''Aktiogavialis'' 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 ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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 ...

n that lived from the

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

until the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

in what is now the

Caribbean The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the Atlantic Ocean, North Atlantic Ocean, mostly overlapping with the West Indies. Bordered by North America to the north, Central America ...

. Two species have been described: ''Aktiogavialis puertoricensis'' from the Middle Oligocene of

Puerto Rico ; abbreviated PR), officially the Commonwealth of Puerto Rico, is a Government of Puerto Rico, self-governing Caribbean Geography of Puerto Rico, archipelago and island organized as an Territories of the United States, unincorporated territo ...

and ''Aktiogavialis caribesi'' from the

Huayquerian The Huayquerian () age is a period of geologic time (9.0–6.8 Ma) within the Late Miocene epoch of the Neogene, used more specifically within the SALMA classification. It follows the Chasicoan and precedes the Montehermosan age. Etymology T ...

of the Late Miocene of

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

. As a typical

gavialoid Gavialoidea is one of three superfamilies of crocodylians, the other two being Alligatoroidea and Crocodyloidea. Although many extinct species are known, only the gharial ''Gavialis gangeticus'' and the false gharial ''Tomistoma schlegelii'' are ...

, ''Aktiogavialis'' followed the standard

crocodilia Crocodilia () is an 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 crocodylomorph pseudosuchia ...

n body plan. An elongated, squat

quadruped Quadrupedalism is a form of locomotion in which animals have four legs that are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four legs is said to be a quadruped (fr ...

al body terminated in a long, laterally flattened tail at one end, and a specialized, narrow snout at the other. As with the other members of its family, the snout of ''Aktiogavialis'' was extremely long and narrow, tapering into a thin structure past the

eye sockets In anatomy, the orbit is the cavity or socket/hole of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is ...

. Based on the fragmentary remains recovered, the species was differentiated from other members of its family by unique positioning and geometry of its skull elements.

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 ...

analysis indicates its closest relatives were the extinct gavials ''

Gryposuchus ''Gryposuchus'' is an extinct genus of gavialid crocodilian. Fossils have been found from Argentina, Colombia, Venezuela, Brazil and the Peruvian Amazon. The genus existed during the Miocene epoch (Colhuehuapian to Huayquerian). One recently d ...

'' and ''

Siquisiquesuchus ''Siquisiquesuchus'' (meaning " Siquisique crocodile" after the town in Lara, Venezuela, near where the first described specimens were found) is an extinct genus of gavialid crocodilian. It is known from cranial remains and a few postcranial bon ...

''. The type species of the genus, ''A. puertoricensis'', was described in 2007. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

, designated UPRMP 3094, was discovered in Puerto Rican deposits dating around 28 million years old, from the Middle to

Late Oligocene The Chattian is, in the geologic timescale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the pro ...

. The deposits, part of the San Sebastián Formation along the

Río Guatemala The Guatemala River () is a river of San Sebastián, Puerto Rico. Gallery River as seen from the bridge in Guatemala barrio: Río Guatemala, San Sebastián, Puerto Rico 01.jpg Río Guatemala, San Sebastián, Puerto Rico 02.jpg Río Guatemala, S ...

in Puerto Rico, have been an adequate supply of other

crocodylian Crocodilia () is an 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 crocodylomorph pseudosuchian ...

fossils. ''Aktiogavialis'' remains recovered were extremely fragmentary, consisting of an incomplete

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

featuring elements of the

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...

and other scattered cranial elements. Marine sediments and nannofossils form part of the deposits where the specimen was found, indicating a marine distribution for ''A. puertoricensis''. This is in contrast with the living gavialoids, which reside entirely in the freshwater rivers of

South Asia South Asia is the southern Subregion#Asia, subregion of Asia that is defined in both geographical and Ethnicity, ethnic-Culture, cultural terms. South Asia, with a population of 2.04 billion, contains a quarter (25%) of the world's populatio ...

. While fossils found in prehistoric

delta Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...

ic sediments possibly have been washed onto the delta from inland sources, the ''Aktiogavialis'' specimen found so far was from a location that had essentially been

island An island or isle is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics, and oceanic islands, which have never been ...

ic. This has led to conclusions that gavialoids were partially or primarily saltwater reptiles prior to the evolution of the group's one or two

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 ...

species. The genus' name, ''Aktiogavialis'', is derived from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

words ''aktios'' (river) and ''gavialis'' (gavial). This roughly translates to "shore gavial", referring to its rather

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

distribution. The specific name ''puertoricensis'' means "from Puerto Rico", in reference to the specimen's country of origin.

References

Bibliography

* {{Taxonbar, from=Q20718019, from2=Q4701881, from3=Q64831015 Gavialidae Oligocene crocodylomorphs Prehistoric pseudosuchian genera Extinct animals of the Caribbean Fossils of Puerto Rico Fossils of Venezuela Fossil taxa described in 2007