Module 3: History of Life Search for:
Taxonomy (which literally means “arrangement law”) is the science of classifying organisms to construct internationally shared classification systems with each organism placed into increasingly more inclusive groupings. Think about a grocery store’s organization. One large space is divided into departments, such as produce, dairy, and meats. Then each department further divides into aisles, then each aisle into categories and brands, and then finally a single product. We call this organization from larger to smaller, more specific categories a hierarchical system.
The taxonomic classification system (also called the Linnaean system after its inventor, Carl Linnaeus, a Swedish botanist, zoologist, and physician) uses a hierarchical model. Moving from the point of origin, the groups become more specific, until one branch ends as a single species. For example, after the common beginning of all life, scientists divide organisms into three large categories called domains: Bacteria, Archaea, and Eukarya. Within each domain is a second category called a kingdom. After kingdoms, the subsequent categories of increasing specificity are: phylum, class, order, family, genus, and species (Figure 1).
The kingdom Animalia stems from the Eukarya domain. Figure 1 above shows the classification for the common dog. Therefore, the full name of an organism technically has eight terms. For the dog it is: Eukarya, Animalia, Chordata, Mammalia, Carnivora, Canidae, Canis, and lupus. Notice that each name is capitalized except for species, and the genus and species names are italicized. Scientists generally refer to an organism only by its genus and species, which is its two-word scientific name, or binomial nomenclature. Therefore, the scientific name of the dog is Canis lupus. The name at each level is also a taxon. In other words, dogs are in order Carnivora. Carnivora is the name of the taxon at the order level; Canidae is the taxon at the family level, and so forth. Organisms also have a common name that people typically use, in this case, dog. Note that the dog is additionally a subspecies: the “familiaris” in Canis lupus familiaris. Subspecies are members of the same species that are capable of mating and reproducing viable offspring, but they are separate subspecies due to geographic or behavioral isolation or other factors.
Figure 2 shows how the levels move toward specificity with other organisms. Notice how the dog shares a domain with the widest diversity of organisms, including plants and butterflies. At each sublevel, the organisms become more similar because they are more closely related. Historically, scientists classified organisms using characteristics, but as DNA technology developed, they have determined more precise phylogenies.
At what levels are cats and dogs considered to be part of the same group?
Visit this website to classify three organisms—bear, orchid, and sea cucumber—from kingdom to species. To launch the game, under Classifying Life, click the picture of the bear or the Launch Interactive button.
Recent genetic analysis and other advancements have found that some earlier phylogenetic classifications do not align with the evolutionary past; therefore, researchers must make changes and updates as new discoveries occur. Recall that phylogenetic trees are hypotheses and are modified as data becomes available. In addition, classification historically has focused on grouping organisms mainly by shared characteristics and does not necessarily illustrate how the various groups relate to each other from an evolutionary perspective. For example, despite the fact that a hippopotamus resembles a pig more than a whale, the hippopotamus may be the whale’s closest living relative.
This video provides another introduction to taxonomy and just how it works:
Canis lupus familiarisdog Facebook Twitter
Domestic dogs are now found worldwide. Their wild ancestors, gray wolves occurred in northern hemisphere continental areas, including North America and the Palearctic.
Domestic dogs are found in association with humans worldwide and in a wide variety of habitats.
Domestic dogs come in a bewildering variety of shapes and sizes. They have been selectively bred for millenia for various behaviors, sensory capabilities, and physical attributes, including dogs bred for herding livestock (collies, sheperds, etc.), different kinds of hunting (pointers, hounds, etc.), catching rats (small terriers), guarding (mastiffs, chows), helping fishermen with nets (Newfoundlands, poodles), pulling loads (huskies, St. Bernards), guarding carriages and horsemen (dalmatians), and as companion dogs. Some kinds were even bred simply as lap warmers (Pekingese). Their basic morphology though, no matter how modified, is that of their wild ancestors, gray wolves.
- Range mass
- <1 to 70 kg
- to 154.19 lb
Reproduction in domestic dogs is generally manipulated by humans. Feral males tend to compete amongst themselves for access to receptive females. Some feral domestic dog populations have reverted to ancestral habits where a single male and female pair (the alpha animals) dominate mating in a small, family group, or pack. Other pack members help to care for the offspring of the dominant pair.
Domestic dogs have a gestation period of 9 weeks, after which anywhere from 1 to dozens of puppies can be born, depending on the breed and nutritional status of the mother. Average litter sizes are from 3 to 9 puppies. Male and female dogs usually reach puberty between 6 and 12 months of age; however, the time that a dog actually breeds depends on many social factors, ranging from size of breed (larger dogs need more time before they are ready to breed) and level of confidence a dog must attain before being ready to breed.
Most breeds are seasonally monocyclic, showing signs of heat every 6 months or so. The reproductive cycle has four stages: anestrus, proestrus, estrus, and diestrus. The anestrus period lasts about 2 to 4 months. Proestrus is the time when a bloody discharge first appears in a female. This is the beginning of “heat,” a period that usually last 9 days but that can last up to 28 days. The end of this period is marked by the females acceptance of a male partner. Estrus is the period when the female is sexually receptive and breeding can occur. Ovulation occurs about 24 hours after the acceptance of the male. Ova survive and are capable of being fertilized for about 4 days after ovulation; therefore it is possible for a female to mate with more that one male. Diestrus follows estrus in the nonpregnant cycle, characterized by a state of “pseudopregnancy”, which is followed by a return of the uterus and ovaries to the anestrus, resting state.
