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Horner & T. rex
>> I was fortunate enough to go to the dedication of
>>the T-rex in UC Berkeley today. The guest lecturer was John Horner.
Just hoping I get invited as a guest speaker at a hadro function sometime :-(
>and discuss several dino issues. Just for fun I showed each of them a
>tooth I found in Montana this summer and asked them to identify it. A
>grad student (supposedly a tooth expert) said definitely Albertosaurid,
>possibly Daspletasaur. Another Horner grad student had said the same.
>Padian declined to venture a guess. Horner was positive it was a Dromaesaurid
Just a note: Horner is a hadrosaur specialist. Having some pretty good
ideas as to who the Berkeley and U Montana grads are, I'd go with their
>I took notes during Horner's "T.rex as scavenger" talk; his points are
>summarized below. I am still unconvinced, but I now have a much better
>appreciation for that viewpoint. His arguments are:
> - Predators *need* arms to catch prey.
> T.rex arms are too small, with too limited movement to be used
> to catch prey.
Tell that to wolves, Lycaon pictus, and phorusrachids!
> - 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.)
Smaller tyrannosaurids have shins which are longer than their thighs. No
other >4 tonne animal has as long a shin relative to thigh as Tyrannosaurus.
> - Predators need good vision, therefore large eyes.
> T.rex had comparatively small eyes, and small optic lobe.
It has not been demonstrated that tyrannosaurid eyes are too small.
Relative eye size decreases faster than overall body size: compare the eyes
of foxes to wolves, small cats to tigers, Hyracotherium to Equus, etc.
> - T.rex had unusually large olfactory lobe; implies especially
> acute sense of smell. Only 2 other animals in history ever had a
> proportionally larger olfactory lobe: kiwi and turkey vulture,
> one of which is a scavenger.
And one of which is an omnivore, so what does it all mean? Furthermore,
when was the last survey of the relative size of the olfactory lobes in
dinosaurs: the 1920s?
> - T.rex teeth are often found among mono-specific bone bed sites;
> implies T.rex was scavenging the mass deaths in herbivore herds.
So what? Dromaeosaurid teeth are also found there. Almost no predator
(except for some snakes, perhaps) will pass up a chance to scavenge.
>These are good arguments, but I believe there are good rebuttals to each.
>Certainly T.rex scavenged opportunistically, but I still don't buy Horner's
>scavenger-only idea. I did challenge Jack on a couple of points:
>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.
Ummm, no. Albertosaurus, Daspletosaurus, and other basal tyrannosaurids do
not show the well developed potential for stereoscopic vision.
>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".
Isn't this a Lancian bone? If so, what other predator could there have been
of that size in the U.S. during the latest Maastrichtian?
>Still, he made a reasonable case even though he is not as serious about it
>as he seems. In "The Complete T.rex" Horner admits that he is not sure
>about the scavenger theory, but he often talks that way when talking to
>others, just to take up a contrary position.
Thomas R. Holtz, Jr.
Dept. of Geology
University of Maryland
College Park, MD 20742