Two-toed sloth
Choloepus is a genus of mammals of Central and South America, within the family Megalonychidae consisting of two-toed sloths. The two species of Choloepus, Linnaeus's two-toed sloth and Hoffmann's two-toed sloth, are the only surviving members of the family Megalonychidae. A study of retrovirus and mitochondrial DNA suggests that C. didactylus and C. hoffmani diverged 6 to 7 million years ago. Furthermore, based on cytochrome c oxidase subunit I sequences, a similar divergence date between the two populations of C. hofmanni separated by the Andes has been reported. Although similar to the somewhat smaller and slower-moving three-toed sloths, the relationship between the two genera is not close. Recent phylogenetic analyses support analysis of morphological data from the 1970s and 1980s, suggesting the two genera are not related and each adopted its arboreal lifestyle independently, it is unclear from. Though data has been collected on over 33 different species of sloths just by analyzing bone structures, many of the relationships between clades on a phylogenetic tree are unknown.
Both types tend to occupy the same forests. Each genus of sloth has a common ancestor, but what that ancestor was, when it existed, many of its traits remain unknown. There is little evidence to support the hypothesis of diphyly and that they are only similar because of convergent evolution and only a small amount of data to study overall. In fact, most of the evidence to support the hypothesis of diphyly is still based on the same trait that cause the hypothesis to be suggested. One of the largest problems that exists when attempting to identify clades of modern extant tree sloths is the issue of missing links between surviving, living species and their unidentified common ancestors. There are several families of extinct sloths, about which little is known; this missing information causes large holes in phylogenetic trees and makes tracing paths of evolution a daunting task. As a result, there are many versions of the phylogenetic tree that would describe the evolution and relationship between sloths, most of which conclude that convergent evolution is the mechanism that resulted in today’s genera of tree sloths.
Despite a couple of discrepancies in DNA sequencing, it is accepted that extant tree sloth species of the genera Choloepus and Bradypus do not share a recent common ancestor, making them diphyletic to one another and indicating similarities through convergent evolution. This means that the two extant genera evolved analogous traits, such as locomotion methods, size and many other traits independently from one another as opposed to from their last common ancestor. If the theory of convergent evolution between the two species were accepted as true, that would make sloths “one of the most striking examples of convergent evolution known among mammals”. In order to further support this theory, there would need to be more information and data gathered about intermediate species between the extant species and the common ancestor, estimated to have gone extinct over 30 million years ago; the name "two-toed sloth" erroneously describes the number of toes. They have three toes in their feet; the name "two-toed" sloth is misleading, although used.
The name was intended to describe specific anatomical differences between members of the genus Choloepus and Bradypus. However, to describe these differences, the correct name should be two-fingered sloth as the differences occur in the hands, not in the feet, they are larger than three-toed sloths, having a body length of 58 to 70 centimetres, weighing 4 to 8 kilograms. Other distinguishing features include a more prominent snout, longer fur, the absence of a tail. Two-toed sloths spend most of their lives hanging upside down from trees, they cannot walk, so they pull hand-over-hand to move around, at an slow rate. Being predominantly nocturnal, their fur, which grows greenish algae to blend in, is their main source of protection, their body temperatures depend at least on the ambient temperature. Two-toed sloths differ from three-toed sloths in their climbing behavior, preferring to descend head first. Two-toed sloths have a gestation period of six months to a year, depending on the exact species.
