A group of rabbits is known as a colony or nest (or, occasionally, a warren, though this more commonly refers to where the rabbits live).[3] A group of baby rabbits produced from a single mating is referred to as a litter[4] and a group of domestic rabbits living together is sometimes called a herd.[5]
Rabbits and hares were formerly classified in the order Rodentia (rodent) until 1912, when they were moved into a new order, Lagomorpha (which also includes pikas). Below are some of the genera and species of the rabbit.
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Lepus species are precocial, born relatively mature and mobile with hair and good vision, while rabbit species are altricial, born hairless and blind. Hares and some rabbits live a relatively solitary life in a simple nest above the ground, while other rabbits live in social groups in burrows, which are grouped together to form warrens. Hares are generally larger than rabbits, with ears that are more elongated and hind legs that are larger and longer. Descendants of the European rabbit are commonly bred as livestock and kept as pets, whereas no hares have been domesticated; the breed called the Belgian hare is actually a domestic rabbit which has been selectively bred to resemble a hare.
Rabbits have long been domesticated. The European rabbit has been widely kept as livestock, starting in ancient Rome. Selective breeding, which began in the Middle Ages, has generated a wide variety of rabbit breeds, of which many (since the early 19th century) are also kept as pets.[7] Some strains of rabbit have been bred specifically as research subjects.
As livestock, rabbits are bred for their meat and fur. The earliest breeds were important sources of meat, and so became larger than wild rabbits, but domestic rabbits in modern times range in size from dwarf to giant. Rabbit fur, prized for its softness, can be found in a broad range of coat colors and patterns, as well as lengths. The Angora rabbit breed, for example, was developed for its long, silky fur, which is often hand-spun into yarn. Other domestic rabbit breeds have been developed primarily for the commercial fur trade, including the Rex, which has a short plush coat.
Because the rabbit's epiglottis is engaged over the soft palate except when swallowing, the rabbit is an obligate nasal breather. Rabbits have two sets of incisor teeth, one behind the other. This way they can be distinguished from rodents, with which they are often confused.[8] Another difference is that for rabbits, all of their teeth continue to grow, where as for most rodents, only their incisors continue to grow. Carl Linnaeus originally grouped rabbits and rodents under the class Glires; later, they were separated as the scientific consensus is that many of their similarities were a result of convergent evolution. Recent DNA analysis and the discovery of a common ancestor has supported the view that they share a common lineage, so rabbits and rodents are now often grouped together in the superorder Glires.[9]
Since speed and agility are a rabbit's main defenses against predators (including the swift fox), rabbits have large hind leg bones and well-developed musculature. Though plantigrade at rest, rabbits are on their toes while running, assuming a more digitigrade posture. Rabbits use their strong claws for digging and (along with their teeth) for defense.[10] Each front foot has four toes plus a dewclaw. Each hind foot has four toes (but no dewclaw).[11]
Most wild rabbits (especially compared to hares) have relatively full, egg-shaped bodies. The soft coat of the wild rabbit is agouti in coloration (or, rarely, melanistic), which aids in camouflage. The tail of the rabbit (with the exception of the cottontail species) is dark on top and white below. Cottontails have white on the top of their tails.[12]
The anatomy of rabbits' hind limbs is structurally similar to that of other land mammals and contributes to their specialized form of locomotion. The bones of the hind limbs consist of long bones (the femur, tibia, fibula, and phalanges) as well as short bones (the tarsals). These bones are created through endochondral ossification during development. Like most land mammals, the round head of the femur articulates with the acetabulum of the os coxae. The femur articulates with the tibia, but not the fibula, which is fused to the tibia. The tibia and fibula articulate with the tarsals of the pes, commonly called the foot. The hind limbs of the rabbit are longer than the front limbs. This allows them to produce their hopping form of locomotion. Longer hind limbs are more capable of producing faster speeds. Hares, which have longer legs than cottontail rabbits, are able to move considerably faster.[14] Rabbits stay just on their toes when moving; this is called digitigrade locomotion. The hind feet have four long toes that allow for this and are webbed to prevent them from spreading when hopping.[15] Rabbits do not have paw pads on their feet like most other animals that use digitigrade locomotion. Instead, they have coarse compressed hair that offers protection.[16]
