofeathers in them because now you have a
basal state being featherless (crocs, lizards, etc.) and a derived
state with feathers (birds). As birds seemingly come from dinosaurs,
it is equally parsimonious in principle putting or not feathers on
them, because you have to make a similar number of assumptions -either
feathers appeared on the ancestor of pterosaurs+dinosaurs or just in
birds). Now, not only parsimony is not opposed to birds being
feathered; we have actual evidence of these feathers (we have also
evidence of scales, nonetheless, so different dinosaurs or body parts
had different epidermal covering). I admit that, although with the
argument of endothermy instead of evidence or parsimony, Bakker hitted
the nail in the seventies.
>
> I could make the same argument in regards to social hunting: we don't see 
> birds of prey hunting in packs, but they are flying animals, and predatory 
> dinosaurs may have filled niches more analogous to modern predatory mammals, 
> and so may have had analogous behavioral adaptations.

How analogous they were is difficult to assess. They seem to have
relied heavily on young, stuff smaller than themselves. In this they
resemble predatory birds, perhaps the lifestyle proposed for
phorusrhacids. Although toothed, they are rather fragile because of
all their pneumaticity, as are birds. And, proportionally and
generally speaking, their bite forces are much lower than in mammalian
carnivores, as in birds. And their grasping capabilities are lesser
than in most carnivores (just as most birds which are not raptorial).

Other thing, I think pack hunting is rare in most mammalian
carnivores, excepting some (but never all) canids, lion, spotted
hyena, and some otters (I forgot, although not Carnivora, it is also
present in chimps). It is also rare in flying predatory birds, so this
may not represent a not much weirder thing in predators of the air
than in those based on land. I suppose birds of prey may conceivably
gain too much by hunting like wolves, perhaps being able to kill
larger prey than they do and being more able to defend the kill from
scanvengers and even mammalian carnivores (however, if they can't
defend, there you may have an argument against them hunting grupally).

I personally think a good analog for theropod hunting lifestyles is
some kind of weakly jawed unsocial canid which goes around hunting
stuff smaller than itself, more or less like a bat-eared fox without
hunting insects.

>>In any case, it seems that theropods mostly ate young, as many Recent 
>>predators, and thus would >not have requiredgrupal hunting.
>
> This could also mean that the young may have engaged in group hunting as 
> well. Heck, as I suggested with T. rex, for all we know the young may have 
> been pack hunters, while the breeding adults may have been solitary or 
> monogamous. This would be an intermediate between the creche forming of crocs 
> and other dinosaurs, and the monogamous behavior of most modern birds.
>
On the basis of parsimony I would not favour the hypothesis that the
youngs were pack hunters. Besides parsimony, it seems to me like
difficult to infer, even if you consider wolves and lions, I do not
know if there is something on their bony skeleton which indicates them
to be grupal hunters, for large cats and even some populations of
wolves have solitary habits with much the same anatomy. You may need
perhaps evidence of the same individual being bitten by many different
individuals, but then, if the bites were responsible of killing it, I
do not know how to differentiate it from scanvenging. I do not know,
not even smartness may be a parameter, for there is no much evidence
of lions being more brainy than tigers, or dholes and African wild
dogs than wolves (not so social) and those than foxes. As far as I
know, we do not have evidence of whether or not Panthera atrox and
Smilodon were or not pack hunters. And the same may be said for most
fossil hyenas, for only a hyena species hunts in packs (I will not be
as bold as saying the same applies to Canis dirus; this species may be
better studied).
>
>>Whether the adult ceratopsians did or did not put mucheffort in the defense 
>>of their youngs is >unknown.
>
> There was the Psitticosaurus that was found dead with a creche though.
>
Ok., but something is to be found caring for the young and other to be
engaged to death against a predator in their defense. If the predator
is too dangerous, at some time many mothers leave.
>
>  Triceratops was the most abundant herbivore in a Tyrannosaurus's ecosystem, 
> and we have evidence of an actual battle between the two species; I would say 
> the chances are pretty good that they attacked and killed Triceratops quite 
> often. Many pack hunting predators will grip the head/face of their prey 
> while others go after the throat of guts. The bitten off horn on the 
> Triceratops may be evidence of very similar behavior among T. rex.
>
I am not aware of evidence of that battle. There is a bitten pelvis,
and then you mention a bitten off horn, but this may also conceivably
reflect scanvenging (of which Tyrannosaurus may have also made use).
In my viewpoint, killing juveniles is more supported by evidence and
seems more logical for the own sustainability in time of the
populations of Tyrannosaurus. I think even juveniles may have hunted
juveniles of other dinos. And this is compatible with either
cooperative or non-cooperative hunting.
>
> Simeon Koning