''Alligator prenasalis'' is an

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 ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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 ...

from the

Late Eocene The Priabonian is, in the International Commission on Stratigraphy, ICS's geologic timescale, the latest age (geology), age or the upper stage (stratigraphy), stage of the Eocene epoch (geology), Epoch or series (stratigraphy), Series. It spans ...

period. It is well known, with many fossils having been collected from the Chadron and

Brule Formation The Brule Formation was deposited between 34 and 30 million years ago, roughly the Rupelian age (Oligocene). It occurs as a subunit of the White River Group in South Dakota, Nebraska, Colorado, North Dakota, and Wyoming. It is a sequence of fin ...

s in

South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state, state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Dakota people, Dakota Sioux ...

. The species was first named in 1904, but was originally classified as a

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 ...

in the genus ''Crocodilus''. It was reassigned to the 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 ...

'' in 1918 on the basis of more complete material. It is the earliest known member of the genus ''Alligator''.

Taxonomy

Junior synonyms

Several species of extinct

alligatorine 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 ''A ...

s have been considered

junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

s of ''A. prenasalis''. These include ''Caimanoidea visheri'', named by paleontologist Maurice Mehl in 1916 from fragmentary material, and ''

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. ...

riggsi'', named in 1931 from a single piece of a lower jaw. Both were considered synonymous with the species in 1972 by paleontologist D.W. Higgins. Mehl used two alternate spellings of ''Caimanoidea'' in his 1916 paper: ''Caimanoideus'' and ''Caimanoeda''. Because the name ''Caimanoidea'' is used first and most frequently, it has been considered the valid name of the genus.

Cladistics

''A. prenasalis'' is similar to the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

alligatorine '' Allognathosuchus mooki'' (now known as ''

Navajosuchus mooki ''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 t ...

''). In 1930, American paleontologist

George Gaylord Simpson George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing '' Tempo ...

considered ''A. prenasalis'' (then called ''Caimanoidea'') to be ancestral to ''A. mooki'' because it appeared to be similar but less specialized. ''A. mooki'' was considered to be more specialized because it had a blunt snout, while ''A. prenasalis'' had a broader, flat, and supposedly primitive snout. If ''A. prenasalis'' were an ancestor of ''A. mooki'', it would have to have occurred in the Eocene. Simpson hypothesized that ''A. prenasalis'' appeared at this time and gave rise to ''A. mooki'', which soon became extinct. While ''A. prenasalis'' (a more generalized form) possibly could have descended from ''A. mooki'' (a more specialized form) through what is known as a reversal, the accepted knowledge at the time was that generalists could not arise from specialists. This was called the "law of the unspecialized", first devised by paleontologist

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...

in 1896. More recent phylogenetic analyses have shown flat-snouted alligatorines to form a clade within a larger group of blunt-snouted alligatorines. Therefore, blunt-snouted forms did not form a single, specialized group, but rather a collection of basal taxa, some of which were ancestral to modern forms such as ''

''. ''Alligator'' is usually recovered as a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group with ''A. prenasalis'' as the most basal member of the clade, as shown in the

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:

References

{{Taxonbar, from=Q4732670 prenasalis Eocene crocodylomorphs Eocene reptiles of North America Fossil taxa described in 1904