Orthogenysuchus
Encyclopedia
Orthogenysuchus is an extinct genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of caimanine alligatorid
Alligatoridae
Alligatoridae is a family of crocodylians that includes alligators and caimans.- True alligators :Alligators proper occur in the fluvial deposits of the age of the Upper Chalk in Europe, where they did not die out until the Pliocene age. The true alligators are now restricted to two species, A...

. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s have been found from the Wasatch Beds of the Willwood Formation of Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

, deposited during the early Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 is O. olseni. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

, known as AMNH 5178, is the only known specimen belonging to the genus and consists of a skull lacking the lower jaws. The braincase is filled in by the matrix and most of the suture lines between bones are indescernable, making comparisons with other eusuchian material difficult.

Phylogeny

Orthogenysuchus was first named in 1924 by Charles C. Mook and was referred to as a eusuchian, although not to any particular eusuchian group known at the time. Later publications assigned the genus to Crocodylidae, but more recent analyses propose that it is a pristichampsid or even a synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...

 of Pristichampsus
Pristichampsus
Pristichampsus is an extinct genus of pristichampsid crocodylian that grew to approximately three metres in length....

. In 1999, Orthogenysuchus was placed within a new clade containing the Miocene caimanines Purussaurus
Purussaurus
Purussaurus is an extinct genus of giant caiman that lived in South America during the Miocene epoch, 8 million years ago. It is known from skull material found in the Brazilian, Colombian and Peruvian Amazonia, and northern Venezuela. The estimated skull length for one large individual of the type...

and Mourasuchus
Mourasuchus
Mourasuchus is an extinct genus of giant crocodilian from the Miocene of South America. It was similar in length and weight to Rhamphosuchus...

. Orthogenysuchus predates these genera by around 30 Ma, suggesting that they both had significant ghost lineage
Ghost lineage
A ghost lineage is a phylogenetic lineage that is inferred to exist but has no fossil record....

s.

Furthermore, the 1999 study proposed a clade containing only Orthogenysuchus and Mourasuchus. This clade is similar to the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Nettosuchidae, which was originally constructed in 1965 for Mourasuchus and the newly described Nettosuchus (later shown to be a junior synonym of the genus). However, the clade is based primarily on ambiguous characters as a result of the poor preservation of the holotype of Orthogenysuchus, and thus has not yet been formally described. All unambiguous synapomorphies are based on the nasal region of the skull where the individual bones are easily distinguished. Orthogenysuchus shares with Mourasuchus a characteristically long, broad snout, extremely wide external nares consisting of the nasal aperture and dorsal fossa, and many small maxillary alveoli.

Paleobiology

Orthogenysuchus is representative of the diverse Wasatchian faunas that occurred during the early Eocene in North America. These faunas are also characterized by the appearance or diversification of many chelonians
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...

 such as emydids
Emydidae
Emydidae, commonly called the pond turtles or marsh turtles, is a family of turtles. Previously, several species of Asian box turtle were classified in the family. However, revised taxonomy has separated them to a different family. Now, Emydidae, with the exception of two species of pond turtle,...

 and testudinids
Tortoise
Tortoises are a family of land-dwelling reptiles of the order of turtles . Like their marine cousins, the sea turtles, tortoises are shielded from predators by a shell. The top part of the shell is the carapace, the underside is the plastron, and the two are connected by the bridge. The tortoise...

, as well as the occurrence of rhineurid
Rhineuridae
The Rhineuridae are a monotypic family of worm lizards containing the monotypic genus, Rhineura, which contains the species R. floridana. This species is found only in Florida no further north than the panhandle. No subspecies are currently recognized...

 amphisbaenia
Amphisbaenia
The Amphisbaenia are a usually legless suborder of squamates closely related to lizards and snakes. As many species possess a pink body coloration and scales arranged in rings, they have a superficial resemblance to earthworms. They are very poorly understood, due to their burrowing lifestyle...

ns. This followed a major faunal turnover at the Clarkforkian
Clarkforkian
The Clarkforkian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology , typically set from 56,800,000 to 55,400,000 years BP lasting . It is usually considered to be within the Paleocene, more specifically the...

-Wasatchian
Wasatchian
The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology , typically set from 55,400,000 to 50,300,000 years BP lasting . It is usually considered to be within the Eocene, more specifically the...

 boundary which resulted in the regional disappearance of champsosaurs
Choristodera
Choristodera is an order of semi-aquatic diapsid reptiles which ranged from the Middle Jurassic, or possibly Late Triassic, to at least the early Miocene. Choristoderes have been found in North America, Asia, and Europe. The most common fossils are typically found from the Late Cretaceous to the...

 and the extinction of the alligatorine Ceratosuchus
Ceratosuchus
Ceratosuchus is an extinct genus of alligatorine 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 American Land Mammal Age. Like its modern relatives, Ceratosuchus was a...

.

The presence of Orthogenys in North America during the Eocene suggests that there was a dispersal event of caimans into the continent from South America after the original spread of early alligatorines and caimanines into South America that occurred during the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

-Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...

 boundary
K–T boundary
The K–T boundary is a geological signature, usually a thin band, dated to 65.5 ± 0.3 Ma ago. K is the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period...

.

External links

  • Orthogenysuchus in the Paleobiology Database
    Paleobiology Database
    ' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...

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