70-401: (traditional): (present): Bats are flying mammals of the order Chiroptera ( / k aɪ ˈ r ɒ p t ər ə / ). With their forelimbs adapted as wings , they are the only mammals capable of true and sustained flight . Bats are more agile in flight than most birds, flying with their very long spread-out digits covered with a thin membrane or patagium . The smallest bat, and arguably
140-523: A natural reservoir of many pathogens , such as rabies ; and since they are highly mobile, social, and long-lived, they can readily spread disease among themselves. If humans interact with bats, these traits become potentially dangerous to humans. Some bats are also predators of mosquitoes , suppressing the transmission of mosquito-borne diseases . Depending on the culture, bats may be symbolically associated with positive traits, such as protection from certain diseases or risks, rebirth, or long life, but in
210-969: A 2005 DNA study. A 2013 phylogenomic study supported the two new proposed suborders. Yangochiroptera (as above) [REDACTED] Pteropodidae (megabats) [REDACTED] Megadermatidae (false vampire bats) [REDACTED] horseshoe bats and allies [REDACTED] The 2003 discovery of an early fossil bat from the 52-million-year-old Green River Formation , Onychonycteris finneyi , indicates that flight evolved before echolocative abilities. Onychonycteris had claws on all five of its fingers, whereas modern bats have at most two claws on two digits of each hand. It also had longer hind legs and shorter forearms, similar to climbing mammals that hang under branches, such as sloths and gibbons . This palm-sized bat had short, broad wings, suggesting that it could not fly as fast or as far as later bat species. Instead of flapping its wings continuously while flying, Onychonycteris probably alternated between flaps and glides in
280-415: A ground-level take off. Myzopodidae Emballonuridae Nycteridae Mystacinidae Mormoopidae Mammal A mammal (from Latin mamma 'breast') is a vertebrate animal of the class Mammalia ( / m ə ˈ m eɪ l i . ə / ). Mammals are characterized by the presence of milk -producing mammary glands for feeding their young, a broad neocortex region of
350-894: A major role in the Neolithic Revolution , and 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, and ultimately the development of the first civilizations . Domesticated mammals provided, and continue to provide, power for transport and agriculture, as well as food ( meat and dairy products ), fur , and leather . Mammals are also hunted and raced for sport, kept as pets and working animals of various types, and are used as model organisms in science. Mammals have been depicted in art since Paleolithic times, and appear in literature, film, mythology, and religion. Decline in numbers and extinction of many mammals
420-415: A mixture of proteins , polysaccharides , and water. For additional structure or protection, pliant skeletons may be supported by rigid skeletons. Organisms that have pliant skeletons typically live in water, which supports body structure in the absence of a rigid skeleton. Rigid skeletons are not capable of movement when stressed, creating a strong support system most common in terrestrial animals . Such
490-440: A shift from -k- to -t- (to Modern English bat ) influenced by Latin blatta , ' moth, nocturnal insect ' . The word bat was probably first used in the early 1570s. The name Chiroptera derives from Ancient Greek : χείρ – cheir , ' hand ' and πτερόν – pteron , ' wing ' . The delicate skeletons of bats do not fossilise well; it is estimated that only 12% of bat genera that lived have been found in
560-402: A single tail fin as in the pinnipeds (seals). In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming. The skeleton consists of both fused and individual bones supported and supplemented by ligaments, tendons, muscles and cartilage. It serves as a scaffold which supports organs, anchors muscles, and protects organs such as
630-775: A sister taxon to odd-toed ungulates (Perissodactyla). Euarchontoglires (primates, treeshrews, rodents, rabbits) [REDACTED] Eulipotyphla (hedgehogs, shrews, moles, solenodons) [REDACTED] Chiroptera (bats) [REDACTED] Pholidota (pangolins) [REDACTED] Carnivora (cats, hyenas, dogs, bears, seals, weasels) [REDACTED] [REDACTED] Perissodactyla (horses, tapirs, rhinos) [REDACTED] Cetartiodactyla (camels, ruminants, whales) [REDACTED] [REDACTED] The flying primate hypothesis proposed that when adaptations to flight are removed, megabats are allied to primates by anatomical features not shared with microbats and thus flight evolved twice in mammals. Genetic studies have strongly supported
