Lagomorpha

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The lagomorphs (Lagomorpha, from the Greek lagōs, λαγώς, hare and morphē, μορφή, shape) They are an order belonging to placental mammals, which includes rabbits, hares, and pikes. Until the beginning of the 20th century they had been considered as rodents but there are considerable differences to separate both orders. There are 110 recent species of lagomorphs of which 109 are still extant, including 34 species of pica, 42 species of rabbit, and 33 species of hare.

Lagomorphs have two pairs of upper incisor teeth, compared to the only pair found in rodents. As in rodents, the incisors are continuously growing, but unlike these, in lagomorphs a layer of enamel covers both sides of the incisors. The second pair of incisors, located posterior to the traditional ones, are noticeably smaller. From a strictly anatomical point of view, the bony skeleton, as well as its viscera and muscles, resemble those of artiodactyls.

The oldest found fossils of lagomorphs date back to 65 million years ago, in Mongolia. Among the extinct species, the Nuralagus rex (giant rabbit species) stands out.

Within the order lagomorphs we currently find the families Ochotonidae (picas) and Leporidae (rabbits and hares). It is estimated that both families differentiated during the Oligocene (37 million years ago).

External Anatomy

Rabbits are small to medium-sized mammals, with a body length of between 15 and 30 centimeters for most species, although some hares can reach up to 70 centimeters in body length. The weight of adult animals varies between 0.1 and 7 kilograms; the extinct species Nuralagus rex is believed to weigh up to 12 kilograms.

The tail of hares is usually very short, in whistling hares it is completely absent. The length of the conspicuous hind legs and ears is also variable, the latter being very long especially in species from desert regions due to their use for thermoregulation. The coloration of lagomorphs is usually inconspicuous and camouflages depending on the habitat. Whistling and temperate hares also show seasonal color change to improve camouflage. In many species of hares, some parts of the fur are more conspicuous and are used for communication - this mainly affects the tail (the 'flower'), but also the ears (the 'spoons'). #34;) or to areas of the flanks.

Alaskan HareL. othus)

All lagomorphs have dense fur, with coat types ranging from woolly expressions to stiff, bristly hairs. On the face are conspicuous sensory hairs, known as 'hare's whiskers', which are distributed around the mouth area (mystacial vibrissae) and over the eyes (superciliary vibrissae). Particularly stiff bristles are found on the soles of the feet, which probably have the function of absorbing impacts. Instead, sole pads are often missing, and only whistling hares have toe and wrist pads.

Between the nostrils and the mouth runs a sensory fossa that crosses the upper lip and gives its name to the "harelip" that occurs in humans. The edges of the lip turn inward to form a hairy groove, which is covered with glands and is called the "cheek and cheek organ". The fur on the bridge of the nose is shed regularly during 'nose flashing'. typical of lagomorphs.

Especially in hares, the ears are conspicuously large. They are funnel-shaped and can be moved independently of each other for sound localization. Whistling hares have smaller, rounder pinnae. They are widely attached to the head, have a conspicuous flap of skin on the inner wall, and are usually covered with long hairs. The eyes are large and are located on the side of the head, which allows panoramic vision.

Internal anatomy

Structure of the Skeleton

Mountain hare (Lepus timidus) in summer coat.

European rabbit (Oryctolagus cuniculus)

In the skeleton, the skull of very light construction stands out, strongly perforated in the anterior part in the hares and opened by a triangular cranial window in the whistling hares. The bony plates are very thin-walled. The nasal cavity is very large, as are the eye sockets. An important feature that distinguishes lagomorphs from other mammals is a circular orifice within the orbit (fused optic foramina).

In total, lagomorphs have between 26 and 28 teeth. The dentition bears superficial similarities to that of rodents, but lagomorphs have a second pair of incisors, which only develops pin-shaped and is hidden behind the larger pair (duplicity). The large incisors are covered in enamel, have no root, and grow throughout life. As in rodents, there is a gap (diastema) between the incisor and molar teeth, missing the cusps. The premolars and molars are widely developed and have deep transverse folds, open roots, and also grow for life.

The vertebral column is very flexible and consists of 7 cervical vertebrae, 19 to 22 thoracic and lumbar, 4 sacral, and 7 to 16 caudal. The latter are usually very small and form a correspondingly short tail. The clavicles may be missing at the shoulder girdle. Ten ribs are attached to the thoracic spine, the first eight being attached by the sternum and the last two only cartilaginously. The pelvis is elongated and lies parallel to the sacral spine.

The front legs have five fingers, the first of which, the thumb, is clearly shortened. Unlike those of most rodents, they cannot be used for grasping. The hind legs have four fingers, which are usually clearly elongated. They are shaped like hocks, the thighs are short, and the lower leg bones (fibula and tibia) are fused together to form one strong bone.

Organ Systems

The internal structure of lagomorphs is essentially the same as that of basic-type mammals. Special features are found above all in the structure of the gastrointestinal tract and sexual organs.

