The

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Alligatoridae of

crocodylia Crocodilia () is an Order (biology), order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorp ...

ns includes

alligator An alligator, or colloquially gator, is a large reptile in the genus ''Alligator'' of the Family (biology), family Alligatoridae in the Order (biology), order Crocodilia. The two Extant taxon, extant species are the American alligator (''A. mis ...

caiman A caiman ( (also spelled cayman) from Taíno language, Taíno ''kaiman'') is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family (biology), family, the other being alligators. ...

s and their extinct relatives.

Phylogeny

The superfamily

Alligatoroidea Alligatoroidea is one of three superfamilies of crocodylians, the other two being Crocodyloidea and Gavialoidea. Alligatoroidea evolved in the Late Cretaceous period, and consists of the alligators and caimans, as well as extinct members m ...

includes all crocodilians (fossil and extant) that are more closely related to the American alligator than to either the

Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed in sub-Saharan Africa, occurring mostly in the eastern, southern, and ce ...

or the

gharial The gharial (''Gavialis gangeticus''), also known as gavial or fish-eating crocodile, is a crocodilian in the family (biology), family Gavialidae and among the longest of all living crocodilians. Mature females are long, and males . Adult males ...

. This is a stem-based definition for

alligators An alligator, or colloquially gator, is a large reptile in the genus ''Alligator'' of the family Alligatoridae in the order Crocodilia. The two extant species are the American alligator (''A. mississippiensis'') and the Chinese alligator (''A ...

, and is more inclusive than the

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

Alligatoridae. As a crown group, Alligatoridae only includes the

last common ancestor A most recent common ancestor (MRCA), also known as a last common ancestor (LCA), is the most recent individual from which all organisms of a set are inferred to have descended. The most recent common ancestor of a higher taxon is generally assu ...

of all

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

(living) alligators, caimans, and their descendants (living or

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

), whereas Alligatoroidea, as a stem-based group, also includes more basal extinct alligator ancestors that are more closely related to living alligators than to

crocodiles Crocodiles (family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include all extant member ...

or gavialids. When considering only living taxa (

neontology Neontology is a part of biology that, in contrast to paleontology, studies and deals with living (or, more generally, '' recent'') organisms. It is the study of extant taxa (singular: extant taxon): taxa (such as species, genera and families) wi ...

), Alligatoroidea and Alligatoridae contain the same species. The simplified

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below shows Alligatoridae's relationships to other

(living) crocodilians. Alligatoridae contains eight living species: two alligators within Alligatorinae, and the six caimans of

Caimaninae A caiman ( (also spelled cayman) from Taíno ''kaiman'') is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family, the other being alligators. Caimans are native to Central and ...

Phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

studies using molecular DNA consistently resolve their relationships as follows: The below detailed cladogram shows one proposal for the internal relationships within Alligatoridae including fossil species, based on morphological analysis (although the exact alligatoroid phylogeny is still disputed).

Evolution

The superfamily

is thought to have split from the crocodile-gharial lineage in the

late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, about 87 million years ago. '' Leidyosuchus'' of

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

is among the earliest known genera. Fossil alligatoroids have been found throughout Eurasia as land bridges across both the North Atlantic and the

Bering Strait The Bering Strait ( , ; ) is a strait between the Pacific and Arctic oceans, separating the Chukchi Peninsula of the Russian Far East from the Seward Peninsula of Alaska. The present Russia–United States maritime boundary is at 168° 58' ...

have connected North America to Eurasia during the Cretaceous,

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

, and

Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...

periods. Alligators and caimans split in North America during the early Tertiary or late Cretaceous (about 53 million to about 65 million years ago) and the latter reached South America by the Paleogene, before the closure of the

Isthmus of Panama The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...

during the Neogene period. The Chinese alligator split from the American alligator about 33 million years ago and likely descended from a lineage that crossed the Bering land bridge during the Neogene. The modern American alligator is well represented in the fossil record of the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

. The alligator's full

mitochondrial genome Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in ...

was sequenced in the 1990s. The full

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

, published in 2014, suggests that the alligator evolved much more slowly than mammals and birds.