700-819: A skeleton type used by animals that live in water are more for protection (such as barnacle and snail shells) or for fast-moving animals that require additional support of musculature needed for swimming through water. Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks ) and silicate (for diatoms and radiolarians ). Hydrostatic skeletons are flexible cavities within an animal that provide structure through fluid pressure, occurring in some types of soft-bodied organisms , including jellyfish, flatworms , nematodes , and earthworms. The walls of these cavities are made of muscle and connective tissue. In addition to providing structure for an animal's body, hydrostatic skeletons transmit
770-491: A smaller number of bones than other terrestrial vertebrates. Birds also lack teeth or even a true jaw , instead having evolved a beak , which is far more lightweight. The beaks of many baby birds have a projection called an egg tooth , which facilitates their exit from the amniotic egg. The skeleton, which forms the support structure inside the fish is either made of cartilage as in the Chondrichthyes , or bones as in
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#1732791505058840-535: A vertebral column, and their skeletons vary, including hard-shelled exoskeleton ( arthropods and most molluscs ), plated internal shells (e.g. cuttlebones in some cephalopods ) or rods (e.g. ossicles in echinoderms ), hydrostatically supported body cavities (most), and spicules ( sponges ). Cartilage is a rigid connective tissue that is found in the skeletal systems of vertebrates and invertebrates. The term skeleton comes from Ancient Greek σκελετός ( skeletós ) 'dried up'. Sceleton
910-418: Is quadrupedal , with most mammals using four limbs for terrestrial locomotion ; but in some, the limbs are adapted for life at sea , in the air , in trees or underground . The bipeds have adapted to move using only the two lower limbs, while the rear limbs of cetaceans and the sea cows are mere internal vestiges . Mammals range in size from the 30–40 millimetres (1.2–1.6 in) bumblebee bat to
980-539: Is a type of dense connective tissue . One of the types of tissue that makes up bone tissue is mineralized tissue and this gives it rigidity and a honeycomb-like three-dimensional internal structure. Bones also produce red and white blood cells and serve as calcium and phosphate storage at the cellular level. Other types of tissue found in bones include marrow , endosteum and periosteum , nerves , blood vessels and cartilage. During embryonic development , bones are developed individually from skeletogenic cells in
1050-584: Is an archaic form of the word. Skeletons can be defined by several attributes. Solid skeletons consist of hard substances, such as bone , cartilage , or cuticle . These can be further divided by location; internal skeletons are endoskeletons, and external skeletons are exoskeletons. Skeletons may also be defined by rigidity, where pliant skeletons are more elastic than rigid skeletons. Fluid or hydrostatic skeletons do not have hard structures like solid skeletons, instead functioning via pressurized fluids. Hydrostatic skeletons are always internal. An exoskeleton
1120-463: Is an external skeleton that covers the body of an animal, serving as armor to protect an animal from predators. Arthropods have exoskeletons that encase their bodies, and have to undergo periodic moulting or ecdysis as the animals grow. The shells of molluscs are another form of exoskeleton. Exoskeletons provide surfaces for the attachment of muscles, and specialized appendanges of the exoskeleton can assist with movement and defense. In arthropods,
1190-399: Is cartilage which in mammals is found mainly in the joint areas. In other animals, such as the cartilaginous fishes , which include the sharks , the skeleton is composed entirely of cartilage . The segmental pattern of the skeleton is present in all vertebrates, with basic units being repeated, such as in the vertebral column and the ribcage. Bones are rigid organs that form part of
1260-1146: Is not believed to originate more than 23 mya. Pteropodidae (megabats) [REDACTED] Megadermatidae (false vampire bats) [REDACTED] Craseonycteridae (Kitti's hog-nosed bat) [REDACTED] Rhinopomatidae (mouse-tailed bats) [REDACTED] Hipposideridae (Old World leaf-nosed bats) [REDACTED] Rhinolophidae (horseshoe bats) [REDACTED] Miniopteridae (long winged bat) [REDACTED] Noctilionidae (fisherman bats) [REDACTED] Mormoopidae ( Pteronotus ) [REDACTED] Mystacinidae (New Zealand short-tailed bats) [REDACTED] Thyropteridae (disc-winged bats) Furipteridae [REDACTED] Mormoopidae ( Mormoops ) [REDACTED] Phyllostomidae (New World leaf-nosed bats) [REDACTED] Molossidae (free-tailed bats) [REDACTED] Emballonuridae (sac-winged bats) [REDACTED] Myzopodidae (sucker-footed bats) Emballonuridae ( Taphozous ) [REDACTED] Natalidae (funnel-eared bats) [REDACTED] Vespertilionidae (vesper bats) [REDACTED] Genetic evidence indicates that megabats originated during