The mother gives birth to a single young. The young are born with claws, are weaned after about a month, although they will remain with the mother for several more months, do not reach sexual maturity until the age of three years, in the case of females, or four to five years, in the case of males, they eat leaves, but shoots, nuts, bark, some native flowers, some small vertebrates. In addition, when they cannot find food, they have been known to eat the algae that grow on their fur for nutrients, they have large stomachs, with multiple chambers, which help to ferment the large amount of plant matter they eat. Food can take
Articular processes
The articular processes or zygapophyses of a vertebra, are projections of the vertebra that serve the purpose of fitting with an adjacent vertebra. The actual region of contact is called the articular facet. Articular processes spring from the junctions of the pedicles and laminæ, there are two right and left, two superior and inferior; these stick out of an end of a vertebra to lock with a zygapophysis on the next vertebra, to make the backbone more stable. The superior processes or prezygapophysis project upward from a lower vertebra, their articular surfaces are directed more or less backward; the inferior processes or postzygapophysis project downward from a higher vertebra, their articular surfaces are directed more or less forward and outward. The articular surfaces are coated with hyaline cartilage. In the cervical vertebral column, the articular processes collectively form the articular pillars; these are the bony surfaces palpated just lateral to the spinous processes. Pars interarticularis Zygapophyseal joint This article incorporates text in the public domain from page 97 of the 20th edition of Gray's Anatomy aplab - BioWeb at University of Wisconsin System Articular processes - BlueLink Anatomy - University of Michigan Medical School Atlas image: back_bone28 at the University of Michigan Health System - "Lumbar Vertebral Column, Posterolateral View" Anatomy figure: 02:01-09 at Human Anatomy Online, SUNY Downstate Medical Center - "Superior and lateral views of typical vertebrae."
Photo of model at Waynesburg College skeleton2/inferiorarticularprocess Photo of model at Waynesburg College skeleton2/superiorarticularprocess
Amniote
Amniotes are a clade of tetrapod vertebrates comprising the reptiles and mammals. Amniotes lay their eggs on land or retain the fertilized egg within the mother, are distinguished from the anamniotes, which lay their eggs in water. Older sources prior to the 20th century, may refer to amniotes as "higher vertebrates" and anamniotes as "lower vertebrates", based on the discredited idea of the evolutionary great chain of being. Amniotes are tetrapods that are characterised by having an egg equipped with an amnion, an adaptation to lay eggs on land rather than in water as the anamniotes do. Amniotes include sauropsids, as well as their ancestors, back to amphibians. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes. In eutherian mammals, these membranes include the amniotic sac; these embryonic membranes and the lack of a larval stage distinguish amniotes from tetrapod amphibians. The first amniotes, referred to as "basal amniotes", resembled small lizards and evolved from the amphibian reptiliomorphs about 312 million years ago, in the Carboniferous geologic period.
Their eggs could survive out of the water, allowing amniotes to branch out into drier environments. The eggs could "breathe" and cope with wastes, allowing the eggs and the amniotes themselves to evolve into larger forms; the amniotic egg represents a critical divergence within the vertebrates, one enabling amniotes to reproduce on dry land—free of the need to return to water for reproduction as required of the amphibians. From this point the amniotes spread around the globe to become the dominant land vertebrates. Early in their evolutionary history, basal amniotes diverged into two main lines, the synapsids and the sauropsids, both of which persist into the modern era; the oldest known fossil synapsid is Protoclepsydrops from about 312 million years ago, while the oldest known sauropsid is Paleothyris, in the order Captorhinida, from the Middle Pennsylvanian epoch. Zoologists characterize amniotes in part by embryonic development that includes the formation of several extensive membranes, the amnion and allantois.
Amniotes develop directly into a terrestrial form with a thick stratified epithelium. In amniotes, the transition from a two-layered periderm to a cornified epithelium is triggered by thyroid hormone during embryonic development, rather than by metamorphosis; the unique embryonic features of amniotes may reflect specializations for eggs to survive drier environments. Features of amniotes evolved for survival on land include a sturdy but porous leathery or hard eggshell and an allantois evolved to facilitate respiration while providing a reservoir for disposal of wastes, their kidneys and large intestines are well-suited to water retention. Most mammals do not lay eggs; the ancestors of true amniotes, such as Casineria kiddi, which lived about 340 million years ago, evolved from amphibian reptiliomorphs and resembled small lizards. At the late Devonian mass extinction, all known tetrapods were aquatic and fish-like; because the reptiliomorphs were established 20 million years when all their fishlike relatives were extinct, it appears they separated from the other tetrapods somewhere during Romer's gap, when the adult tetrapods became terrestrial.
