The characters that unite ornithiscians, primitively they have leaf shaped teeth. This is teh tooth.
It looks like teh laef of a tree. They way they work is that the upper ones and lower ones come
down next to each other, and slide against each other. They also have a pone at the tip ofthe new
called a predentary bone. The cleft chin is hte remnant of the embryological fusion of our lower
jaw. We have one lower jaw. Reptiles retain for the most part either no fusion at all or a sutural
contact. The bones are strongly held together but they don’t fuse. What these ornthiscians do, the
predentary bone holds the bones of the jaw together. It allows them to flex but it holsd them to
together. They’ll be imparting a lot offorce on the lower jaw through chewing. They also have
the retroverted pubis. It opens up the guts for more intentistines. If you’re an herbivore, you need
al onger intentine to hold it for longer time and give more time for breaking down cellulose.
Another thing that ornthiscian dinosaurs have are ossified tendons. Can anyone tell me what a
tendon is? It is a form of connected tissue. They connect muscle to bones. Ligament connect
muscles to muscles. For example, your Achilles tendon connects your heel to your calf muscles.
If your snap it, your foot with dangle. These naimls had ossified tendons. They allow momvenet.
If you ossify them, they can become actual support structures. Tis is the tail. The vertical bars are
the backbone. Each vertebrate has one.
The ornithiscians diversify...there are some in the Triassic, more in the Jurassic, but in the
certaceous they really take off. They’re dominant in the northern content.
Heterodontosaurus is one of the first ornithisicians. It had well developed teeth that formed a
continuous cutting surface. One thing all ornithiscians have...te teeth are set into the jaw relative
to the lung. These animals had cheeks too. The cheeks are for chewing. They’re muscular.
Cheeks help us manipulate and move food around the oral cavity. These little animals were
sexually dimorphic. Sexual dimorphism is...di means two, morph means form. They had two
forms. They had a male anatomy and a female anatomy. Many many species of animals are
sexually dimorphic. We are dimorphic. We have males and females. Some have tusks, while
others don’t. The tusks were used by males to fight for partners.
The two main groups of hte ornithisicans are the ones you must remember: stegosaurus beloned
to agorup called thyreophora. This is characterized by te evolution of osteoderm.
Osteoderm...osteo-derm. Osteo means bone, derm means skin. Bone-skin. This is the formation
of bony plates within the dermus of the skin. Alligators and crocodiles also have this. What is the
advantage of having bones in your skin? It is for defence against carnivorous dinosaurs. What we
seein these guys is that they start off at the top where the. We find the progressive evolution of
graeter and greater armoured defences. We see progressive quadrapedal. The stegosaurus had
very big hind limbs and very tiny forelimbs.
Stegosaurs are an interseitn group. They’re not good chewer. Tehy have weak teeth, but
spectacular armour. They had plates running down their backs. What were these plates for? They’re thin and bony. What could they be used for? It could be defence but it could also be
thermal regulation or display. The plates are very thin, so they’re not effective armour. They’re
thin and delicate. They could be for thermal regulation. Elephants have big trunks and big floppy
elephant ears. Is it for hearing? It’s thermal regulation. Elephants are huge. They spend their
lives trying to get rid of body heat. The bigger you are, teh more volume you have relative to
your skin. For every doubling of your surface area, your volume increases. Elephants are all
about staying cool. They’re naked. That helps them lose heat. The big floppy ears are radiators.
The plates on stegosaurs perhaps served the same functions. This is not a good idea though.
These animals cannot control the plates. Elephants can control their ears. Well, maybe they’re
for display? How many people here spend a lot of money on their hair? Disp