''Alligator prenasalis'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

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 ...

from the

Late Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "daw ...

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

Brule Formation The Brule Formation was deposited between 33 and 30 million years ago, roughly the Rupelian age (Oligocene). It occurs as a subunit of the White River Formation in Nebraska, Colorado, North Dakota, South Dakota, and Wyoming. It is a sequence of ...

s in

South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. 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 Lakota people, Lakota and Dakota peo ...

. 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 even more loosely to inclu ...

in the genus ''Crocodilus''. It was reassigned to the genus ''Alligator'' 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 The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linna ...

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 leng ...

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

alligatorine '' Allognathosuchus mooki''. 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 (20th century), modern ...

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, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...

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

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

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

References

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