The modest-sized ancestors of the amniotes laid their eggs in moist places, such as depressions under fallen logs or other suitable places in the Carboniferous swamps and forests. Indeed, many modern-day amniotes require moisture to keep their eggs from desiccating. Although some modern amphibians lay eggs on land, all amphibians lack advanced traits like an amnion; the amniotic egg formed through a series of evolutionary steps. After internal fertilization and the habit of laying eggs in terrestrial environments became a reproduction strategy amongst the amniote ancestors, the next major breakthrough appears to have involved a gradual replacement of the gelatinous coating covering the amphibian egg with a fibrous shell membrane; this allowed the egg to increase both its size and in the rate of gas exchange, permitting a larger, metabolically more active embryo to reach full development before hatching. Further developments, like extraembryonic membranes and a calcified shell, were not essential and evolved later.
It has been suggested that shelled terrestrial eggs without extraembryonic membranes could still not have been more than about 1 cm in diameter because of diffusion problems, like the inability to get rid of carbon dioxide if the egg was larger. The only way for the eggs to increase in size would be to develop new internal structures specialized for respiration and for waste products; as this happened, it would affect how much the juveniles could grow before they reached adulthood. Fish and amphibian eggs have the embryonic membrane; the amniote egg ev
Mammal
Mammals are vertebrate animals constituting the class Mammalia, characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex, fur or hair, three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals; the largest orders are the rodents and Soricomorpha. The next three are the Primates, the Cetartiodactyla, the Carnivora. In cladistics, which reflect evolution, mammals are classified as endothermic amniotes, they are the only living Synapsida. The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds; the line following the stem group Sphenacodontia split off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals in the early Mesozoic era.
The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, have been among the dominant terrestrial animal groups from 66 million years ago to the present. The basic body type is quadruped, most mammals use their four extremities for terrestrial locomotion. Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale—the largest animal on the planet. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals; the most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Most mammals are intelligent, with some possessing large brains, self-awareness, tool use. Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals and echolocation.
Mammals can organize themselves into fission-fusion societies and hierarchies—but can be solitary and territorial. Most mammals are polygynous. Domestication of many types of mammals by humans played a major role in the Neolithic revolution, resulted in farming replacing hunting and gathering as the primary source of food for humans; this led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, the development of the first civilizations. Domesticated mammals provided, continue to provide, power for transport and agriculture, as well as food and leather. Mammals are hunted and raced for sport, are used as model organisms in science. Mammals have been depicted in art since Palaeolithic times, appear in literature, film and religion. Decline in numbers and extinction of many mammals is driven by human poaching and habitat destruction deforestation. Mammal classification has been through several iterations since Carl Linnaeus defined the class.
No classification system is universally accepted. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself through the new concept of cladistics. Though field work made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in numbers of species are Rodentia: mice, porcupines, beavers and other gnawing mammals. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes and lemurs. According to Mammal Species of the World, 5,416 species were identified in 2006.
These were grouped into 153 families and 29 orders. In 2008, the International Union for Conservation of Nature completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. According to a research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 species included 96 extinct; the word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma. In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes and therian m
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity, they serve to protect the lungs and other internal organs of the thorax. In some animals snakes, ribs may provide support and protection for the entire body. Ribs are classed as flat bones which have a protective role in the body. Humans have 24 ribs, in 12 pairs. All are attached at the back to the thoracic vertebrae, are numbered from 1–12 according to the vertebrae they attach to; the first rib is attached to thoracic vertebra 1. At the front of the body most of the ribs are joined by costal cartilages to the sternum; the ribs connect to the vertebrae with the costovertebral joints. The parts of a rib include the head, body and angle; the head of the rib lies next to a vertebra. The ribs connect to the vertebrae with two costovertebral joints, one on the head and one on the neck.
