Re: Triceratops defence

["Matthew BONNAN" <Z966341@wpo.cso.niu.edu>]

Betty:

You said: "Could a ceratopian or hadrosaur or other herbivourous
dinsoaur be
ham-strung?  That is, do they also have the large tendon of the leg
exposed near the knee as do large mammals?"

Well, all tetrapods have "hamstrings," which are the muscles on the
posterior side of the thigh (femur) that help flex the leg and
partially extend the femur.  I think you might mean the gastrocnemius
muscle, which is the large "calf" muscle on the posterior surface of
your leg.  It originates on the proximal end of the tibia (in some
tetrapods, portions of the muscle bellies of the gastrocnemius are
seen in anterior view) and combines with the soleus and plantaris
muscles to form the calcaneal or "Achilles" tendon.  In mammals, the
"Achilles" tendon inserts on the calcaneal tuberosity and when these
muscles contract, the foot (pes) plantarflexes (the toes point down,
the heel moves up) and helps to push the leg off the ground during
locomotion.

In dinosaurs, a calcaneal tuberosity is not developed and the ankle
is hinge-like.  Instead, in reptiles (and in birds with some
differences), the "Achilles" tendon inserts onto a tough tissue on the
sole and "heal" of the foot (pes) called the plantar apneurosis.  The
plantar apneurosis acts like the calcaneal tuber in mammals and helps
give the gastrocnemius muscle a better angle of insertion on the foot.
 Something like this was probably present in Triceratops, though to
what degree is difficult to tell because the plantar apneurosis does
not leave muscle scars.

In addition, the knee of all known dinosaurs (at least that I've seen
and am aware of) did not have a patella to assist the quadruceps
muscles inserting onto the tibia.  To compensate for this "loss of
leverage," dinosaurs and other reptiles have developed a larger
cnemial crest to keep a decent lever advantage for these leg-extending
muscles.  The cnemial crest is sometimes called the tibial tuberosity,
and it is located just under the proximal portion of the tibia.

In birds, we many times find at least cartilaginous patellae in the
knee, but in 'gators and crocs we usually don't find any sort of
sesamoids.  There is "roughened" tissue (sometimes called
fibrovessicular) in the knee and elbow regions of 'gators and crocs
that may act like patellae or sesamoids, but we don't find ossified
kneecaps.

Hope this helps?

Matt Bonnan
Dept. Biological Sciences
Northern Illinois University