1330-572: Is primarily driven by human poaching and habitat destruction , primarily deforestation . Over 70% of mammal species are in the orders Rodentia , Chiroptera , and Eulipotyphla . Mammal classification has been through several revisions since Carl Linnaeus initially defined the class, and at present , no classification system is universally accepted. McKenna & Bell (1997) and Wilson & Reeder (2005) provide useful recent compendiums. Simpson (1945) provides systematics of mammal origins and relationships that had been taught universally until
1400-613: Is the structural frame that supports the body of most animals . There are several types of skeletons, including the exoskeleton , which is a rigid outer shell that holds up an organism's shape; the endoskeleton , a rigid internal frame to which the organs and soft tissues attach; and the hydroskeleton , a flexible internal structure supported by the hydrostatic pressure of body fluids . Vertebrates are animals with an endoskeleton centered around an axial vertebral column , and their skeletons are typically composed of bones and cartilages . Invertebrates are other animals that lack
1470-416: Is used in some invertebrates, for instance in the hinge of bivalve shells or the mesoglea of cnidarians such as jellyfish . Pliant skeletons are beneficial because only muscle contractions are needed to bend the skeleton; upon muscle relaxation, the skeleton will return to its original shape. Cartilage is one material that a pliant skeleton may be composed of, but most pliant skeletons are formed from
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#17327915050581540-693: Is wider and shallower than the male pelvis. Female pelvises also have an enlarged pelvic outlet and a wider and more circular pelvic inlet. The angle between the pubic bones is known to be sharper in males, which results in a more circular, narrower, and near heart-shaped pelvis. Invertebrates are defined by a lack of vertebral column, and they do not have bone skeletons. Arthropods have exoskeletons and echinoderms have endoskeletons. Some soft-bodied organisms, such as jellyfish and earthworms , have hydrostatic skeletons. The skeletons of arthropods , including insects , crustaceans , and arachnids , are cuticle exoskeletons. They are composed of chitin secreted by
1610-473: The Cretaceous . The relationships between these three lineages is contentious, and all three possible hypotheses have been proposed with respect to which group is basal . These hypotheses are Atlantogenata (basal Boreoeutheria), Epitheria (basal Xenarthra) and Exafroplacentalia (basal Afrotheria). Boreoeutheria in turn contains two major lineages— Euarchontoglires and Laurasiatheria . Estimates for
1680-653: The Guadalupian . Mammals originated from cynodonts , an advanced group of therapsids, during the Late Triassic to Early Jurassic . Mammals achieved their modern diversity in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs , and have been the dominant terrestrial animal group from 66 million years ago to the present. The basic mammalian body type
1750-564: The International Union for Conservation of Nature (IUCN) completed a five-year Global Mammal Assessment for its IUCN Red List , which counted 5,488 species. According to research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495, including 96 recently extinct. The word " mammal " is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from
1820-556: The Latin mamma ("teat, pap"). 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 ( echidnas and platypuses ) and therian mammals ( marsupials and placentals ) and all descendants of that ancestor. Since this ancestor lived in the Jurassic period, Rowe's definition excludes all animals from
1890-502: The Osteichthyes . The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. They are supported only by the muscles. The main external features of the fish, the fins , are composed of either bony or soft spines called rays which, with the exception of the caudal fin (tail fin), have no direct connection with
1960-505: The Pacific Ocean , has a shell that is massive in both size and weight. Syrinx aruanus is a species of sea snail with a very large shell. Endoskeletons are the internal support structure of an animal, composed of mineralized tissues , such as the bone skeletons found in most vertebrates. Endoskeletons are highly specialized and vary significantly between animals. They vary in complexity from functioning purely for support (as in
2030-606: The biological classification scheme used, are the primates : apes , monkeys , and lemurs ; the Cetartiodactyla : whales and even-toed ungulates ; and the Carnivora which includes cats , dogs , weasels , bears , seals , and allies. According to Mammal Species of the World , 5,416 species were identified in 2006. These were grouped into 1,229 genera , 153 families and 29 orders. In 2008,
