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biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...
, dactyly is the arrangement of digits (
finger A finger is a prominent digit (anatomy), digit on the forelimbs of most tetrapod vertebrate animals, especially those with prehensile extremities (i.e. hands) such as humans and other primates. Most tetrapods have five digits (dactyly, pentadact ...
s and toes) on the
hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the Koala#Characteristics, koala (which has two thumb#O ...
s, feet, or sometimes
wing A wing is a type of fin that produces both Lift (force), lift and drag while moving through air. Wings are defined by two shape characteristics, an airfoil section and a planform (aeronautics), planform. Wing efficiency is expressed as lift-to-d ...
s of a
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...
. The term is derived from the Greek word () meaning "finger." Sometimes the suffix "-dactylia" is used. The derived adjectives end with "-dactyl" or "-dactylous."


As a normal feature


Pentadactyly

Pentadactyly (from Greek "five") is the condition of having five digits on each limb. It is traditionally believed that all living
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
s are descended from an ancestor with a pentadactyl limb, although many species have now lost or transformed some or all of their digits by the process of
evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...
. However, this viewpoint was challenged by
Stephen Jay Gould Stephen Jay Gould ( ; September 10, 1941 – May 20, 2002) was an American Paleontology, paleontologist, Evolutionary biology, evolutionary biologist, and History of science, historian of science. He was one of the most influential and widely re ...
in his 1991 essay "Eight (or Fewer) Little Piggies," where he pointed out polydactyly in early tetrapods and described the specializations of digit reduction. Despite the individual variations listed below, the relationship is to the original five-digit model. In reptiles, the limbs are pentadactylous. Dogs have tetradactylous paws but the
dewclaw A dewclaw is a digit – vestigial in some animals – on the foot of many mammals, birds, and reptiles (including some extinct orders, like certain theropods). It commonly grows higher on the leg than the rest of the foot, such that in di ...
makes them pentadactyls. Cats also have dewclaws on their front limbs but not their hind limbs, making them both pentadactyls and tetradactyls.


Tetradactyly

Tetradactyly (from Greek 'four') is the condition of having four digits on a limb, as in many
bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
s,
amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...
s, and theropod
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
s.


Tridactyly

Tridactyly (from Greek 'three') is the condition of having three digits on a limb, as in the
rhinoceros A rhinoceros ( ; ; ; : rhinoceros or rhinoceroses), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates (perissodactyls) in the family (biology), famil ...
and ancestors of the horse such as '' Protohippus'' and '' Hipparion''. These all belong to the Perissodactyla. Some birds also have three toes, including
emu The emu (; ''Dromaius novaehollandiae'') is a species of flightless bird endemism, endemic to Australia, where it is the Tallest extant birds, tallest native bird. It is the only extant taxon, extant member of the genus ''Dromaius'' and the ...
s, bustards, and quail.


Didactyly

Didactyly (from Greek 'two') or bidactyly is the condition of having two digits on each limb, as in the Hypertragulidae and two-toed sloth, ''Choloepus didactylus''. In humans this name is used for an abnormality in which the middle digits are missing, leaving only the thumb and fifth finger, or big and little toes. Cloven-hoofed mammals (such as deer, sheep and cattle – ''
Artiodactyla Artiodactyls are placental mammals belonging to the order (biology), order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof ...
'') have only two digits, as do ostriches.


Monodactyly

Monodactyly (from Greek 'one') is the condition of having a single digit on a limb, as in modern
horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 mi ...
s and other
equidae Equidae (commonly known as the horse family) is the Taxonomy (biology), taxonomic Family (biology), family of Wild horse, horses and related animals, including Asinus, asses, zebra, zebras, and many extinct species known only from fossils. The fa ...
(though one study suggests that the
frog A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...
might be composed of remnants of digits II and IV, rendering horses as not truly monodactyl) as well as sthenurine kangaroos. Functional monodactyly, where the weight is supported on only one of multiple toes, can also occur, as in the theropod
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...
'' Vespersaurus''. The pterosaur '' Nyctosaurus'' retained only the wing finger on the forelimb, rendering it also partially monodactyl.


As a congenital defect

Among humans, the term "five-fingered hand" is sometimes used to mean the abnormality of having five fingers, none of which is a thumb.


Syndactyly

Syndactyly (from Greek 'together') is a condition where two or more digits are fused together. It occurs normally in some
mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s, such as the siamang and most diprotodontid
marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...
s such as kangaroos. It occurs as an unusual condition in humans.


