Lab #3: Crocodiles - Chris K & Cait F

Friday, February 3rd

This lab was really fundamental in understanding reptile skeletal structure and skull morphology. The focus of this blog will primarily be to point out the names of these bones and structures as we learned them in class; they give a good foundation for learning the structures of other reptiles!

The Skull

Besides the diapsid condition, the skull (aka the cranial skeleton) demonstrates other important structures for classifying crocodiles; namely by their mandibular symphasis, ectopterygoid, anterior process length, and the equality of anterior surangular margin length.

The length of the snout is a very tell-tale sign of what kind of croc you have. Right are the skulls of: Caimaninae, Alligatorinae, and Gavialidae

The Skeleton

In lab we observed the complete skeleton of a Crocodilian. Things we looked at include the vertebral column, girdle, limbs and rib structure. Some other essential structures are demonstrated in the diagram below.

Reproduction

These reptiles are similar to the reptiles from previous labs because they are amniotes that internally fertilize and directly develop the cleidoic egg (which in this case is pliable). The reproductive differences crocodiles exhibit is much more parental care, different morphology of the male copulatory organ, and a non-laterally oriented cloaca. Shown is the antero-posterior cloaca from which the "penis" of crocodiles emerges when mating.


Diversity

Unfortunately, a lot of species of Crocs are endangered due to habitat destruction, harvesting for food/skin, and for safety reasons in recreational areas.

The diversity of Crocodilians includes 3 Superfamilies which are Gavialidae, Alligatoridae and Crocodylidae. Among these 3 Superfamiles there have been 23 species described but there is still debate about the exact phylogeny of Crocodilians.

Gavialidae
These crocodilians prefer fast flowing rivers and specialize in eating fish. They are also the most aquatic of the superfamilies.

Alligatoridae
This is the only superfamily that we saw in lab. Alligatoridae have broad jaws and all teeth are held inside a closed mouth. The specimens we observed in lab were identified as Caiman.

Crocodylidae
This superfamily has a long narrow snout compared to the Alligatoridae. The 4th mandibular tooth lies outside of a closed mouth.