Mr. Bouyer

Day 1 | Day 2 | Lab | Reading Assignment

Describe the characteristics of the Class Mammalia. Compare the types of teeth in mammals. Read and write dental formulas. Compare monotremes, marsupials, and eutherians. Use a dichotomous key to identify Texas mammal Orders.

Animal Identification Assignment.

What's special about the 28 teeth of an armadillo?

The Texas Longhorn, , is the Texas State "animal".

Class characteristics:

Hair
Mammary glands
Heart is 4-chambered
Breathing diaphragm
Viviparous
Endothermic

The opossum, Didelphis virginiana, is the only marsupial in the northern hemisphere. Marsupials give birth to tiny, embryonic offspring that complete development while attached to a nipple in an external "pouch" on the abdomen of the female.

All other Texas mammals are eutherians, placental mammals. The placenta develops from embryonic cells that grow out from tissue surrounding the developing embryo and make contact with the uterine wall. Placental blood vessels absorb nutrients from the mother's body by osmosis, but there is no direct connection between the circulatory system of the embryo and the mother.

The shrew has the distinction of being the only poisonous mammal in North America. While it doesn't have fangs, its saliva has a toxin that paralizes its prey. Shrews are very aggressive and will attack animals several times their size. If shrews were not the smallest mammals in the world, they would be the most feared.

Texas has 22 species of bats, the only mammals that can fly.

For sheer numbers, the Mexican freetail bat, Tadaria mexicana, is the most common. There is a colony of these bats in Texas that numbers well over a million individuals. Bats have a weight to surface area ratio that allows them to actually fly. The front legs of bats are modified into wings. Most of the wing surface area comes from a hairless membrane covering the fingers of the hand. The bones of the bat skeleton are not hollow or porous, but they are very small and lightweight.

Mammal teeth:

The teeth of mammals are highly specialized for their specific diet. Mammals are heterodont, meaning that they have several types of teeth.

Most mammals have 4 types of teeth:
Incisors - teeth with a single cutting edge.
Canines - round teeth for puncturing.
Premolars - teeth with several cutting edges for shredding.
Molars - teeth with a flat surface for grinding.

Mammal teeth are thecodont, being set in sockets in the jaw bones.

Most mammals are diphyodont, having two sets of teeth. They first grow a set of deciduous teeth, which are shed and replaced by permanent teeth as the jaws grow to full size. These "milk teeth" do not include molars. The permanent teeth of many mammals stop growing when they reach full size. These teeth are called rooted teeth. The teeth in some mammals continue to grow throughout life. The incisors of rodents are examples of these rootless teeth.

Dental Formulas:

Mammals can be identified by their dental formula, which is an expression of the number of each type of tooth on one side of the upper jaw over the number of each type of tooth on one side of the lower jaw.

In-Class Assignment 161:
This assignment must be turned in by the end of class totoday to receive credit.
Scoring criteria

1. Humans are known to be omnivores, equipped to feed on all types of food. What is the best equipped omnivore on the table?
2. Which animal on the table is a pure carnivore?
3. What's with the armadillo?
4. How many teeth are in the skull of a dog?
5. What type of teeth grow throughout the life of the organism?
6. What tooth type is not found in deciduous teeth?
7. What mammal found in Texas is poisonous?
8. What bones make up most of the wing of a bat?
9. How do the shapes of premolars and molars different?
10. Canine teeth are for puncturing. Why does a carnivore need puncturing teeth?

Day 2

What two things make the skull of an opossum very easy to recognize?

Mammal classification:

There are less than 950 species of living mammals contained in 16 orders:

3 species of monotremes
57 species of marsupials
the remainder are eutherians

The skulls of mammals are quite distinct and can be used to identify the species of the animal. The drawings below shows the top and bottom of a mammal skull with parts labeled.

Details of skull top

Details of skull bottom

Tracking:

Mammals usually leave distinctive tracks the can be used to identify the animal and determine a good deal of information about it.

Raccoon	Coyote	Deer	Mouse	Skunk

Portfolio Assignment 162:
Scoring criteria

1. What is the pronounced ridge running down the top center of some mammal skulls called?
2. There is a hole at the back of a skull through which the spinal nerves connect to the brain. What is this hole called?
3. Why are size and color not generally used for mammal identification?
4. Use this mammal key to answer these questions:
   1. What bone do marsupials have that is found in no other mammal?
   2. Mammals that have no hind limbs are found in what orders?
   3. Number six on the key refers to "feet unguligrade". What does that mean?
   4. Do rabbits have canine teeth?
   5. The bony ring around the eyes of primates is formed by what two bones joining?
   6. How are the feet of deer and horses different?
   7. The killer whale is a meat-eater. Why is it not classified in the Order Carnivora?
   8. What is the distinguishing characteristic of the Order Chiroptera?
   9. What Oklahoma mammal has homodont teeth?

Research Links:

• Class Mammalia - U.C. Berkeley
• Short-tailed Shrew - Illinois Natural History Survey
• Eastern Mole - Illinois Natural History Survey

Zoology Class

All the teeth of an armadillo are the same type.

The brain case of the opossum is extremely small compared to the overall size of the skull. The opossum has 50 teeth, the most of any mammal in Texas.