True alligators

The lineage including alligators proper ( Alligatorinae) occurs in the fluvial deposits of the age of the

Upper Chalk The Chalk Group (often just called the Chalk) is the lithostratigraphy, lithostratigraphic unit (a certain number of Stratum, rock strata) which contains the Upper Cretaceous limestone succession in southern and eastern England. The same or simil ...

in Europe, where they died out in the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58A. mississippiensis'' in the

southeastern United States The Southeastern United States, also known as the American Southeast or simply the Southeast, is a geographical List of regions in the United States, region of the United States located in the eastern portion of the Southern United States and t ...

which can grow to and weigh , with unverified sizes of up to , and the small '' A. sinensis'' in the

Yangtze River The Yangtze or Yangzi ( or ) is the longest river in Eurasia and the third-longest in the world. It rises at Jari Hill in the Tanggula Mountains of the Tibetan Plateau and flows including Dam Qu River the longest source of the Yangtze, i ...

, China, which grows to an average of . Their name derives from the Spanish ''el lagarto'', which means "the lizard".

Caimans

In Central and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

, the alligator family is represented by six species of the subfamily

, which differ from the alligator by the absence of a bony septum between the nostrils, and having ventral armour composed of overlapping bony

scute A scute () or scutum (Latin: ''scutum''; plural: ''scuta'' "Scutum (shield), shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of Bird anatomy#Scales, birds. The ter ...

s, each of which is formed of two parts united by a suture. Besides the three species in ''

Caiman A caiman ( (also spelled cayman) from Taíno language, Taíno ''kaiman'') is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family (biology), family, the other being alligators. ...

'', the smooth-fronted caimans in genus '' Paleosuchus'' and the black caiman in ''

Melanosuchus ''Melanosuchus'', from Ancient Greek μέλας (''mélas''), meaning "black", and σούχος (''soúkhos''), meaning "crocodile", is a genus of caiman. The genus is most commonly referred to as the "Black Caimans". The black caiman of South Am ...

'' are described. Caimans tend to be more agile and crocodile-like in their movements, and have longer, sharper teeth than alligators. ''C. crocodilus'', the

spectacled caiman The spectacled caiman (''Caiman crocodilus''), also known as the white caiman, common caiman, and speckled caiman, is a crocodilian in the family Alligatoridae. It is brownish-, greenish-, or yellowish-gray colored and has a spectacle-like ridge ...

, has the widest distribution, from southern Mexico to the northern half of Argentina, and grows to a modest size of about . The largest is the

near-threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature (IUCN) as that may be vulnerable to endangerment in the near future, but it does not currently qu ...

''Melanosuchus niger'', the ''jacaré-açu'' or large or

black caiman The black caiman (''Melanosuchus niger'') is a crocodilian reptile endemic to South America. With a maximum length of around and a mass of over , it is the largest living species of the family Alligatoridae, and the third-largest crocodilian in ...

of the Amazon River basin. Black caimans grow to , with the unverified size of up to . The black caiman and American alligator are the only members of the alligator family that pose the same danger to humans as the larger species of the

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include ...

family. Although caimans have not been studied in depth, scientists have learned their mating cycles (previously thought to be spontaneous or year-round) are linked to the rainfall cycles and the river levels, which increases chances of survival for their offspring.

Taxonomy

† = extinct Crocnest

* Family Alligatoridae ** Subfamily Alligatorinae *** Genus ''

Alligator An alligator, or colloquially gator, is a large reptile in the genus ''Alligator'' of the Family (biology), family Alligatoridae in the Order (biology), order Crocodilia. The two Extant taxon, extant species are the American alligator (''A. mis ...

'' **** † '' Alligator hailensis'' **** † '' Alligator mcgrewi'' **** † '' Alligator mefferdi'' **** ''Alligator mississippiensis'', American alligator **** † '' Alligator olseni'' **** † '' Alligator prenasalis'' **** ''Alligator sinensis'',

Chinese alligator The Chinese alligator (; ), also known as the Yangtze alligator (), China alligator, or historically the muddy dragon, is a crocodilian endemic to China. It and the American alligator (''A. mississippiensis'') are the only living species in th ...

**** † ''

Alligator thomsoni ''Alligator thomsoni'' is an extinct species of alligator that existed during the Early Miocene period. Their range was principally in what is now known as Nebraska, United States.“Alligator Thomsoni Mook 1923 (Alligator).” FossilworksFossilw ...

'' *** Genus † ''

Allognathosuchus ''Allognathosuchus'' (meaning "other jaw crocodile") is an extinct genus of alligatorine crocodylian with a complicated taxonomic history. It was named in 1921. Description ''Allognathosuchus'' was a medium-sized predator up to 1.5 m in length. ...