2100-405: The epidermis . The cuticle covers the animal's body and lines several internal organs, including parts of the digestive system. Arthropods molt as they grow through a process of ecdysis , developing a new exoskeleton, digesting part of the previous skeleton, and leaving the remainder behind. An arthropod's skeleton serves many functions, working as an integument to provide a barrier and support
2170-540: The monophyly of bats and the single origin of mammal flight. An independent molecular analysis trying to establish the dates when bat ectoparasites ( bedbugs ) evolved came to the conclusion that bedbugs similar to those known today (all major extant lineages, all of which feed primarily on bats) had already diversified and become established over 100 mya (i.e., long before the oldest records for bats, 52 mya), suggesting that they initially all evolved on non-bat hosts and "bats were colonized several times independently, unless
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2240-474: The ossicles that articulate only with each other. The hyoid bone , which is located in the neck and serves as the point of attachment for the tongue , does not articulate with any other bones in the body, being supported by muscles and ligaments. There are 206 bones in the adult human skeleton, although this number depends on whether the pelvic bones (the hip bones on each side) are counted as one or three bones on each side (ilium, ischium, and pubis), whether
2310-454: The primates (including humans , monkeys and lemurs ), the even-toed ungulates (including pigs , camels , and whales ), and the Carnivora (including cats , dogs , and seals ). Mammals are the only living members of Synapsida ; this clade , together with Sauropsida (reptiles and birds), constitutes the larger Amniota clade. Early synapsids are referred to as " pelycosaurs ." The more advanced therapsids became dominant during
2380-612: The smallest extant mammal , is Kitti's hog-nosed bat , which is 29–34 mm (1.1–1.3 in) in length, 150 mm (5.9 in) across the wings and 2–2.6 g (0.071–0.092 oz) in mass. The largest bats are the flying foxes , with the giant golden-crowned flying fox ( Acerodon jubatus ) reaching a weight of 1.6 kg (3.5 lb) and having a wingspan of 1.7 m (5 ft 7 in). The second largest order of mammals after rodents , bats comprise about 20% of all classified mammal species worldwide, with over 1,400 species. These were traditionally divided into two suborders:
2450-469: The vampire bats feed on blood . Most bats are nocturnal , and many roost in caves or other refuges; it is uncertain whether bats have these behaviours to escape predators . Bats are present throughout the world, with the exception of extremely cold regions. They are important in their ecosystems for pollinating flowers and dispersing seeds; many tropical plants depend entirely on bats for these services. Bats provide humans with some direct benefits, at
2520-436: The 30 metres (98 ft) blue whale —possibly the largest animal to have ever lived. 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 lay eggs. The most species-rich group is the viviparous placental mammals , so named for the temporary organ ( placenta ) used by offspring to draw nutrition from
2590-453: The 65 that is typical in lizards. The skeletons of birds are adapted for flight . The bones in bird skeletons are hollow and lightweight to reduce the metabolic cost of flight. Several attributes of the shape and structure of the bones are optimized to endure the physical stress associated with flight, including a round and thin humeral shaft and the fusion of skeletal elements into single ossifications . Because of this, birds usually have
2660-492: The West, bats are popularly associated with darkness, malevolence, witchcraft, vampires , and death. An older English name for bats is flittermouse , which matches their name in other Germanic languages (for example German Fledermaus and Swedish fladdermus ), related to the fluttering of wings. Middle English had bakke , most likely cognate with Old Swedish natbakka ( ' night-bat ' ), which may have undergone
2730-612: The air. This suggests that this bat did not fly as much as modern bats, but flew from tree to tree and spent most of its time climbing or hanging on branches. The distinctive features of the Onychonycteris fossil also support the hypothesis that mammalian flight most likely evolved in arboreal locomotors, rather than terrestrial runners. This model of flight development, commonly known as the "trees-down" theory, holds that bats first flew by taking advantage of height and gravity to drop down on to prey, rather than running fast enough for
