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Triceratops, assualt, and battery
There have been quite a lot of posts on this since I last checked in.
I am not a ceratopsian expert, but I will try to address a few things
from several people:
Betty Cunningham said:
"Dinosaurs having no patella means a single sharp direct implement
at the knee could dislocate the lower leg."
Oooo .... careful, careful! To compensate for no patella, I already
told you that dinos extend their cnemial crests, but there is also a
deep groove that the quadruceps tendon slides in, and the groove has
high walls: slipping out of the groove is pretty hard. Plus, unlike
mammals, the tendon doesn't wrap up and over the knee as much as it
inserts in more of a bee-line fashion onto the cnemial crest. But I'm
glad you liked my last response. =)
Brian "Philidor" said:
"Does this help indicate the angle at which the front legs of
held? If the leg is not straight and directly under the animal but
and at an angle, as I've seen it drawn, would all the weight of the
put on a muscle or something else rather than straight onto the bone?
seems like it could be painful as the animal got older."
As Andy Farke pointed out, Rolf Johnson and John Ostrom published a
paper in 1995 in which Rolf and co. assembled a life-sized cast of a
Torosaurus forelimb. Rolf attached large bands to all the major
muscle scars to help restore the natural position of the forelimb as
best as possible.
Even without worrying about muscle attachments, there is no way to
make the forelimbs go together so that the elbows point back without
either dislocating the radius bone in the forearm or rotating the
manus (hand) so that it faces backwards! In other words, the
forelimbs of ceratopsians appear to be bent, with the elbows sticking
out to the sides.
The humerus of ceratopsians is very robust, and could probably take a
bit of tensile stress (bending stress) without harm. The olecranon
process on the ulna (the "elbow" that you point to in your own arm, a
place where an extensor muscle called the Triceps attaches) is very
well developed, and you tend to see large olecranon processes in
animals that have bent limbs: check out the situation in non-dinosaurs
like Dimetrodon and other synapsids or the dinosaurs Stegosaurus and
Ankylosaurus which may have also had a bent forearm.
Having a wide gait may help support a big head, as was mentioned here
before I'm sure. The weight is still being supported by the arm and
foot bones, but not in strict compression: this would help explain the
thickened humerus of ceratopsians. Bird femora are held more
horizontally than extinct theropods, and because their femora
experience more bending stress, they have become thicker as well.
Finally, as Andy Farke notes, Tyrannosaurs may not be good
side-steppers. The femoral head of most dinosaurs was not
spherical-shaped like in mammals, but was instead cyclindrical,
meaning the hindlimbs could move back and forth easily but had limited
side to side motion. Furthermore, the pubes and ischia, the pelvic
bones on which adductor muscles (muscles which pull the legs in toward
the pelvis) originate, are rather small in most dinosaurs (as they are
in many mammals, but remember those spherical femoral heads). These
muscles would assist in side-stepping, and the reduced pubis and
ischium suggests that pulling the limbs in toward the body was not all
that common in dinosaurs.
Whew! Are you tired of me too?
Dept. Biological Sciences
Northern Illinois University