Specialized Teeth, Endothermy, & Hair Mammals: Specialized Teeth, Endothermy, & Hair

Speculations… Mammals began to evolve about 70 mya during the Tertiary period. The first mammals were small (less than 10cm.) and were nocturnal They probably looked like little rodents. Early mammals were thought to have avoided competing with dinosaurs by feeding on insects at night.

Characteristics Hair – for camouflage and preventative heat loss Mammary glands Specialized teeth Three middle ear bones

Major Orders… Monotremes – egg laying mammals; viviparous (eggs develop inside) Marsupials – pouched mammals Placentals – mammals that carry their babies in a uterus, nourished through the placenta, and give birth to live young Ex. primates

Other Important Orders Ungulates – Hoofed animals Artiodactyla – even-toed hoofed animals (horses) Cetacia – whales and porpoises Some have baleen Chiroptera – bats Lagomorphs – rabbits Pinnepidia – seals and walruses

Teeth Mammals are called heterodonts because they have teeth specialized for different functions. Incisors – used for biting and/or gnawing Canines – used for tearing meat Premolars – used for chewing Molars – used for grinding and chewing Mammals have 2 sets of teeth in their lifetime: deciduous teeth and permanent teeth

Vertebral Divisions in Mammals Unlike birds, our vertebral column is NOT fused Divided into Cervical – neck bones; first two are the atlas & the axis Thoracic – ribs are attached Lumbar – lower back

Circulation Mammals have a 4-chambered heart, separating the two atria from the two ventricles. Remember, veins return blood TO the heart, arteries take blood away FROM the heart to the rest of the body; Pulmonary vessels carry blood to and from the lungs.

Nutrition & Digestion Most mammals (including us) currently have, or have had in the past, a cecum; a fermentation pouch full of microorganisms used to digest tough plant matter. In humans, the cecum has become the appendix. Some mammals (cows) have chambered stomachs. These chambers are called rumen.

Gas Exchange Mammals are the only animals with a diaphragm, which prompts to enter the lungs. Instead of air sacs, mammals have alveoli to increase surface area.

Nervous System The size of mammalian brains is considerably large due the increased size of the cerebrum. Cerebrum allows for more intricate motor, sensory, and intellectual function.