Cat

The cat (or domestic cat, house cat) is a small carnivorous mammal that is often valued by humans for its companionship and its ability to destroy vermin. It has been associated with humans for at least 9,500 years.[2] A skilled predator, the cat is known to hunt over 1,000 species for food. The cat is intelligent and can be trained to obey simple commands. Individual cats have also been known to learn to manipulate simple mechanisms (see cat intelligence). Cats use a variety of vocalizations and types of body language for communication, including mewing ("meow" or "miaow"), purring, hissing, growling, squeaking, chirping, clicking, and grunting.

Anatomy and morphology

Cats typically weigh between 2.5 and 7 kg (5.5–16 pounds); however, some breeds, such as the Maine Coon can exceed 11.3 kg (25 pounds). Some have been known to reach up to 23 kg (50 pounds) due to overfeeding. Conversely, very small cats (less than 1.8 kg / 4.0 lbs)[4] have been reported.

Cats also possess rather loose skin; this enables them to turn and confront a predator or another cat in a fight, even when it has a grip on them. This is also an advantage for veterinary purposes, as it simplifies injections.[5] In fact, the life of cats with kidney failure can sometimes be extended for years by the regular injection of large volumes of fluid subcutaneously, which serves as an alternative to dialysis.[6][7]
The particularly loose skin at the back of the neck is known as the scruff, and is the area by which a mother cat grips her kittens to carry them. As a result, cats have a tendency to relax and become quiet and passive when gripped there. This tendency often extends into adulthood, and can be useful when attempting to treat or move an uncooperative cat. However, since an adult cat is quite a bit heavier than a kitten, a pet cat should never be carried by the scruff, but should instead have their weight supported at the rump and hind legs, and also at the chest and front paws. Often (much like a small child) a cat will lie with its head and front paws over a person's shoulder, and its back legs and rump supported under the person's arm.

Like almost all mammals, cats possess seven cervical vertebrae. They have thirteen thoracic vertebrae (compared to twelve in humans), seven lumbar vertebrae (compared to five in humans), three sacral vertebrae like most mammals (humans have five because of their bipedal posture), and twenty-two or twenty-three caudal vertebrae (humans have three to five, fused into an internal coccyx). The extra lumbar and thoracic vertebrae account for the cat's enhanced spinal mobility and flexibility, compared to humans; the caudal vertebrae form the tail, used by the cat for counterbalance to the body during quick movements.[8]
Cats have highly specialized teeth and a digestive tract suitable to the digestion of meat. The premolar and first molar together compose the carnassial pair on each side of the mouth, which efficiently functions to shear meat like a pair of scissors. While this is present in canines, it is highly developed in felines. The cat's tongue has sharp spines, or papillae, useful for retaining and ripping flesh from a carcass. These papillae are small backward-facing hooks that contain keratin and assist in their grooming.

Dog

The dog (Canis lupus familiaris) is a domestic subspecies of the wolf, a mammal of the Canidae family of the order Carnivora. The term encompasses both feral and pet variants. It is also sometimes used to describe wild canids of other subspecies or species.
Over time, the dog has developed into hundreds of breeds with a great degree of variation. For example, heights at the withers range from just a few inches (such as the Chihuahua) to roughly three feet (such as the Irish Wolfhound); colors vary from white through grays (usually called blue) to black, and browns from light (tan) to dark ("red" or "chocolate") in a tremendous variation of patterns; and coats can be anything from very short to several centimeters long, from coarse hair to something akin to wool,straight or curly, or smooth.

Origins
Some research appears to show that dogs were domesticated from wolves as recently as 15,000 years ago,[1] or perhaps as early as 100,000 years ago based upon recent genetic, fossil and DNA evidence.[2] Other research suggests that dogs have only been domesticated for a much shorter amount of time and were domesticated from populations of wild dogs, which had previously diverged from wolves.[3][4]
New evidence suggests that dogs were first domesticated in East Asia, possibly China,[5] and the first peoples to enter North America took dogs with them from Asia. Genetic research has identified 14 ancient dog breeds, with the oldest being the Chow Chow, Shar Pei, Akita Inu, Shiba Inu and Basenji. Because many of the 14 breeds are associated with China and Japan, the theory that the dog originated in Asia seems to be likely.[5]
As humans migrated around the planet a variety of dog forms migrated with them. The agricultural revolution and subsequent urban revolution led to an increase in the dog population and a demand for specialization. These circumstances would provide the opportunity for selective breeding to create specialized working dogs and pets.