allosaur sabertooths(?)

[longrich@alumni.princeton.edu]

On Wednesday, August 7, 2002, at 07:05 PM, Colin McHenry wrote:

> Scott wrote
> > Actually, I was refering to the functional analysis of muscle 
> > insertation
> movement within a phylogenetic context.  Not enough of those, although 
> I'd
> like to see people other than just Bob tackle the subject.  I won't 
> disagree
> with any of your points on tooth shape from a functional point of 
> view.  I
> would like to caution that adaptation does not always reach an optimum.

	I think the thing is that Bakker's argument is contingent on 
demonstrating that allosaurids were optimized for a saber-tooth style 
attack. If you take away the optimality part you take away his argument.
	Animals can do things they aren't specialized for, of course. But 
to infer that behavior from morphology one needs to do something like 
demonstrate that they are specialized for that behavior, and Bakker 
hasn't done this for allosaurids in my opinion. If anything they seem 
among the most poorly designed theropods out there in terms of a 
saber-tooth attack, the teeth are shorter and stouter than just about 
anything else which contrasts with mammalian sabertooths. Of course, we 
don't really know for sure what mammalian saber-tooths were doing 
either. If I recall the old idea is that the lower jaw just swung out of 
the way, but I think there is some recent work suggesting that the lower 
jaw was used to drive the canines in, particularly around the throat. 
They are dead however which makes them frustrating to use as analogues, 
though.
	As for the idea that the teeth function together as a sort of 
continuous cutting surface this make sense. Presumably sharks and komodo 
dragons are doing something like this, or steak knives for example. 
There is a paleolithic technology called microblades where small flint 
blades are arranged on a wood or bone implement to create a continuous 
cutting surface, this presumably provided the sharp edge of flint with 
the toughness of wood and bone- large stone tools being really brittle. 
The Aztecs took this technology to the maximum with their weapons, I 
think they are called macuahatl or something- heavy wooden clubs with 
long obsidian blades arranged on their edges to create a continuous 
cutting surface; there is supposed to be an account of a Spaniard having 
his horse's whole front leg chopped off by one of these in one of the 
few battles against the Aztec empire. And you might be tempted to think 
sleeper sharks (Somniosus pacificus) are not particularly ferocious due 
to their very short teeth, however these suckers are capable of gouging 
out huge chunks of flesh. Looking at a halibut which has been attacked 
by a sleeper shark, it looks as if a giant ice cream scoop nine inches 
in diameter has been used to carve out a huge sorta hemispherical chunk 
of several pounds of muscle. As you might have guessed, these bigass, 
black, luminescent-green-eyed dogfish are related to the cookie-cutter 
sharks. I think the upper and lower rows of teeth are different here, I 
forget which is which but one row has pointed holding teeth and the 
other has low, wide, rectangular, almost incisor-like teeth arranged in 
a nearly continuous cutting surface.
	So yeah, just because allosaurids had short teeth we can't discount 
them as dealing out some serious damage... presumably they weren't the 
most abundant predators in the Morrison without being able to take down 
a fair chunk of the biomass. On the other hand I think it sort of 
complicates if not wrecks the argument that they were working like 
Smilodon et al. Presumably the primary cutting surface in _Smilodon_ is 
the posterior edge of each canine, perpendicular to the long axis of the 
skull, in Allosaurus it would be the continuous row of teeth, parallel 
to the long axis of the skull.


By the way, I really liked Bakker's paper.  I love the left-field stuff.
> Better to be wrong than dull, as S.J. used to say. ( Someone once said 
> of my
> grandfather that, of ten ideas he'd put forward seven would be 
> impossible -
> but of the other three, one would be a winner.  What do think, Darren?  
> Runs
> in the family?)

Someone once said that the way to double your success rate was, double 
your failure rate. I think this is important, science isn't about coming 
up with the right answer the first time around but a process of sorting 
through all the wrong answers. I think Bakker got a a lot wrong but he 
also came up with more interesting ideas and did more to spur people on 
than many people who got it right most of the time but never really went 
out on a limb. On the other hand there are some people like Darwin who 
were able to combine real creativity and impeccable argumentation. 
_Origin_ remains one of the best books out there on natural selection 
which is astonishing when you consider how little he had to go on. He 
was just damn curious, damn honest, and damn meticulous.