The head of the rib has an inferior articulating region, separated by a crest. These articulate with the inferior costal facets on the connecting vertebrae; the crest gives attachment to the intra-articulate ligament that joins the rib to the vertebra of the same number, at the intervertebral disc. Another ligament, the radiate ligament joins the head of the rib to the both the body of the upper vertebra and to the body of the lower vertebra; the smaller middle part of the ligament connects to the intervertebral disc. This plane joint is known as the articulation of the head of the rib; the other costovertebral joint is that between the tubercle on the neck and the transverse process of the joining thoracic vertebra of the same rib number, this is known as the costotransverse joint. The superior costotransverse ligament attaches from the non-articular facet of the tubercle to the transverse process of the vertebra; the neck of the rib is a flattened part. The neck is about 3 cm long, its anterior surface is flat and smooth, whilst its posterior is perforated by numerous foramina and its surface rough, to give attachment to the ligament of the neck.
Its upper border presents a rough crest for the attachment of the anterior costotransverse ligament. A tubercle of rib on the posterior surface of the neck of the rib, has two facets one articulating and one non-articulating; the articular facet, is small and oval and is the lower and more medial of the two, connects to the transverse costal facet on the thoracic vertebra of the same rib number. The transverse costal facet is on the end of the transverse process of the lower of the two vertebrae to which the head is connected; the non-articular portion is a rough elevation and affords attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper ribs than in the lower ribs; the first seven sets of ribs, known as "true ribs", are attached to the sternum by the costal cartilages. The first rib is unique and easier to distinguish than other ribs, it is a flat, C-shaped bone. The vertebral attachment can be found just below the neck at the first thoracic vertebra, the majority of this bone can be found above the level of the clavicle.
Ribs 2 through 7 have a more traditional appearance and become longer and less curved as they progress downwards. The following five sets are known as "false ribs", three of these sharing a common cartilaginous connection to the sternum, while the last two are termed floating ribs, they are attached to the vertebrae only, not to the sternum or cartilage coming off of the sternum. In general, human ribs increase in length from ribs 1 through 7 and decrease in length again through rib 12. Along with this change in size, the ribs become progressively oblique from ribs 1 through 9 less slanted through rib 12; the rib cage is separated from the lower abdomen by the thoracic diaphragm. When the diaphragm contracts, the thoracic cavity is expanded, reducing intra-thoracic pressure and drawing air into the lungs; this happens through one of two actions: when the lower ribs the diaphragm connects to are stabilized by muscles and the central tendon is mobile, when the muscle contracts the central tendon is drawn down, compressing the cavity underneath and expanding the thoracic cavity downward.
When the central tendon is stabilized and the lower ribs are mobile, a contraction of the diaphragm elevates the ribs, which works in conjunction with other muscles to expand the thoracic indent upward. Early in the developing embryo, somites form and soon subdivide into three mesodermal components – the myotome and the sclerotome; the vertebrae and ribs develop from the sclerotomes. During the fourth week costal processes have formed on the vertebral bodies; these processes are small, lateral protrusions of mesenchyme that develop in association with the vertebral arches. During the fifth week the costal processes on the thoracic vertebrae become longer to form the ribs. In the sixth week, the costovertebral joints begin to develop and separate the ribs from the vertebrae; the first seven pairs of ribs, the true ribs join at the front to the sternal bars. By the fetal stage the sternal bars have fused; the ribs begin as cartilage that ossifies – a process called endochondral ossification. Primary ossification centers are located near the angle of each rib, ossification continues in the direction away from the head and neck.
