Reptiles A. Cladistics 1. Many groups of organisms are “polyphyletic” a. This means that the group combines 2 or more lineages - example=fish 2. Cladistics follows only pure lineages going back in time - example Osteichthys B. Reptile Classifiecation - looks like a polyphyletic group 1. Dry skin - no loss of water through skin like amphibians 2. Aminotic egg - an egg that can survive on dry land - in contrast with the amphibian egg C. Mammals and Birds are derived from different lineages of reptiles (We will see below) D. Stem Reptiles 1. Different lineages based on the temporal region of their skulls - number of holes (or bars) a. These holes are necessary to accommodate large jaw muscles b. Anapsid Skull - no holes in temporal - jaws can move fast, but with little force 1. Muscles that move the jaw are small 2. There is no good paleotological evidence for the transition between amphibians and reptiles - no fossil intermediates a. Fossil amphibians have lots of dermal bones in skull b. Amphibians have no temporal openings in skull 1. (Aside) both fossil amphibians and primitive reptiles have a parietal “eye” that senses light and dark (“third” eye in middle of head) c. Reptile skull is higher than amphibian to accomodate larger jaw muscles d. Of the modern reptiles only turtles are anapsids 2. Diapsid Skull - has holes in the temporal region a. Diapsid reptiles gave rise to lizards and snakes - they have a diapsid skull 1. Also Tuatara, crocodiles, dinosaurs and pterydactyls Reptiles b. One group of diapsids also had a pre-orbital hole in the skull in front of eye - this hole is still preserved in the birds - this anatomy suggests strongly that the birds are derived from the diapsid reptiles 3. Diapsid lineage a. On the way to the dinosaurs b. Occipital condyl - where the skull attaches to the spinal column 1. Single in all reptiles including synapsids 2. 2 in mammals c. Modern reptiles 1. Snakes a. Highly modified jaw - really movable b. Allows snake to eat large prey 3. Synapsid Skull a. Only one hole in temporal region of head b. No synapsid reptiles survive today, all are fossils - mammals have modified the synapsid skull 1. Strong evidence that the mammals are derived from the synapsid reptiles c. Comparison with humans - Temporal opening still in same location as in synapsid reptiles 1. Still have a boney arch through which the temporalis muscle passes a. You can feel the boney arch, it is your cheek bone b. If you touch your temporal region on both sides of your head and clench your jaws you can feel the temporalis muscle tense up - that is right at the location of the temporal opening in the skull Reptiles d. Comparsions between humans and synapsids are tough because the synapsid reptiles had long muzzles like modern dogs 1. Humans have a face that is pushed in without a muzzle E. Amniote Egg 1. Amphibian egg is buried in jelly - absolutely needs to be in water 2. Poses a problem for a land-dwelling organism - “holds them back” 3. Fully adapted land-dweller needs an egg that will not dry out, will have enough food to carry the embryo to term, needs to be porous enough to let in air to breath a. Big engineering problem - solved by reptiles, birds and mammals b. Most of the egg is yolk (the food for the embryo) c. The embryo develops as a little disc on the surface of an enormous yolk d. Cleavage division on surface of yolk e. Blastopore on one side of this embryonic disk f. As it develops - the embryo grows around and envelops the enormous wad of yolk g. Amniotic folds grow over the embryo and form a water-filled amniotic sac 1. Substitute for the water in which the amphbian ancestor laid its egg 2. The amniotic sac is still present in mammals a. When a pregnant woman’s “water breaks”, the amniotic sac is breaking just before the baby is born - it releases the water in which the fetus developed h. Alantoic sac 1. Outside of amnionic sac - it is the location of gas exchange 1. O2 in CO2 out i. These membranes solve the problem of dessication j. Egg shell a. Placed around the egg before it is laid b. Needs to let gases through but not water F. Modern Reptile Types 1. Turtles Reptiles a. Drived directly from anapsids b. Ribs are incorporated into shell - they don’t move separately like they do in all other vertebrates 1. Different from all other tetrapods 2. Scapula is under shell and so are limbs - ribs are outside limbs! 1. Shell seems to grow over the scapula and limbs 2. Lizards a. High diversity b. Snake-like tongue in the Varanid (monitor) lizards 3. Snakes a. A few primitive snakes have limb remnants - male pythons have claws! 1. No front legs at all in snakes 4. Dinosaurs a. Brachiosaurs and Tyrannosaurs b. Pteradactyls 1. Membrane flight - no feathers 2. Related to dinosaur line 3. Many got pretty large - up to 25 ft 4. Tremendously modified head .