The

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Alligatoridae of

crocodylia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period (Cenomanian stage) and are the closest living ...

ns includes

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

caiman A caiman (also cayman as a variant spelling) is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family, the other being alligators. Caimans inhabit Mexico, Central and South America f ...

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 mor ...

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 throughout sub-Saharan Africa, occurring mostly in the central, eastern, ...

or the gharial. This is a stem-based definition for

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

, and is more inclusive than the crown group Alligatoridae. As a crown group, Alligatoridae only includes the

last common ancestor In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...

of all extant (living) alligators, caimans, and their descendants (living or extinct), 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 even more loosely to include all extant memb ...

gavialids Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial (''Gavialis gangeticus'') and the false gharial (''Tomistoma schlegelii''), both occurring in Asia. ...

. When considering only living taxa (

neontology Neontology is a part of biology that, in contrast to paleontology, 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) with members st ...

), this makes Alligatoroidea and Alligatoridae redundant. The simplified

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

below shows Alligatoridae's relationships to other extant (living) crocodilians. The below detailed cladogram shows one proposal for the internal relationships within Alligatoridae (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 younger 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 ''creta'', ...

, about 87 million years ago. ''

Leidyosuchus ''Leidyosuchus'' (meaning " Leidy's crocodile") is an extinct genus of alligatoroid from the Late Cretaceous of Alberta. It was named in 1907 by Lawrence Lambe, and the type species is ''L. canadensis''. It is known from a number of specimens fro ...

'' of

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

is the earliest known genus. Fossil alligatoroids have been found throughout Eurasia as land bridges across both the North Atlantic and the Bering Strait have connected North America to Eurasia during the Cretaceous, Paleogene, and Neogene 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 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 ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

. The alligator's full

mitochondrial genome Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial ...

was sequenced in the 1990s. The full

genome In the fields of molecular biology and genetics, 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 g ...

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

True alligators

The lineage including alligators proper (

Alligatorinae Alligatorinae is a subfamily within the family Alligatoridae that contains the alligators and their closest extinct relatives, and is the sister taxon to Caimaninae (the caimans). Many genera in Alligatorinae are described, but only the genus ...

) occurs in the fluvial deposits of the age of the Upper Chalk in Europe, where they did not die out until the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58A. mississippiensis'' in the

southeastern United States The Southeastern United States, also referred to as the American Southeast or simply the Southeast, is a geographical region of the United States. It is located broadly on the eastern portion of the southern United States and the southern por ...

, which can grow to 15.6 ft (4.6 m) and weigh 1000 lbs(453 kg), with unverified sizes of up to 19.2 ft(5.9 m). And the small '' A. sinensis'' in the

Yangtze River The Yangtze or Yangzi ( or ; ) is the longest list of rivers of Asia, river in Asia, the list of rivers by length, third-longest in the world, and the longest in the world to flow entirely within one country. It rises at Jari Hill in th ...

, China, which grows to an average of 5 ft (1.5 m). Their name derives from the

Spanish Spanish might refer to: * Items from or related to Spain: **Spaniards are a nation and ethnic group indigenous to Spain **Spanish language, spoken in Spain and many Latin American countries **Spanish cuisine Other places * Spanish, Ontario, Can ...

''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 relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

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

Caimaninae A caiman (also cayman as a variant spelling) is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family, the other being alligators. Caimans inhabit Mexico, Central and South America fr ...

, 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'' "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 birds. The term is also used to describe the anterior po ...

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

Caiman A caiman (also cayman as a variant spelling) is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family, the other being alligators. Caimans inhabit Mexico, Central and South America f ...

'', the smooth-fronted caimans in genus ''

Paleosuchus ''Paleosuchus'' is a South American genus of reptiles in the subfamily Caimaninae of the family Alligatoridae. They are the smallest members of the order Crocodilia in the Americas The Americas, which are sometimes collectively called ...

'' and the black caiman in '' Melanosuchus'' 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, 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 as that may be vulnerable to endangerment in the near future, but it does not currently qualify f ...

''Melanosuchus niger'', the ''jacaré-açu'' or large or black caiman of the Amazon River basin. Black caimans grow to , with the unverified size of up to . The black caiman and

American alligator The American alligator (''Alligator mississippiensis''), sometimes referred to colloquially as a gator or common alligator, is a large crocodilian reptile native to the Southeastern United States. It is one of the two extant species in the gen ...

are the only members of the alligator family that pose the same danger to humans as the larger species of the crocodile 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

Caïman de Schneider (Paleosuchus trigonatus)

* Family Alligatoridae ** Subfamily

*** Genus ''

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

'' **** † ''

Alligator hailensis ''Alligator hailensis'', or Haile alligator, is a large, extinct species of ''Alligator'' known from the early Pleistocene of Florida. It is named after the town of Haile, Florida, where it was found. Its age and skeletal morphology is intermed ...

'' **** † '' Alligator mcgrewi'' **** † ''

Alligator mefferdi ''Alligator mefferdi'' is an extinct species of alligator described by Charles Craig Mook. They lived in the Miocene period, and their range was principally in what is now Nebraska, United States.American alligator The American alligator (''Alligator mississippiensis''), sometimes referred to colloquially as a gator or common alligator, is a large crocodilian reptile native to the Southeastern United States. It is one of the two extant species in the gen ...