- Breeding interval
- Domestic dogs can reproduce at approximately six month intervals, though usually less frequently.
- Breeding season
- Breeding can occur throughout the year.
- Range number of offspring
- 1 (low)
- Average number of offspring
- 3-9
- Average gestation period
- 63 days
- Range age at sexual or reproductive maturity (female)
- 6 to 12 months
- Range age at sexual or reproductive maturity (male)
- 6 to 12 months
Females nurse and care for their puppies until they are weaned at about 8 to 10 weeks of age. In feral domestic dog packs, puppies are cared for by all members of the pack.
Longevity in domestic dogs depends on the care they receive, their breed, and body size. In general, larger breeds have shorter lifespans. Well-cared for animals can live for 12 years or more.
Domestic dogs are similar to their ancestors, wolves, in that they are both pack animals with a complex set of behaviors related to determining the dogs position in the social hierarchy and their mood. There is only one leader in a pack, and often there is a struggle between members of the pack to determine who the leader is. The struggle ends with one animal on top of the other, with the submissive animal lying on its back. The dominant animal places its paw on the chest of the submissive one, and until the submissive animal looks away from the eyes of the dominant animal, the struggle continues. As soon as the submissive animal averts his eyes, he has admitted defeat and the leader of the pack has been determined. Dogs exhibit characteristic postures that reveal their states of mind. The neutral position is when a dog is calmly observing things in the environment. The mouth of a dog in this position may be open or closed. In the alert position, the dogs mouth may be open or closed, depending on the excitement level and environmental temperature. The hairs along the back and shoulders may raise without any intent of the dog to attack. The dog has simply focused his attention on some object and is curious about it. Offensive threat posture: hair raised, teeth showing, nose wrinkled, and growling may be heard. The tail is upright, although it may be wagging. A dog in this stance is ready to attack. Defensive threat: although the dog may be growling and snarling, the ears are laid back, which is a sign of submission in normal dogs, and the tail is hanging down. Greetings: relaxed face, mouth slightly open, loosely pulled back ears, tail wagging. This is the posture dogs assume when playing with family members or other dogs. Play invitation: lowered front part of body while keeping the rear end up. A dog may bark in this invitation to play, but it does not growl excessivly. Submission: body low to the ground, as compact as possible. Ears are drawn back, tail is tucked tightly under body. Submissive dogs pull the corners of their mouths back but do not show their teeth (submissive grin). Some submissive dogs assume the most vulnerable position known to dogs, lying on the backs, exposing their undersides. This position admits ultimate defeat in the struggle of dominance between dogs.
Domestic dogs can be active at any time of the day or night. Feral domestic dogs maintain home ranges that they defend against others and may move around throughout the year.
Domestic dogs use a complex set of communication modes to navigate their social environment. Chemical cues, such as pheromones, communicate information on reproductive status, social status, and mood. Body language is heavily used and various vocalizations are used as well. Social bonding and communication also occurs through touch.
Puppies have different feeding habits than older dogs. A puppy needs twice as much protein and 50% more calories per pound of body weight daily in order to meet its growth requirements. A rapid change in a puppys diet may cause gastrointestinal upsets. Puppies must feed 4 times daily until the age of 3 months, 3 times daily until 6 months and twice daily for the rest of its life. Older dogs feeding habits are different in a couple of ways. The average size dog requires about 30 calories per pound of body weight per day. Interestingly, larger breeds need only 20 calories per pound of weight, while smaller breeds need about 40 calories per pound of body weight. A dogs diet should consist of balanced porportions of proteins, carbohydrates, fats and, of course, water. A dog can go days without food and lose 30% to 40% of its body weight without dying, but a 10% to 15% water loss could be fatal. All-meat diets are not recommended for dogs due to the lack of calcium and iron found in meat. Diet supplements should be avoided. Human foods that can be fatal to dogs include moldy cheese, onions, and chocolate. Feral domestic dogs will eat a variety of foods including animals and fruits.
Because of their association with humans, domestic dogs are not preyed upon by wild predators. However, feral domestic dogs may be preyed upon by any large predator. Often they are killed by other canids, such as wolves and jackals.
Feral domestic dogs impact ecosystems primarily through predation on native wildlife, often resulting in severe population declines, especially of island endemic species.
There are many species of parasites and disease organisms that infect dogs. Some of which can also infect humans.
Economic Importance for Humans: Positive
If trained properly and treated well, dogs are loyal and protective animals. Domestic dogs have been bred to many purposes throughout the millenia, including as draft animals, guards, hunting, herding, and fishing aids, and as lap animals. More recently dogs are employed as guide dogs for the blind, deaf, and disabled, using their keen sense of smell to detect bombs or drugs, and as therapy animals.