2800-542: The animal ages. Sea urchins have as many as ten variants of stereome structure. Among extant animals, such skeletons are unique to echinoderms, though similar skeletons were used by some Paleozoic animals. The skeletons of echinoderms are mesodermal , as they are mostly encased by soft tissue. Plates of the skeleton may be interlocked or connected through muscles and ligaments. Skeletal elements in echinoderms are highly specialized and take many forms, though they usually retain some form of symmetry. The spines of sea urchins are
2870-415: The animal's body. The skeletons of sea cucumbers are an exception, having a reduced size to assist in feeding and movement. Echinoderm skeletons are composed of stereom , made up of calcite with a monocrystal structure. They also have a significant magnesium content, forming up to 15% of the skeleton's composition. The stereome structure is porous, and the pores fill with connective stromal tissue as
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2940-400: The body, providing appendages for movement and defense, and assisting in sensory perception. Some arthropods, such as crustaceans, absorb biominerals like calcium carbonate from the environment to strengthen the cuticle. The skeletons of echinoderms , such as starfish and sea urchins , are endoskeletons that consist of large, well-developed sclerite plates that adjoin or overlap to cover
3010-558: The brain, fur or hair , and three middle ear bones . These characteristics distinguish them from reptiles and birds , from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 27 orders . The largest orders of mammals, by number of species , are the rodents , bats , and Eulipotyphla (including hedgehogs , moles and shrews ). The next three are
3080-434: The brain, lungs , heart and spinal cord . The biggest bone in the body is the femur in the upper leg, and the smallest is the stapes bone in the middle ear . In an adult, the skeleton comprises around 13.1% of the total body weight, and half of this weight is water. Fused bones include those of the pelvis and the cranium . Not all bones are interconnected directly: There are three bones in each middle ear called
3150-448: The case of sponges ), to serving as an attachment site for muscles and a mechanism for transmitting muscular forces. A true endoskeleton is derived from mesodermal tissue. Endoskeletons occur in chordates , echinoderms, all great apes (including humans), and sponges. Pliant skeletons are capable of movement; thus, when stress is applied to the skeletal structure, it deforms and then regains its original shape. This skeletal structure
3220-812: The clade originating with the last common ancestor of Sinoconodon and living mammals. The earliest-known synapsid satisfying Kemp's definitions is Tikitherium , dated 225 Ma , so the appearance of mammals in this broader sense can be given this Late Triassic date. However, this animal may have actually evolved during the Neogene. As of the early 21st century, molecular studies based on DNA analysis have suggested new relationships among mammal families. Most of these findings have been independently validated by retrotransposon presence/absence data . Classification systems based on molecular studies reveal three major groups or lineages of placental mammals— Afrotheria , Xenarthra and Boreoeutheria —which diverged in
3290-444: The closest thing to an official classification of mammals, despite its known issues. 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 , rats , porcupines , beavers , capybaras , and other gnawing mammals; Chiroptera : bats; and Eulipotyphla : shrews , moles , and solenodons . The next three biggest orders, depending on
3360-418: The coccyx or tail bone is counted as one or four separate bones, and does not count the variable wormian bones between skull sutures. Similarly, the sacrum is usually counted as a single bone, rather than five fused vertebrae. There is also a variable number of small sesamoid bones, commonly found in tendons. The patella or kneecap on each side is an example of a larger sesamoid bone. The patellae are counted in
3430-563: The cost of some disadvantages. Bat dung has been mined as guano from caves and used as fertiliser. Bats consume insect pests, reducing the need for pesticides and other insect management measures. They are sometimes numerous enough and close enough to human settlements to serve as tourist attractions, and they are used as food across Asia and the Pacific Rim . However, fruit bats are frequently considered pests by fruit growers. Due to their physiology, bats are one type of animal that acts as
