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scapulae, sauropods



Scapulocoracoids:
        The thing about free scapula-coracoid articulations is that the
scapula and coracoid appear to have fused over ontogeny. There is
dromaeosaur material in which the scapula is not fused to the coracoid, and
there is also dromaeosaur material in which it is. Caudipteryx and
Microvenator have free coracoids, those of the Ingenia and an unnamed AMNH
oviraptorid are fused. So what does it mean that Rahonavis and Unenlagia
don't have coracoids fused onto their scapulae? Not necessarily anything.
Incidentally Mononykus does not have a scapula fused to the coracoid. A lot
of characters are like this, you have to look at how they change over the
life of the animal- especially fusion and ossification characters. My guess
is that an adult oviraptorid would have uncinate processes, sternal plates,
a tarsometatarsus, a fourth trochanter, a fused semilunate, and a
scapulacoracoid, but that a hatchling wouldn't have any of these. So we
have to be careful.

Sauropods:
Re: rearing sauropods: I'll agree that it needs to be tested but I must
confess a hunch/prejudice that rearing in sauropods was something that
primitively (e.g. shunosaurus, Jobaria) they were probably pretty good at,
and that various lineages (Camarasaurus, Brachiosaurus) got worse, while
others got better (Diplodocus, Barosaurus, maybe Dicraeosaurus) only to get
worse again (Apatosaurus).
        The important thing about elephants is "proof of concept" rather
than using them as direct mechanical analogues. And in those ways in which
elephants do differ, they tend to be inferior to sauropods- they lack a
heavy tail to serve as a counterbalance, the forelimbs are thicker than the
hindlimbs, they lack the tall sacral "withers" that improve the ability to
support weight from the hips. The rearing hypothesis is testable, of
course. One way is to do some biomechanical modelling; I don't know how
much tweaking it would take to get DinoMorph to do caudals, but you might
expect specialized rearers to have tails that don't have a lot of
dorsoflexion.
        Re: being able to support many times the body's weight, I think
Matt hit the nail on the head with safety factors. As to the
caudofemoralis: wouldn't you expect it to be particularly large in rearing
sauropods? I mean, you've got to derive the lifting power from somewhere:
maybe the femora stay more or less vertical and the CFL retracts, pulling
the tail down towards the ground and the front of the animal up towards the
trees? I don't know how CFLs compare generally, except that in the
diplodocids, which seem most suited for rearing, they are, to use a
technical anatomical term, @^#%&^ing huge, if the massive platelike
transverse processes tell us anything about the muscles inserting there.
How about insertion points? Do diplodocids differ in their insertion?
        I don't have any problem with many sauropods being ground feeders-
mammoths got huge and they weren't cropping trees up in that tundra. A
principle I like to invoke here is the Abraham Lincoln Principle.
Supposedly when he was asked how long a man's legs should be, he said that
"a man's legs should be long enough to reach the ground," or, in our case,
a low-feeder's neck should be long enough to reach the ground. It shouldn't
be too short (although it *can* be in high feeders- e.g. the giraffe, which
has to spread its forelimbs to reach down), and it shouldn't be too long.
This is an admittedly anecdotal way of looking at the world, but the
various solutions to ground feeding that animals have adopted do, I think,
tell us something about which solutions are viable and which are not. What
it looks like to me is that vacuum-cleaner style feeding isn't optimal,
because very few if any animals do that. The necks tend to be, in line with
the Abraham Lincoln Principle, long enough to reach the ground. Gazelles,
horses, duckbills and ostriches have long, erect legs, and tend to have
longer necks. Things like iguanas, pareisaurs and edaphosaurs have short,
sprawled limbs, and have very short necks because they don't have so far to
reach. Camarasaurus, as an example, seems to have a neck that is long
enough to reach the ground, but not substantially longer, so it may have
fed more extensively on ground cover (e.g. ferns) than did the diplodocids.

        I'll agree that what we need is an in-depth biomechanical study. As
for Nigersaurus, I don't even want to try to think about what it might have
been doing.

-nl