Rabbits have muscled hind legs that allow for maximum force, maneuverability, and acceleration that is divided into three main parts: foot, thigh, and leg. The hind limbs of a rabbit are an exaggerated feature. They are much longer than the forelimbs, providing more force. Rabbits run on their toes to gain the optimal stride during locomotion. The force put out by the hind limbs is contributed by both the structural anatomy of the fusion tibia and fibula, and muscular features.[17]
Bone formation and removal, from a cellular standpoint, is directly correlated to hind limb muscles. Action pressure from muscles creates force that is then distributed through the skeletal structures. Rabbits that generate less force, putting less stress on bones are more prone to osteoporosis due to bone rarefaction.[18] In rabbits, the more fibers in a muscle, the more resistant to fatigue. For example, hares have a greater resistance to fatigue than cottontails. The muscles of rabbit's hind limbs can be classified into four main categories: hamstrings, quadriceps, dorsiflexors, or plantar flexors. The quadriceps muscles are in charge of force production when jumping. Complementing these muscles are the hamstrings, which aid in short bursts of action. These muscles play off of one another in the same way as the plantar flexors and dorsiflexors, contributing to the generation and actions associated with force.[19]
Within the order of lagomorphs, the ears are used to detect and avoid predators. In the family Leporidae, the ears are typically longer than they are wide. For example, in black-tailed jackrabbits, their long ears cover a greater surface area relative to their body size, which allows them to detect predators from far away. In contrast with cottontail rabbits, their ears are smaller and shorter, requiring that predators be closer before they can detect them and flee.
Evolution has favored rabbits with shorter ears, so the larger surface area does not cause them to lose heat in more temperate regions. The opposite can be seen in rabbits that live in hotter climates; possessing longer ears with a larger surface area helps with dispersion of heat. Since sound travels less well in arid as opposed to cooler air, longer ears may aid the organism in detecting predators sooner rather than later in warmer temperatures.[20][page needed] Rabbits are characterized by shorter ears than hares.[21][page needed] Rabbits' ears are an important structure to aid thermoregulation as well as in detecting predators due to the way the outer, middle, and inner ear muscles coordinate with one another. The ear muscles also aid in maintaining balance and movement when fleeing predators.[22]
The auricle, also known as the pinna, is a rabbit's outer ear.[23] The rabbit's pinnae represent a fair part of the body surface area. It is theorized that the ears aid in dispersion of heat at temperatures above 30 C (86 F), with rabbits in warmer climates having longer pinnae due to this. Another theory is that the ears function as shock absorbers that could aid and stabilize rabbits' vision when fleeing predators, but this has typically only been seen in hares.[24][page needed] The rest of the outer ear has bent canals that lead to the eardrum or tympanic membrane.[25]
The middle ear, separated by the outer eardrum in the back of the rabbit's skull, contains three bones: the hammer, anvil, and stirrup, collectively called ossicles, which act to decrease sound before it hits the inner ear; in general, the ossicles act as a barrier to the inner ear for sound energy.[25]
Inner ear fluid, called endolymph, receives the sound energy. After receiving the energy. The inner ear comprises two parts: the cochlea that uses sound waves from the ossicles, and the vestibular apparatus that manages the rabbit's position in regard to movement. Within the cochlea a basilar membrane contains sensory hair structures that send nerve signals to the brain, allowing it to recognize different sound frequencies. Within the vestibular apparatus three semicircular canals help detect angular motion.[25]
A dewlap is a longitudinal flap of skin or similar flesh that hangs beneath the lower jaw or neck. It is a secondary sex characteristic in rabbits, caused by the presence of female sex hormones. They develop with puberty. A female rabbit who has been neutered before reaching sexual maturity will not develop a dewlap, and even if a doe is neutered after developing a dewlap, the dewlap will gradually disappear over several months. This also aligns with the results of injecting male rabbits with female sex hormones, specifically the ones from pregnant women's urine. The male rabbits developed dewlaps, which then gradually disappeared once administration had ceased.[26] (This is not the process of the rabbit test, a common way to test for human female pregnancy in the 20th century; the pregnancy test involved dissecting female rabbits after injection with urine to see if their ovaries had enlarged.)[27] While it is unclear exactly what function a dewlap performs, pregnant female rabbits will pluck fur from their dewlaps shortly before giving birth to line a nest for their young.[28] 152ee80cbc
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