3500-1308: The divergence times between these three placental groups range from 105 to 120 million years ago, depending on the type of DNA used (such as nuclear or mitochondrial ) and varying interpretations of paleogeographic data. Monotremata Marsupialia Xenarthra Afrotheria Glires Euarchonta [REDACTED] Eulipotyphla Chiroptera Pholidota Carnivora [REDACTED] Perissodactyla [REDACTED] Artiodactyla [REDACTED] Monotremata [REDACTED] Paucituberculata [REDACTED] Didelphimorphia [REDACTED] Microbiotheria Notoryctemorphia [REDACTED] Peramelemorphia [REDACTED] Dasyuromorphia [REDACTED] Diprotodontia [REDACTED] Cingulata [REDACTED] Pilosa [REDACTED] Hyracoidea [REDACTED] Sirenia [REDACTED] Proboscidea [REDACTED] Tubulidentata [REDACTED] Macroscelidea [REDACTED] Afrosoricida [REDACTED] Eulipotyphla [REDACTED] Chiroptera [REDACTED] Pholidota [REDACTED] Carnivora [REDACTED] Perissodactyla [REDACTED] Artiodactyla [REDACTED] Scandentia [REDACTED] Lagomorpha [REDACTED] Skeleton A skeleton
3570-585: The earlier Triassic , despite the fact that Triassic fossils in the Haramiyida have been referred to the Mammalia since the mid-19th century. If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. Ambondro is more closely related to monotremes than to therian mammals while Amphilestes and Amphitherium are more closely related to
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#17327915050583640-481: The early Eocene , and belong within the four major lines of microbats. Two new suborders have been proposed; Yinpterochiroptera includes the Pteropodidae , or megabat family, as well as the families Rhinolophidae , Hipposideridae , Craseonycteridae , Megadermatidae , and Rhinopomatidae . Yangochiroptera includes the other families of bats (all of which use laryngeal echolocation), a conclusion supported by
3710-423: The ectoderm and mesoderm. Most of these cells develop into separate bone, cartilage, and joint cells, and they are then articulated with one another. Specialized skeletal tissues are unique to vertebrates. Cartilage grows more quickly than bone, causing it to be more prominent earlier in an animal's life before it is overtaken by bone. Cartilage is also used in vertebrates to resist stress at points of articulation in
3780-451: The end of the 20th century. However, since 1945, a large amount of new and more detailed information has gradually been found: The paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics . Though fieldwork and lab work progressively outdated Simpson's classification, it remains
3850-528: The endoskeleton of vertebrates. They provide structural support for the body, assist in movement by opposing muscular contraction, and create a protective wall around internal organs. Bones are primarily made of inorganic minerals, such as hydroxyapatite , while the remainder is made of an organic matrix and water. The hollow tubular structure of bones provide considerable resistance against compression while staying lightweight. Most cells in bones are either osteoblasts , osteoclasts , or osteocytes . Bone tissue
3920-543: The evolutionary origin of bats has been grossly underestimated." Fleas , as a group, are quite old (most flea families formed around the end of the Cretaceous), but no analyses have provided estimates for the age of the flea lineages associated with bats. The oldest known members of a different lineage of bat ectoparasites ( bat flies ), however, are from roughly 20 mya, well after the origin of bats. The bat-ectoparasitic earwig family Arixeniidae has no fossil record, but
3990-407: The exoskeleton also assists with sensory perception . An external skeleton can be quite heavy in relation to the overall mass of an animal, so on land, organisms that have an exoskeleton are mostly relatively small. Somewhat larger aquatic animals can support an exoskeleton because weight is less of a consideration underwater. The southern giant clam , a species of extremely large saltwater clam in
4060-483: The first fossil mammals whose colouration has been discovered: both were reddish-brown. Bats were formerly grouped in the superorder Archonta , along with the treeshrews (Scandentia), colugos (Dermoptera), and primates . Modern genetic evidence now places bats in the superorder Laurasiatheria , with its sister taxon as Ferungulata , which includes carnivorans , pangolins , odd-toed ungulates , even-toed ungulates , and cetaceans . One study places Chiroptera as
4130-440: The forces of muscle contraction, allowing an animal to move by alternating contractions and expansions of muscles along the animal's length. The cytoskeleton ( cyto- meaning 'cell' ) is used to stabilize and preserve the form of the cells. It is a dynamic structure that maintains cell shape, protects the cell, enables cellular motion using structures such as flagella , cilia and lamellipodia , and transport within cells such as
4200-631: The fossil record. Most of the oldest known bat fossils were already very similar to modern microbats, such as Archaeopteropus (32 million years ago). The oldest known bat fossils include Archaeonycteris praecursor and Altaynycteris aurora (55-56 million years ago), both known only from isolated teeth. The oldest complete bat skeleton is Icaronycteris gunnelli (52 million years ago), known from two skeletons discovered in Wyoming. The extinct bats Palaeochiropteryx tupaiodon and Hassianycteris kumari , both of which lived 48 million years ago, are