During adolescence secondary ossification centers are formed in the tubercles and he
Joint
A joint or articulation is the connection made between bones in the body which link the skeletal system into a functional whole. They are constructed to allow for different types of movement; some joints, such as the knee and shoulder, are self-lubricating frictionless, are able to withstand compression and maintain heavy loads while still executing smooth and precise movements. Other joints such as sutures between the bones of the skull permit little movement in order to protect the brain and the sense organs; the connection between a tooth and the jawbone is called a joint, is described as a fibrous joint known as a gomphosis. Joints are classified both functionally. Joints are classified structurally and functionally. Structural classification is determined by how the bones connect to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the two types of classifications. Monoarticular – concerning one joint oligoarticular or pauciarticular – concerning 2–4 joints polyarticular – concerning 5 or more joints Structural classification names and divides joints according to the type of binding tissue that connects the bones to each other.
There are four structural classifications of joints: fibrous joint – joined by dense regular connective tissue, rich in collagen fibers cartilaginous joint – joined by cartilage. There are two types: primary cartilaginous joints composed of hyaline cartilage, secondary cartilaginous joints composed of hyaline cartilage covering the articular surfaces of the involved bones with fibrocartilage connecting them. Synovial joint – not directly joined – the bones have a synovial cavity and are united by the dense irregular connective tissue that forms the articular capsule, associated with accessory ligaments. Facet joint – joint between two articular processes between two vertebrae. Joints can be classified functionally according to the type and degree of movement they allow: Joint movements are described with reference to the basic anatomical planes. Synarthrosis – permits little or no mobility. Most synarthrosis joints are fibrous joints. Amphiarthrosis – permits slight mobility. Most amphiarthrosis joints are cartilaginous joints.
Synovial joint – movable. Synovial joints can in turn be classified into six groups according to the type of movement they allow: plane joint and socket joint, hinge joint, pivot joint, condyloid joint and saddle joint. Joints can be classified, according to the number of axes of movement they allow, into nonaxial, monoaxial and multiaxial. Another classification is according to the degrees of freedom allowed, distinguished between joints with one, two or three degrees of freedom. A further classification is according to the number and shapes of the articular surfaces: flat and convex surfaces. Types of articular surfaces include trochlear surfaces. Joints can be classified based on their anatomy or on their biomechanical properties. According to the anatomic classification, joints are subdivided into simple and compound, depending on the number of bones involved, into complex and combination joints: Simple joint: two articulation surfaces Compound joint: three or more articulation surfaces Complex joint: two or more articulation surfaces and an articular disc or meniscus The joints may be classified anatomically into the following groups: Joints of hand Elbow joints Wrist joints Axillary articulations Sternoclavicular joints Vertebral articulations Temporomandibular joints Sacroiliac joints Hip joints Knee joints Articulations of footUnmyelinated nerve fibers are abundant in joint capsules and ligaments as well as in the outer part of intraarticular menisci.
These nerve fibers are responsible for pain perception. Damaging the cartilage of joints or the bones and muscles that stabilize the joints can lead to joint dislocations and osteoarthritis. Swimming is a great way to exercise the joints with minimal damage. A joint disorder is termed arthropathy, when involving inflammation of one or more joints the disorder is called arthritis. Most joint disorders involve arthritis, but joint damage by external physical trauma is not termed arthritis. Arthropathies are called polyarticular when involving many joints and monoarticular when involving only a single joint. Arthritis is the leading cause of disability in people over the age of 55. There are many different forms of arthritis; the most common form of arthritis, occurs following trauma to the joint, following an infection of the joint or as a result of aging and the deterioration of articular cartilage. Furthermore, there is emerging evidence that abnormal anatomy may contribute to early development of osteoarthritis.