The stomach is simply a glandular stomach, followed, as in all other mammals, by the small intestine, which passes into the large intestine and, at the same point, the very large appendix. It can hold about ten times the contents of the stomach and, in whistling hares alone, it is one and a half times longer than the animals themselves. The adjoining vermiform appendage contains a large amount of lymphatic tissue, and in whistling hares there are also several other appendages of similar structure.

The stomach is very difficult to digest because it is rich in cellulose. Therefore, the appendix is the main area of digestion of hares (caecotrophy), in which the pulp of food is broken down with the help of a effective intestinal flora. From the cecum, digested food passes into the large intestine. In order for the released nutrients to benefit the body, the animals have to re-absorb the food gruel. They excrete it in the form of soft fecal pellets (caecotrophs) and swallow them directly again; the nutrients are absorbed during the next passage through the small intestine. Instead, the stool itself is made up of hard fecal pellets. This type of digestion is similar to that of ruminants, but the food is regurgitated, not reabsorbed.

Females have a double uterus (duplex uterus), whose horns open separately into the vagina. In hares the sexual orifice and anus are separated by a dam (perineum), in whistling hares both open instead into a common shallow excretory orifice (Cloaca). The penis of the males is retracted and placed backwards when they are at rest; whistling hares, unlike hares, have a penile bone. A "true" scrotum does not form, since corresponding skin modifications, such as the tunica dartos, are missing; For this reason, we speak of scrotal sacs, in which the testicles are found under the skin. The levator testis muscle (Musculus cremaster) forms a muscular sheath around the testicles.

Lifestyle

Behavior

American whistle rabbit.

Rabbits are mostly ground-dwelling, inhabiting a variety of habitats, from deserts to tropical forests to arctic tundra. They usually live in burrows in the ground, especially the various species of rabbits dig complex dwellings with individual underground chambers. The wild rabbit, for example, has short burrows that end in a padded nest. Other species, such as marsh and water rabbits, build roofed nests with side entrances. Instead, some social and whistling rabbits build more complex habitable structures with multiple chambers, nesting areas, corridors, and multiple exits. There are also whistling hares and red rabbits that use natural burrows and crevices. Most hares that live in more open landscapes use so-called sassen, depressions in the ground where they establish their resting places.

The social structure of hares ranges from solitary species, like most hares, to social family groups, like those found in some rabbits and whistling hares. Whistling hares have a wide range of communication sounds, to which they also owe their German trivial name. Vowel sounds are also present in some other social hares, but not as vocally amplitude. In addition, the tapping with the hind legs is very pronounced, especially as a warning signal in case of potential danger. Posture and the presentation of brightly colored body parts, as well as the use of scents, are also used for communication.

As a general rule, hares are not very defensive and are preyed on by different predators. The most common protection strategy is flight and avoidance of contact with the enemy. As a result, the animals are very alert and skittish and are rarely found further from their burrows. Especially the hares that live in the open field are also fast runners and can skilfully hook to lose their pursuers.

Diet

Rabbits are predominantly herbivorous, feeding primarily on grasses and grasses, although they will also eat roots, twigs, and bark. As already indicated in the anatomy section, they are cecotrophic species. They excrete suitably soft fecal pellets and swallow them directly afterwards, so that the nutrients released during digestion in the appendix can benefit the body.

Some species accumulate stores of hay and other plant parts in their burrows to get them through dry or cold seasons.

Reproduction and development

Many species are characterized by a very high rate of reproduction. However, the reproductive season of most lagomorphs is seasonal, with photoperiod being an important factor in ovulation in females and also in spermatogenesis in males. Under permanent conditions of long days, they tend to reproduce also throughout the year. Tropical species and those that have migrated from temperate climates to tropical regions reproduce throughout the year. If there is no mating during a fertile phase of the female (oestrus), other ovulations occur at short intervals of 7 to 14 days. In addition, in most species another heat occurs only a few hours after the young have been delivered, which is called postpartum heat. Ovulation itself is induced by mating and occurs 10-12 hours later. The mating itself only lasts a few seconds, but it occurs very often one after the other, and the partners can also change.

Depending on the species and climate, gestation lasts between 28 days in wild rabbits and more than 50 days in hare species living in polar regions. Young come to term in all species of hares except true hares (Lepidae) as hares. They are mostly naked or with little hair and are blind. The young open their eyes at 19 days and are usually independent at four weeks. Young hares, on the other hand, already have fully developed eyes and hearing at birth and are already capable of locomotion. For this reason, unlike the other species of hares, true hares do not build special nests for their young. For about two to four weeks, the pups are suckled with a mother's milk rich in fat and protein.

Fossil hare skeleton Palaeolagus haydeni of the United States

The reproductive rate is very high in many hares due to the short gestation and development period, early sexual maturity, and high number of litters with large numbers of young. For example, some whistling hares from steppe regions can have up to five litters a year with 8 to 13 young each, while wild rabbits and some other species have five to seven litters with up to nine young each. However, due to the high enemy pressure, the mortality rate among the animals is also very high.