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Biology
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2. 32-1 Introduction to the Mammals
Photo Credit: ©Zefa (RM)/M. Botzek/Masterfile
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Mammals
All mammals have two notable features: hair and mammary glands.
In females, mammary glands produce milk to nourish the young.
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Mammals
In addition to having hair and the ability to nourish their young with milk, all mammals
breathe air.
have four-chambered hearts.
are endotherms that generate their body heat internally.
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The first true mammals appeared during the late Triassic Period, about 220 million years ago.
These mammals were very small and probably nocturnal.
Evolution of Mammals
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6. Reptile / Mammal Skulls
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7. Form and Function in Mammals
As mammals evolved, the form and function of their jaws and teeth became adapted to eat foods other than insects.
The joint between the skull and lower jaw allowed mammals to evolve larger, more powerful jaw muscles and different ways of chewing.
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8. Form and Function in Mammals
Jaws and Teeth of Mammals
Carnivore
Herbivore
Canines
The specialized jaws and teeth of mammals are adapted for different diets. Carnivorous mammals use sharp canines and incisors to grip and slice flesh from their prey. Their jaws usually move up and down as they chew. Herbivorous mammals use flat-edged incisors to grasp and tear vegetation, and flattened molars to grind the food. Their jaws generally move from side to side.
Jaw joint
Jaw joint
Incisors
Wolf
Horse
Molars and premolars
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9. Form and Function in Mammals
Mammalian heart
Left atrium
Right atrium
Left ventricle
Right ventricle
Complete division
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10. Form and Function in Mammals
Mammalian Brain
Mammals have large brains in proportion to their body size. Most of the brain is taken up by an enlarged cerebrum, which contains a well-developed cerebral cortex.
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11. Form and Function in Mammals
The limbs and digits (fingers and toes) of many mammals are adapted to their particular way of life. Note the variety of lengths and shapes of the limb bones. Homologous bones are the same color in all the drawings.
The limbs and digits (fingers and toes) of many mammals are adapted to their particular way of life. Note the variety of lengths and shapes of the limb bones that different mammals use for movement. Homologous bones are the same color in all the drawings.
Seal
Mole
Bat
Horse
Monkey
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32-1
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32-1
One characteristic commonly used to determine whether fossils are mammals is
subcutaneous fat.
mammary glands.
a jaw joint that allows movement from side to side.
hair or fur.
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32-1
How many chambers do mammalian hearts have? 2 3 4 6
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32-1
Mammals are called endotherms because they
produce milk to nourish their young.
have well-developed sense organs.
have powerful jaws and specialized teeth.
generate their body heat internally.
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32-1
The first true mammals appeared in the fossil record
soon after the extinction of the dinosaurs.
about the same time as the first reptiles.
during the Triassic when dinosaurs were the dominant land animals.
long after the extinction of the dinosaurs.
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17. END OF SECTION