[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Re: re:Dinosaur Hunting techniques



>> Tyrannosaurus does not LOOK very gracile, for two reasons:  1) at such a
>> large size, gracile limb proportions look bulky.  However, compare the
>> hindlimb of Tyrannosaurus with an elephant, a rhino, a Triceratops, even an
>> Edmontosaurus.  You will see that the T. rex legs are more slender and have
>> relatively longer tibiae and metatarsi.  2) The most famous T. rex mount in
>> the world, AMNH 5027, has the wrong legs!! Since this specimen (a gracile
>> morph) lacked hindlimbs, Osborn et al. added casts of the legs of the type
>> (now at the Carnegie).  The type is the robust morph, and a larger
>> individual!
>
>Ok. So let me get this straight.  Somebody attatched the wrong legs?  
>Also, I thought that T-rex had been sort of classified a slow poke because 
>it's thigh bone (sorry, I don't know the correct term) was too short when 
>coupled with the lower leg.


Okay, there are two problems here.  The first is that the "classic" T. rex
mount (AMNH 5027) has legs too bulky for that particular individual.  Second
is the thought that, because T. rex had a femur slightly longer than the
tibia, it had to be slow.  However, in both absolute and relative terms, the
lower leg in tyrannosaurids is much longer and more gracile than any other
large dinosaur (and most any multiton mammal, with giraffes, giraffe-mimic
camelids, and indricotheres being the only exceptions I can recall off hand).
>
>> Dromaeosaurids have about the least gracile limb proportions of any nonavian
>> theropod (only therizinosauroids had worse!). Crichton aside, dromaeosaurids
>> were probably not very fast runners relative to tyrannosaurids,
>> ornithomimids, etc.  Instead, they were probably cat-like ambush predators,
>> relying on short bursts of high speed, quick turns, and an all-out attack
>> with all four legs and the mouth, too!
>
>Deinonychus is still my favorite Dino and the Chetah is my favorite 
>almost cat.  Your description of how a Dromaesaurid might have hunted 
>sounds a alot like a chetah.  Would a cladist now clasify deinonychus 
>as the grand father of the cheatah?  Sorry.  I got carried away.

Yes, you did, but my description is NOT that of a cheetah.  Cheetahs are
dog-mimicing felids, with claws without the high degree of curvature,
blade-like profile, and retractiblity of other felids.  Leopards, jaguars,
pumas, lions, and tigers are all much better analogs for the raptors.

>> Actually, cheetah tails are held about as rigid as they can be, except at
>> the base.  Cheetah's and other big cats use their tails as dynamic
>> stabilizers, to turn on a dime at high speed.  This is exactly the condition
>> we find in the Dromaeosauridae.
>
>If I remember correctly a chetah can reach 70 mph and sustain that speed 
>for about 20 to 30 seconds.  I've always understood that they actualy
dislocate
>their shoulders.  I don't recall reading anything that tells me dinosaurs 
>came anywhere close to this speed, so I would'nt expect to see an adaptation.
>Why the rigid tail?  Was the tail more for balance in turns only or could
>it be a speed adaptation?

Crichton and Speilburg both have Velociraptor running at cheetah speeds:
most unlikely.

Cheetahs attain their high speeds by vertebral flexion: when they take off,
they strech their bodies out as far as they can, increasing their stride
length.  Since theropods were bipeds with fairly stiff backs, they could not
use vertebral flexion to increase their speed.

The exteme rigidity of the tails of dromaeosaurids are much like those of
some pterosaurs (and Archaeopteryx), and were almost certainly more involved
with turns at high speeds.
>
>I hope I didn't loose your point Tom.  If I understood, you said 
>that "relative" to T-rex the dramaesauridae were slower.  So if I had one 
>of each animal, both 16" long, the T-rex would win the speed contest?

To put it on equal terms, if you have a 500 kg dromaeosaurid (such as
Utahraptor) and a 500 kg tyrannosaurid (such as Alectrosaurus), the tyrant
dinosaur would be faster.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084