Polydactyly

Polydactyly (from Greek 'many') is when a limb has more than the usual number of digits. This can be: * As a result of congenital abnormality in a normally pentadactyl animal. Polydactyly is very common among domestic cats. For more information, see polydactyly. * Polydactyly in early tetrapod
aquatic animal An aquatic animal is any animal, whether vertebrate or invertebrate, that lives in a body of water for all or most of its lifetime. Aquatic animals generally conduct gas exchange in water by extracting dissolved oxygen via specialised respirato ...
s, such as in '' Acanthostega gunnari'' (Jarvik 1952), one of an increasing number of genera of stem-tetrapods known from the Upper Devonian, which are providing insights into the appearance of tetrapods and the origin of limbs with digits. It also occurs secondarily in some later tetrapods, such as
ichthyosaurs Ichthyosauria is an taxonomy (biology), order of large extinction, extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of ...
. The use of a term normally reserved for congenital defects reflects that it was regarded as an anomaly at the time, as it was believed that all modern tetrapods have either five digits or ancestors that did.


Oligodactyly

Oligodactyly (from Greek 'few') is having too few digits when not caused by an
amputation Amputation is the removal of a Limb (anatomy), limb or other body part by Physical trauma, trauma, medical illness, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as cancer, malign ...
. It is sometimes incorrectly called hypodactyly or confused with aphalangia, the absence of the phalanx bone on one or (commonly) more digits. When ''all'' the digits on a hand or foot are absent, it is referred to as ''adactyly''.


Ectrodactyly

Ectrodactyly Ectrodactyly, split hand, or cleft hand () involves the deficiency or absence of one or more central Digit (anatomy), digits of the hand or foot and is also known as split hand/split foot malformation (SHFM). The hands and feet of people with ec ...
, also known as ''split-hand malformation'', is the congenital absence of one or more central digits of the hands and feet. Consequently, it is a form of oligodactyly. News anchor Bree Walker is probably the best-known person with this condition, which affects about one in 91,000 people. It is conspicuously more common in the
Vadoma The Doma or vaDoma (singular muDoma), also known as Dema or Wadoma, are a tribe living in the Kanyemba region in the north of Zimbabwe, especially in the Hurungwe and Chipuriro districts around the basins of Mwazamutanda River, a tributary of the ...
in
Zimbabwe file:Zimbabwe, relief map.jpg, upright=1.22, Zimbabwe, relief map Zimbabwe, officially the Republic of Zimbabwe, is a landlocked country in Southeast Africa, between the Zambezi and Limpopo Rivers, bordered by South Africa to the south, Bots ...
. Gould Pyle 122.jpg, Tetradactyly Mikhail Tal 1961 Oberhausen.jpg, Tridactyly (
Mikhail Tal Mikhail Tal (9 November 1936 – 28 June 1992) was a Soviet and Latvian chess player and the eighth World Chess Champion. He is considered a creative genius and is widely regarded as Comparison of top chess players throughout history, one ...
) Malformation of fingers and toes.jpg, Didactyly Gould Pyle 124.jpg, Monodactyly


Clinodactyly

Clinodactyly is a medical term describing the curvature of a digit (a finger or toe) in the plane of the palm, most commonly the fifth finger (the "little finger") towards the adjacent fourth finger (the "ring finger"). It is a fairly common isolated anomaly which often goes unnoticed, but also occurs in combination with other abnormalities in certain genetic syndromes, such as Down syndrome, Turner syndrome and Cornelia de Lange syndrome.


In birds


Anisodactyly

Anisodactyly is the most common arrangement of digits in birds, with three toes forward and one back. This is common in songbirds and other
perching bird A passerine () is any bird of the Order (biology), order Passeriformes (; from Latin 'sparrow' and '-shaped') which includes more than half of all bird species. Sometimes known as perching birds, passerines generally have an Dactyly#In birds, ...
s, as well as hunting birds such as
eagle Eagle is the common name for the golden eagle, bald eagle, and other birds of prey in the family of the Accipitridae. Eagles belong to several groups of Genus, genera, some of which are closely related. True eagles comprise the genus ''Aquila ( ...
s, hawks, and falcons. This arrangement of digits helps with perching and/or climbing and clinging. This occurs in Passeriformes, Columbiformes,
Falconiformes The order Falconiformes () is represented by the extant family Falconidae, Falconidae (falcons and caracaras) and a handful of enigmatic Paleogene species. Traditionally, the other bird of prey families New World vulture, Cathartidae (New World v ...
, Accipitriformes,
Galliformes Galliformes is an order (biology), order of heavy-bodied ground-feeding birds that includes turkey (bird), turkeys, chickens, Old World quail, quail, and other landfowl. Gallinaceous birds, as they are called, are important in their ecosystems ...
and a majority of other birds.


