Re: your mail

[Jeffrey Martz <martz@holly.ColoState.EDU>]

Resonses and questions concerning Achut Reddy's posting:

>       - Predators *need* arms to catch prey.
>         T.rex arms are too small, with too limited movement to be used
>         to catch prey.

     Crocodilians don't.  Neither does the Secretary bird. For that matter, 
neither do dogs.  If those big Tertiary ground birds were predators, 
they didn't either.  Of course, this raises the question 
as to exactly how the jaws and teeth functioned if T.rex was a predator.  
I think Horner has a point in T.rex leaving all its teeth if it tried to 
hang on to the Triceratops and drag it down like mammalian predators.  Of 
course, crocodiles do something similar.  How strongly rooted were T.rex 
teeth?  
     Would Mr. Paul please reiterate his "cookie cutter" argument on 
theropod teeth?  What other ideas are out there for how theropod teeth 
functioned?
  
>       - Fast runners have long shin bones compared to thigh bones.
>         T.rex has shin, thigh bones of equal length, so it must have
>         been a walker (conflicts somewhat with his book, where he allows
>         for the possibility of a 25 mph T.rex.)  

     An animal with a mongo stride like T.rex could move pretty quickly, 
running or not.  Now that the "galloping ceratopsians" 
(ceratopians, whatever) has been largely shot in the head, catching up 
with a Triceratops couldn't have been too difficult for an animal as leggy 
as T.rex.  
     What sort of speed estimates are out there for non-galloping 
Triceratops and Torosaurus?  What about duckbills?  

     I have to admit the arguments concerning eyesight and smell are 
compelling.  
     Are there ANY big predatory animals that use smell over sight? 
How good was tyrannosaur hearing?

>       - T.rex teeth are often found among mono-specific bone bed sites;
>         implies T.rex was scavenging the mass deaths in herbivore herds.

     Not many predators will turn down free food if its availible.  One 
question I have about big scavenging theropods is:
     Would they encounter dead meat OFTEN enough to keep fed?  Obviously, 
if a T.rex runs into a dead Triceratops or Anatotitan, to say nothing for 
an Allosaurus and a sauropod, its going to eat good.  But how long 
between meals?  It is fine if if finds food, but will it starve to 
death before it finds another carcass?  There is a finite amount of meat 
it can store in its belly.  What sorts of mortality rates might there be for 
big herbiverous dinosaurs?
     I have heard two contradictory arguments for T.rex predation based 
on modern carnivores:
     1.  Modern carnivores get most of thier food from hunting.  The only 
total scavengers are flying birds that can cover a wide area very quickly. 
(I think this was one of Mr. Paul's).
     2.  Modern carnivores mostly scavenge (I think this was one of Mr. 
Horner's).
     Comments?  
   
> 1. I asked why T.rex would need stereo vision if it only scavenged.
>    He said stereo vision is a primitive feature that T.rex just inherited,
>    although it has no need for it.

     I read somewhere that stereoscopic vision is not necessarily 
inferred by forward facing eyes.  What sorts of animals have forward 
facing eyes that don't have stereo?  I also thought that 
tyrannosaurs had eyes that were more oriented forward than earlier 
theropods.  What sort of ancestors was this primitive condition derived from?
 
> 2. I asked how he would explain the recent find where T.rex tooth mark
>    was found in a herbivore bone that had healed over, implying the
>    dinosaur had escaped and survived a T.rex attack.  His answer was,
>    "it's not a T.rex tooth mark".

     Are you referring to the Denver Museum of Natural History 
Edmontosurus tail?  The new mount that it is in has the tail held about 8 
feet off the ground, right around mouth level for a T.rex.  The wound 
consists of a (very) roughly semicircular shape in the neural spines 
about 10 inches (?) wide and 6 inches (?) deep, where the neural spines 
are either broken off and partially healed over, or at least mangled.  
There is a spot on one spine where a hole has been punched clean 
through.  
     I've looked at it, but I don't know much.  Ken and Jerry have 
examined more thoroughly and might have more to say on the subject.    

J.Martz