Sierra College Department of Biological Sciences

Discover the Biological Sciences

The introductory information for this site has been contributed as a joint assignment by students in Bio. Sci. 10.

Zoology - Mammalogy

By: Summer Dales


1.) Zoology-Mammalogy

A.) Overview
1) In zoology, mammalogy is the study of mammals - a class of vertebrates (those with backbones) with characteristics such as <>homeothermic <>metabolism, <>fur, four-chambered <>hearts, and complex <>nervous systems. Mammalogy has also been known as "mastology," "theriology," and "therology."
2) Mammalogy branches off into other taxonomically-oriented disciplines such as <>primatology (study of <>primates), <>cetology (study of <>cetaceans), <>equinology (or <>hippology, study of <>horses), and <>cynology (study of <>dogs). There are also many more.

2.) Vertebrate Skeletal Anatomy
A.) Muscles
1) Muscles operate by contracting and typically pulling one bone toward another (flexing a joint) or away from another (extending a joint). The attachment of the muscle on the stationary bone is called the origin and the attachment on the bone which moves when a muscle contracts is called its insertion. By comparing the size and location of the areas of attachment for opposing muscles you can determine the capabilities and relative strengths of the live animal.

B.) Bones
1) Even if all you have is bone it is usually possible to tell how the animal lived. All vertebrates typically have the equivalent bones, but with modifications of fusion or elimination. Long bones of reptiles are a single bone while those of mammals typically are three bones fused together, a main shaft and 2 end caps. Age can be estimated in mammals by the degree of calcification and fusion of the sutures except in marsupials and reptiles, which retain partially open sutures throughout life. Length increases by growth at the sutures and diameter increases by deposition on the outside as in tree rings but with simultaneous removal of bone from the bone marrow cavity on the inside. Bones in old animals lose calcium and become porous and weak. Many of the major bird bones, especially the humerus, are also hollow, but they are filled with air from the respiratory system rather than containing bone marrow. Their respiratory system allows air to take a loop path through a bird‚s body and be exchanged nearly 100% in a respiratory cycle rather than a reversing straight path with only a 50-75% exchange as in mammalian respiratory systems.

C.) The Axial Skeleton
1) Includes 5 kinds of vertebrae. The centrum of a vertebra is made up of at least 3 bones and forms around the original notochord. The neutral arch is two fused bones, which grow up and around the nerve chord. Ribs sometimes fuse to them to form lumbar processes. The lateral areas where vertebrate are supported by the one behind it are called zygapophyses. Those on the front of a vertebrae point up and support the down-turned zygapophyses on the posterior end of the vertebrae in front of it. The first cervical vertebrae, the atlas, supports the skull and the second or axis usually (except in most whales) allows rotation of the head. The remaining five mammalian cervical vertebrae also have paired foramen in the lateral processes to protect the cerebral lrteries. Birds have 12-14 cervical vertebrae which have saddled shaped ends.
2) Thoracic vertebrae have pairs of lateral areas for attachment of the ribs. In terrestrial mammals the median dorsal neural spine is about proportional in size to the head which is supported by the attached ligaments and muscles. Most mammals have 12 thoracic vertebrae but pinnipeds have 14. Thoracic ribs typically attach between adjacent ribs. The shape of 1 rib and thoracic vertebrae will show whether the animal has a wide or narrow rib cage.
3) Large bulky runners typically have highly interlocked lumbar vertebrae for back support and to keep the body aligned. Small flexible runners like rabbits usually have long lumbar processes (fused ribs) which provide leverage for flexing the back. The fully aquatic swimmers which always have the buoyancy of water to support their body have little supporting interlocking of vertebrae, but sometimes alignment structures.
4)Sacral vertebrae are typically fused to provide a solid sacrum to which the pelvis attaches. Mammals have 3-5 sacral vertebrae while living birds have 7-12 vertebrae fused into a large pelvis called a pygostyle.
5) Runners and jumpers have a deep narrow rib cage while walkers or swingers have wider rib cages. Jumpers, like kangaroos and kangaroo rats, usually have small front limbs and a large tail for counterbalance like a tail of a kite. Flyers and swimmers typically have rounded tapered rib cages.
6) Caudal or tail vertebrae can indicate how the animal uses its tail. Tendon guide grooves on the top indicate it can be raised voluntarily, and vice versa. V-shaped chevron bones on the bottom of the tail between the tail vertebrae provide protection for the caudal artery and are found in animals, which have large muscular powerful tails. Chevron bones are fused pairs of caudal ribs.

D.) The appendages
1)A tall slender scapula is typical in runners, while a wide scapula provides more area for deltoid and trapezius muscle attachment and thus more power, (but less speed) such as found in climbers, swingers etc.
2) Practically all climbers and some diggers have rotatable front limbs to help hold on to tree trunks and/or manipulation of their food.
3) The primitive phalange formula for living reptiles and ribs is 2-3-4-5-4 while living mammals typically have 2-3-3-3-3 bones per digit. Plantigrade, or flat-footed, walking with the heel on the ground as in people and bears is generally slow. Digitigrade locomotion is walking on the toes with the heel off the ground and occurs in dogs, cats etc. Unguligrade locomotion is walking only on the hooves or nails and is characterized by a reduced number of light elongate digits such as in deer and antelope and their metacarpal and metarsal bones are often fused. Swingers often have curved individual finger bones with extension stops to reduce the need for muscle mass. The structure of the nails, claws, or hooves is also highly significant. Many rapid runners have light weight limbs with only one or two elongated toes.

E.) Skull
1) Lateral eye socket placement indicate peripheral vision, typical of herbivores.

2) Frontal eye position allows for binocular vision and thus depth perception which is necessary for predatory animals. Eyes are almost universally directed horizontally. The foramen magnum is the opening in the skull through which the spinal cord emerges.

3) Males often have proportionally larger neck and/or jaw muscles which attach to the top rear of the skull.
Ear capsules are typical of animals with sensitive hearing. This is especially well developed in nocturnal animals which have to rely mainly on their ears. Fusion of cranial structures indicates the brain and skull have reached full size.

4) Teeth confirm the food habits. Mammal jaws only contain one bone (dentary) per side and the articular and quadrate bones become the incus and stapes of the ear. Placental mammals with heterodont teeth have a maximum of 44 teeth while marsupials may have more than 44 teeth. Eruption and wear of teeth usually indicate age.
(Zoology, Sierra College)

Interesting Facts Apes VS Human
Apes Humans
Large front limbs vs. small front limbs
Thumb-like big toe and flat foot vs. in-line big toe & foot with arch
Small brained babies & adults vs. large brained babies & adults
Small narrow female pelvis vs. large wide female pelvis
Muzzel w/straight tooth rows vs. flat face w/ arched tooth rows
Knuckle walking vs. upright stance
Power grip vs. precision grip
Bow-legged stance vs. knock-kneed stance
Communication vs. speech and language
Tool use vs. tool making
Fire avoidance vs. fire control
(What is an ape and what is a human hand-out, zoology sierra college)

(return to the "Discover the Biological Sciences" main index page)

W3C Logo: Valid HTML 4.01 Transitional W3C Logo: Valid CSS