4270-440: The largely fruit-eating megabats , and the echolocating microbats . But more recent evidence has supported dividing the order into Yinpterochiroptera and Yangochiroptera , with megabats as members of the former along with several species of microbats. Many bats are insectivores , and most of the rest are frugivores (fruit-eaters) or nectarivores (nectar-eaters). A few species feed on animals other than insects; for example,
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#17327915050584340-439: The largest type of echinoderm skeletal structure. Some molluscs, such as conchs, scallops, and snails, have shells that serve as exoskeletons. They are produced by proteins and minerals secreted from the animal's mantle . The skeleton of sponges consists of microscopic calcareous or siliceous spicules . The demosponges include 90% of all species of sponges. Their "skeletons" are made of spicules consisting of fibers of
4410-435: The male and female skeletons. The male skeleton, for example, is generally larger and heavier than the female skeleton. In the female skeleton, the bones of the skull are generally less angular. The female skeleton also has wider and shorter breastbone and slimmer wrists. There exist significant differences between the male and female pelvis which are related to the female's pregnancy and childbirth capabilities. The female pelvis
4480-613: The mother during gestation . Most mammals are intelligent , with some possessing large brains, self-awareness , and tool use . Mammals can communicate and vocalize in several ways, including the production of ultrasound , scent marking , alarm signals , singing , echolocation ; and, in the case of humans, complex language . Mammals can organize themselves into fission–fusion societies , harems , and hierarchies —but can also be solitary and territorial . Most mammals are polygynous , but some can be monogamous or polyandrous . Domestication of many types of mammals by humans played
4550-411: The movement of vesicles and organelles , and plays a role in cellular division. The cytoskeleton is not a skeleton in the sense that it provides the structural system for the body of an animal; rather, it serves a similar function at the cellular level. In most vertebrates, the main skeletal component is bone. Bones compose a unique skeletal system for each type of animal. Another important component
4620-658: The protein spongin , the mineral silica , or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges . Cartilage is a connective skeletal tissue composed of specialized cells called chondrocytes that in an extracellular matrix . This matrix is typically composed of Type II collagen fibers, proteoglycans , and water. There are many types of cartilage, including elastic cartilage , hyaline cartilage , fibrocartilage , and lipohyaline cartilage. Unlike other connective tissues, cartilage does not contain blood vessels. The chondrocytes are supplied by diffusion, helped by
4690-459: The skeleton. Cartilage in vertebrates is usually encased in perichondrium tissue. Ligaments are elastic tissues that connect bones to other bones, and tendons are elastic tissues that connect muscles to bones. The skeletons of turtles have evolved to develop a shell from the ribcage, forming an exoskeleton. The skeletons of snakes and caecilians have significantly more vertebrae than other animals. Snakes often have over 300, compared to
4760-431: The spine. They are supported by the muscles which compose the main part of the trunk. Cartilaginous fish, such as sharks, rays, skates, and chimeras, have skeletons made entirely of cartilage. The lighter weight of cartilage allows these fish to expend less energy when swimming. To facilitate the movement of marine mammals in water, the hind legs were either lost altogether, as in the whales and manatees , or united in
4830-548: The therians; as fossils of all three genera are dated about 167 million years ago in the Middle Jurassic , this is a reasonable estimate for the appearance of the crown group. T. S. Kemp has provided a more traditional definition: " Synapsids that possess a dentary – squamosal jaw articulation and occlusion between upper and lower molars with a transverse component to the movement" or, equivalently in Kemp's view,
4900-460: The total, as they are constant. The number of bones varies between individuals and with age – newborn babies have over 270 bones some of which fuse together. These bones are organized into a longitudinal axis, the axial skeleton , to which the appendicular skeleton is attached. The human skeleton takes 20 years before it is fully developed, and the bones contain marrow , which produces blood cells. There exist several general differences between
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