Re: Some Speculation pt. 1

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>I've been doing some research on a background thread on the
>habits of modern carnivours, trying to get a feel for the
>way dinosaur ecologies may have worked.

[Too bad you weren't on the net a few months ago - if someone saved that
mail thread, you might want to send it to Larrry.]

>But I can't find too many instances of _non_pack hunters
>amongst the living carnivours.  The largest solitary hunter
>I can find is a bear, which is an omnivour, and the largest
>non-omnivour I can think of is the tiger.  Virtually all the
>others are pack hunters to some degree or another.  And even
>tigers have a social life, at least intermittantly, and mates
>have been known to hunt together.

Modern carnivorans are all very bright, as animals go.  I don't know if
thylacines (wolf-like marsupials) were said to have been pack hunters - but
it is true that their brains were smaller than those of canids of equal
mass.

As much as I like theropods (and tyrannosaurids in particular), none of
them had enough brains to have been mental giants by today's standards.
They may have had proportionately larger brains than contemporaneous
herbivores, but nothing like the brain of a lion or wolf.

So, very complex social interactions like lion or wolf pack hunting may
have been beyond T. rex's capablities.  Not to say that some form of group
hunting was possible (crocs and sharks do so with proportionately smaller
brains than a theropod), only that the highly-integrated system of true
modern pack hunters may not have been within a dinosaur's abilities.

>T-rex doesn't _look_ like he needs help.  He's _huge_, he's
>got big teeth, big claws, big muscles - but let's face it,
>he's less than a fifth of the size and weight of even a
>medium-size saurian.

I presume you mean "sauropod".  However, T. rex lived in regions with only
one known sauropod species (Alamosaurus sanjuanensis), and that wasn't a
particularly big one.  T. rex is comparable in mass to the most common
Lancian herbivores, Triceratops (and Diceratops and Torosaurus) and
Edmontosaurus (and Anatotitan).

>I don't suppose it is likely that dinosaur society was identical
>to some modern carnivour, but there must be parallels.  Looking
>at the Nat'l Geo article on lions, I suddenly glimpsed a pack
>of stalking rexes sneaking through the night, one part harrassing
>the saurian herd, another trying to cut one out for a full-scale
>attack.  A saurian, mano-a-mano with a 'rex, would have few
>defenses except sheer mass - the tails seldom seem to have enough
>relative mass or muscle to be real weapons.

Actually, the whiplash tails of diplodocids and the club-tails of some
Asian sauropods might make excellent weapons.

> Big
>and mean-looking as they are, I'm not so sure a t-rex can move
>_that_ fast,

A lot of evidence is suggesting that 10 m/s is well within tyrannosaurid
speed capablities.  That's better than most of us can do!

>nor dish out damage _that_ quickly to something much
>larger than itself.  It also seems to me that such a hunter would
>have needed arms to help latch onto and hold the prey, so as to
>increase the "dwell" time and thus increase the probability of
>inflicting a lethal bite.

I REALLY hope someone saved my carnivore predatory technique posting, so
they can send him the appropriate part of the message.  ;-)

>This seems more plausible for an allo-
>saur, and better for smaller prey - and the tiger, even though
>bigger than most lions, does specialize in prey not much larger
>than itself, and usually much smaller.  As do wolves hunting
>alone.
>
>_But_ - if the 'rex was backed up with a pack, then the retreating
>saurian would be in a world of trouble as other members of the
>pack bored in from the side or headed it off.  A saurian surrounded
>by 'rexes would be a goner, but still a dangerous adversary because
>of the mass and because, if panicked (and I surely would be if I
>were surrounded by a hunting pack of t-rexes) it might lunge
>through and break the line, possibly trampling one or more of the
>rexes (possibly breaking a leg?).  The same thing can seen today
>with lions hunting elephants and cape buffalo.  It is now less
>important to physically grapple the prey - just head it off and
>keep it from turning away from the bites.  Interestingly, wolves
>show much the same behavior when pack hunting - they use no claw
>attacks at all, just the bite, and they, too, tackle very large
>prey, relatively speaking.  Similarly the hyena.

Okay, you don't need that part of the posting...

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.