'' *** Genus † '' Arambourgia'' *** Genus † ''

Ceratosuchus ''Ceratosuchus'' ("horned crocodile") is an extinct genus of alligatorine crocodylian from latest Paleocene rocks of Colorado's Piceance Basin and earliest Eocene rocks of Wyoming's Bighorn Basin in North America, a slice of time known as the ...

'' *** Genus † '' Chrysochampsa'' *** Genus † '' Eoalligator'' *** Genus † '' Hassiacosuchus'' *** Genus † ''

Krabisuchus ''Krabisuchus'' is an extinct genus of alligatoroid crocodylian that lived in what is now Thailand during the Priabonian, Late Eocene. It was first named by paleontologists Jeremy A. Martin and Komsorn Lauprasert in 2010, and the type species is ...

'' *** Genus † '' Navajosuchus''? *** Genus † '' Procaimanoidea'' *** Genus † '' Wannaganosuchus'' ** Subfamily

*** Genus † '' Acresuchus'' *** Genus † '' Bottosaurus'' *** Genus ''

'' **** † '' Caiman brevirostris'' **** ''Caiman crocodilus'',

Spectacled caiman The spectacled caiman (''Caiman crocodilus''), also known as the white caiman, common caiman, and speckled caiman, is a crocodilian in the family Alligatoridae. It is brownish-, greenish-, or yellowish-gray colored and has a spectacle-like ridge ...

**** ''Caiman latirostris'',

Broad-snouted caiman The broad-snouted caiman (''Caiman latirostris'') is a crocodilian in the family Alligatoridae found in eastern and central South America, including the Pantanal habitat of Bolivia, Southeast Brazil, and Paraguay, as well as northern Argentina an ...

**** † '' Caiman lutescans'' **** † '' Caiman venezuelensis'' **** † '' Caiman wannlangstoni'' **** ''Caiman yacare'',

Yacare caiman The yacare caiman (''Caiman yacare''), also known commonly as the jacare caiman, Paraguayan caiman, piranha caiman, red caiman, and southern spectacled caiman, is a species of caiman, a crocodilian in the family Alligatoridae. The species is end ...

*** Genus † '' Centenariosuchus'' *** Genus † '' Chinatichampsus'' *** Genus † '' Culebrasuchus'' *** Genus † '' Eocaiman'' *** Genus † '' Globidentosuchus'' *** Genus † '' Gnatusuchus'' *** Genus † '' Kuttanacaiman'' *** Genus ''

'' **** † '' Melanosuchus fisheri'' **** ''Melanosuchus niger'',

Black caiman The black caiman (''Melanosuchus niger'') is a crocodilian reptile endemic to South America. With a maximum length of around and a mass of over , it is the largest living species of the family Alligatoridae, and the third-largest crocodilian in ...

*** Genus † '' Mourasuchus'' *** Genus † '' Necrosuchus'' *** Genus † '' Orthogenysuchus'' *** Genus '' Paleosuchus'' **** ''Paleosuchus palpebrosus'', Cuvier's dwarf caiman **** ''Paleosuchus trigonatus'', Smooth-fronted caiman *** Genus † ''

Protocaiman ''Protocaiman'' is a caimanine genus of crocodylian first scientifically described, described in 2018. The type species ''Protocaiman peligrensis'' was discovered in Argentina's Salamanca Formation, and lived in Patagonia during the Paleocene epo ...

'' *** Genus † ''

Purussaurus ''Purussaurus'' is an extinct genus of giant caiman that lived in South America during the Miocene epoch, from the Friasian to the Huayquerian in the SALMA classification. It is known from skull material found in the Brazilian and Peruvian Am ...

'' *** Genus † ''

Tsoabichi ''Tsoabichi'' (from Shoshoni language, Shoshone "''tso’abichi’''", meaning "monster") is an extinct genus of caimanine crocodylian. Fossils are known from the Green River Formation in Wyoming, and date back to the Ypresian stage of the Eocene ...

References

External links

"Crocodilians: Natural History & Conservation"
''crocodilian.com''
"Family Alligatoridae Gray 1844 (alligator)"
, ''fossilworks.org''. * * {{Authority control Taxa named by John Edward Gray Crocodilian families Extant Campanian first appearances