Domestic dog, carnivorous mammal, generally considered the first domesticated animal. The domesticated dog has coexisted with human beings as a working partner and household pet in all eras and cultures since the days of the cave dwellers. It is generally believed that the direct ancestor of the domestic dog is the wolf, originally found throughout Europe, Asia, and North America. Remains of a dog, estimated to be 10,500 years old, have been found in Idaho.
TAXONOMY Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora Family: Canidae Genus: Canis Species: Canis familiaris
ECOLOGY & HABITAT
Little is known about wild dogs of the past but that they are carnivores: hunters and scavengers. This means that they are secondary consumers in web chains. Eventhough they are carnivores they sometimes accept eating green plants. The ecology of dogs right know is that it helps the human in many fields of life. Since the cave dweller times, dogs have been domesticated by humans and it has helped him to hunt, in herding, protection, etc. It has been very important as a work animal and as a psychological support for humans. The habitat of the dog is where it's owner lives. Different dogs have different adaptations to their ancestral habitat but nowadays, this is not applicable.
The skeleton of the dog is the articulated structure, moved by the muscles, that holds the dog's body and protects some organs and the nervous system. It also functions as mineral and blood deposit of the body. The skeleton of a dog is made up of approximately 321 bones: 134 form the axial skeleton (skull, vertebrae, ribs, etc.), and 186 form the appendicular skeleton (appendages). An extra bone has to be added for male dogs which is the penile bone. The dog is a digigraded animal (it walks with it's toes). It lies on it's third phalanges which are protected by palm cushions. The dog's toes are arranged in an angle which gives more facility of rest after running or other activities. The teeth of the dog is composed of 42 teeth which include canines, molars, incisors, etc.
Joints permit the movement of the bones. There are three types of joints in a dog: fixed joints, movable joints, and semi-movable joints. Fixed joints, such as the ones in the skull don't permit any movement but keep the bones together. The semi-movable joints are those that permit a little movement. They are represented in the spinal column. The movable joints are those present in the rest of the bones. Inside of this group of joints there are various types: the hinge, the ball-and-socket, the pivot, and the gliding joints. The most movable joints are present in the appendages. Joints are held together by a fibrous wrapping, the joint capsule, which reinforced by ligaments. Muscles and tendons also help keeping the bones together.
There are three types of muscles in a dog: the skeletal muscle, cardiac muscle, and smooth muscle. The skeletal muscle works in pairs, a flexor and an extensor. It permits the movement of the skeleton and it also moves the skin of the dog (cutaneal muscle is very developed in dogs). The cardiac muscle is the muscle which is exclusively in the heart. The smooth muscle is the one present in the walls of the digestive organs, arteries, veins, in the diaphragm (which separates the two cavities of the body: the thorax and abdomen), and in some other internal organs.
The digestive system of a dog is very similar to a human one. It ensures the ingestion of food and it's transformation (by mechanical and chemical acts) to simple substances which the dog's body can absorb and assimilate. It all starts in the mouth, where food is broken down mechanically and also a little chemically (saliva and teeth). Then they pass through the esophagus to the stomach to the small intestine (only 3 meters long but it has a very strong digestion) and to the large intestine where the...