Syndactyly

Syndactyly, as it occurs in birds, is like anisodactyly, except that the third and fourth toes (the outer and middle forward-pointing toes), or three toes, are fused together almost to their claws, as in the belted kingfisher (''Megaceryle alcyon''). This is often found in Picocoraciae, though rollers, ground rollers, and Piciformes (who are zygodactyl) are exceptions.


Zygodactyly

Zygodactyly (from Greek , even-numbered) is an arrangement of digits in birds and chameleons, with two toes facing forward (digits 2 and 3) and two back (digits 1 and 4). This arrangement is most common in
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally (scansorial), but others are exclusively arboreal. The hab ...
species, particularly those that climb
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...
trunks or clamber through foliage. Zygodactyly occurs in the
parrot Parrots (Psittaciformes), also known as psittacines (), are birds with a strong curved beak, upright stance, and clawed feet. They are classified in four families that contain roughly 410 species in 101 genus (biology), genera, found mostly in ...
s, woodpeckers (including flickers), cuckoos (including roadrunners), and some owls. Zygodactyl tracks have been found dating to 120–110 million years ago (early
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
), 50 million years before the first identified zygodactyl fossils. All Psittaciformes, Cuculiformes, the majority of Piciformes and the
osprey The osprey (; ''Pandion haliaetus''), historically known as sea hawk, river hawk, and fish hawk, is a diurnal, fish-eating bird of prey with a cosmopolitan range. It is a large raptor, reaching more than in length and a wingspan of . It ...
are zygodactyl.


Heterodactyly

Heterodactyly is like zygodactyly, except that digits 3 and 4 point forward and digits 1 and 2 point back. This is found only in trogons, though the enantiornithean '' Dalingheornis'' might also have had this arrangement.


Pamprodactyly

Pamprodactyly is an arrangement in which all four toes point forward, outer toes (toe 1 and sometimes 4) often if not regularly reversible. It is a characteristic of
swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIF ...
s (Apodidae) and mousebirds (Coliiformes).


Chameleons

The feet of chameleons are organized into bundles of a group of two and a group of three digits which oppose one another to grasp branches in a pincer-like arrangement. This condition has been called zygodactyly or didactyly, but the specific arrangement in chameleons does not fit either definition. The feet of the front limbs in chameleons, for instance, are organized into a medial bundle of digits 1, 2 and 3, and a lateral bundle of digits 4 and 5, while the feet of the hind limbs are organized into a medial bundle of digits 1 and 2, and a lateral bundle of digits 3, 4 and 5. On the other hand, zygodactyly involves digits 1 and 4 opposing digits 2 and 3, which is an arrangement that chameleons do not exhibit in either front or hind limbs.


Aquatic tetrapods

In many secondarily aquatic vertebrates, the non-bony tissues of the forelimbs and/or hindlimbs are fused into a single flipper. Some remnant of each digit generally remains under the soft tissue of the flipper, though digit reduction gradually occurs such as in baleen whales ( mysticeti). Marine mammals evolving flippers represents a classic example of
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
, and by some analyses, parallel evolution. Full webbing of the digits in the manus and/or pes is present in a number of aquatic tetrapods. Such animals include
marine mammal Marine mammals are mammals that rely on marine ecosystems for their existence. They include animals such as cetaceans, pinnipeds, sirenians, sea otters and polar bears. They are an informal group, unified only by their reliance on marine enviro ...
s ( cetaceans, sirenians, and
pinniped Pinnipeds (pronounced ), commonly known as seals, are a widely range (biology), distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals. They comprise the extant taxon, extant families Odobenidae (whose onl ...
s), marine reptiles (modern
sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerh ...
s and extinct ichthyosaurs,
mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains wer ...
s,
plesiosaurs The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...
, metriorhynchids), and flightless aquatic birds such as penguins. Hyperphalangy, or an increase in the number of
phalanges The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...
beyond ancestral mammal and reptile conditions, is present in modern cetaceans and extinct marine reptiles.


Schizodactyly

Schizodactyly is a
primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
term for grasping and clinging with the second and third digit, instead of the thumb and second digit.


See also

*
Artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...
– even-toed ungulates, clade Cetartiodactyla *
Perissodactyl Perissodactyla (, ), or odd-toed ungulates, is an order of Ungulate, ungulates. The order includes about 17 living species divided into three Family (biology), families: Equidae (wild horse, horses, Asinus, asses, and zebras), Rhinocerotidae ( ...
– odd-toed ungulates


References


External links

* {{Congenital malformations and deformations of musculoskeletal system Congenital disorders of musculoskeletal system Zoology Vertebrate anatomy Comparative anatomy Bird anatomy