Other forms of arthritis are rheumatoid arthritis and psoriatic arthritis, which are autoimmune diseases in which the body is attacking itself. Septic arthritis is caused by joint infection. Gouty arthritis is caused by deposition of uric acid crystals in the joint that results in subsequent inflammation. Additionally, there is a less common form of gout, caused by the formation of rhomboidal-shaped crystals of calcium pyrophosphate; this form of gout is known as pseudogout. Temporomandibular joint syndrome involves the jaw joints and can cause facial p
Manatee
Manatees are large aquatic herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living species in the order Sirenia: the Amazonian manatee, the West Indian manatee, the West African manatee, they measure up to 4.0 metres long, weigh as much as 590 kilograms, have paddle-like flippers. The etymology of the name is dubious, with connections having been made to Latin "manus", to a word sometimes cited as "manati" used by the Taíno, a pre-Columbian people of the Caribbean, meaning "breast". Manatees are called sea cows, as they are slow plant-eaters and similar to cows on land, they graze on water plants in tropical seas. Manatees are three of the four living species in the order Sirenia; the fourth is the Eastern Hemisphere's dugong. The Sirenia are thought to have evolved from four-legged land mammals more than 60 million years ago, with the closest living relatives being the Proboscidea and Hyracoidea; the Amazonian's hair color is brownish gray, it has thick wrinkled skin with coarse hair, or "whiskers".
Photos are rare. Manatees weigh 400 to 550 kilograms, average 2.8 to 3.0 metres in length, sometimes growing to 4.6 metres and 1,775 kilograms. At birth, baby manatees weigh about 30 kilograms each; the manatee has a large, prehensile upper lip, used to gather food and eat and for social interaction and communication. Manatees have shorter snouts than the dugongs; the lids of manatees' small spaced eyes close in a circular manner. The adults have no incisor or canine teeth, just a set of cheek teeth, which are not differentiated into molars and premolars; these teeth are replaced throughout life, with new teeth growing at the rear as older teeth fall out from farther forward in the mouth, somewhat as elephants' teeth do. At any time, a manatee has no more than six teeth in each jaw of its mouth, its tail is paddle-shaped, is the clearest visible difference between manatees and dugongs. The female manatee has two teats, one under each flipper, a characteristic, used to make early links between the manatee and elephants.
The manatee is unusual among mammals in having just six cervical vertebrae, a number that may be due to mutations in the homeotic genes. All other mammals have other than the two-toed and three-toed sloths. Like the horse, the manatee has a simple stomach, but a large cecum, in which it can digest tough plant matter; the intestines are about 45 meters, unusually long for an animal of the manatee's size. Apart from mothers with their young, or males following a receptive female, manatees are solitary animals. Manatees spend 50% of the day sleeping submerged, surfacing for air at intervals of less than 20 minutes; the remainder of the time is spent grazing in shallow waters at depths of 1–2 metres. The Florida subspecies has been known to live up to 60 years. Manatees swim at about 5 to 8 kilometres per hour. However, they have been known to swim at up to 30 kilometres per hour in short bursts. Manatees are capable of understanding discrimination tasks and show signs of complex associative learning.
They have good long-term memory. They demonstrate discrimination and task-learning abilities similar to dolphins and pinnipeds in acoustic and visual studies. Manatees breed once every two years. Gestation lasts about 12 months and to wean the calf takes a further 12 to 18 months. Manatees emit a wide range of sounds used in communication between cows and their calves, their ears are large internally but the external openings are small, they are located four inches behind each eye. Adults communicate to maintain contact and during sexual and play behaviors. Taste and smell, in addition to sight and touch, may be forms of communication. Manatees eat over 60 different freshwater and saltwater plants. Using their divided upper lip, an adult manatee will eat up to 10%–15% of their body weight per day. Consuming such an amount requires the manatee to graze for up to seven hours a day. To be able to cope with the high levels of cellulose in their plant based diet, manatees utilize hindgut fermentation to help with the digestion process.
Manatees have been known to eat small numbers of fish from nets. Manatees use their flippers to "walk" along the bottom whilst they dig for plants and roots in the substrate; when plants are detected, the flippers are used to scoop the vegetation toward the manatee's lips. The manatee has prehensile lips; the lips use seven muscles to tear at plants. Manatees use front flippers to move the plants into the mouth; the manatee does not have front teeth, behind the lips, on the roof of the mouth, there are dense, ridged pads. These horny ridges, the manatee's lower jaw, tear
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