**** † ''

Alligator olseni ''Alligator olseni'' (common name Olsen's Alligator, named after Russel Olsen) is an extinct species of alligator. They lived in the Early Miocene period, around 20.4–15.97 million years ago and possibly earlier. Their range was principally in ...

'' **** † ''

Alligator prenasalis ''Alligator prenasalis'' is an extinct species of alligator from the Late Eocene period. It is well known, with many fossils having been collected from the Chadron and Brule Formations in South Dakota. The species was first named in 1904, but wa ...

'' **** ''Alligator sinensis'', Chinese alligator **** † '' Alligator thomsoni'' *** 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 leng ...

'' *** Genus † ''

Arambourgia ''Arambourgia'' is an extinct monotypic genus of alligatorine crocodylian from Europe. It was named in 1905 as ''Allognathosuchus gaudryi''. It was made a separate genus ''Arambourgia'' in 1940. This was synonymized with '' Allognathosuchus hau ...

'' *** Genus † ''

Ceratosuchus ''Ceratosuchus'' 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 Clarkforkian North Am ...

'' *** Genus † ''

Chrysochampsa ''Chrysochampsa'' is an extinct monospecific genus of alligatorine. Fossils have been found from the Golden Valley Formation of North Dakota and date back to the Wasatchian regional North American faunal stage of the early Eocene. The genus has ...

'' *** Genus † '' Eoalligator'' *** Genus † '' Hassiacosuchus'' *** Genus † '' Krabisuchus'' *** Genus † ''

Navajosuchus ''Navajosuchus'' is an extinct genus of alligatorine crocodylian. Its fossils have been found in the Paleocene-age Nacimiento Formation of the San Juan Basin, New Mexico (United States). It was named in 1942 by Charles C. Mook, and the original ...

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

*** Genus † ''

Acresuchus ''Acresuchus'' ("Acre crocodile") is an extinct monospecific genus of medium-sized caiman from the Late Miocene of western Brazil andVenezuela. The genus contains a single species, ''Acresuchus pachytemporalis''. ''Acresuchus'' is a close relativ ...

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

'' **** † '' Caiman brevirostris'' **** ''Caiman crocodilus'', Spectacled caiman **** ''Caiman latirostris'', Broad-snouted caiman **** † '' Caiman lutescans'' **** † '' Caiman venezuelensis'' **** † '' Caiman wannlangstoni'' **** ''Caiman yacare'',

Yacare caiman The yacare caiman (''Caiman yacare''), also known commonly as the jacare caiman, Spanish yacaré, Paraguayan caiman, piranha caiman, red caiman, southern spectacled caiman, ''jacaré'' in Portuguese, and îakaré in Old Tupi, is a species of cai ...

*** Genus † '' Centenariosuchus'' *** Genus † '' Chinatichampsus'' *** Genus † '' Culebrasuchus'' *** Genus † ''

Eocaiman ''Eocaiman'' is an extinct genus of caiman containing species living from the Early Paleocene to Miocene in what is now Argentina (Salamanca Formation, Salamanca and Sarmiento Formations), Itaboraí Formation of Brazil and Colombia (Honda Group, ...

'' *** Genus † ''

Globidentosuchus ''Globidentosuchus'' is an extinct genus of basal caimanine crocodylian known from the late Middle to Late Miocene of the Middle and the Upper Members of the Urumaco Formation at Urumaco, Venezuela. Its skull was very short and robust, with l ...

'' *** Genus † ''

Gnatusuchus ''Gnatusuchus'' is an extinct genus of caiman represented by the type species ''Gnatusuchus pebasensis'' from the Middle Miocene Pebas Formation of Peru. ''Gnatusuchus'' lived about 13 million years ago (Ma) in a large wetland system called t ...

'' *** Genus † '' Kuttanacaiman'' *** Genus '' Melanosuchus'' **** † '' Melanosuchus fisheri'' **** ''Melanosuchus niger'', Black caiman *** Genus † ''

Mourasuchus ''Mourasuchus'' is an extinct genus of giant, aberrant caiman from the Miocene of South America. Its skull has been described as duck-like, being broad, flat, and very elongate, superficially resembling '' Stomatosuchus'' from the Late Cretaceo ...

'' *** Genus † ''

Necrosuchus ''Necrosuchus'' is an extinct genus of caiman from modern day Argentina that lived during the Paleocene epoch (Selandian age, about 60 million years ago). It inhabited the fluvio-lacustrine environment of the Patagonian Salamanca Formation. Hist ...

'' *** Genus † '' Orthogenysuchus'' *** Genus ''

'' **** ''Paleosuchus palpebrosus'',

Cuvier's dwarf caiman Cuvier's dwarf caiman (''Paleosuchus palpebrosus'') is a small crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago ...

**** ''Paleosuchus trigonatus'',

Smooth-fronted caiman The smooth-fronted caiman (''Paleosuchus trigonatus''), also known as Schneider's dwarf caiman or Schneider's smooth-fronted caiman,Protocaiman'' *** 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 Amazo ...

'' *** Genus † '' Tsoabichi''

References

External links

"Crocodilians: Natural History & Conservation"
''crocodilian.com''
"Family Alligatoridae Gray 1844 (alligator)"
''fossilworks.org''. * * {{Taxonbar, from=Q6184764 Taxa named by John Edward Gray Reptile families Extant Campanian first appearances