Gryposuchinae

Gryposuchinae Temporal range: Late Oligocene - Holocene, 25–0.117 Ma PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Crocodylomorpha
Order:	Crocodilia
Family:	Gavialidae
Subfamily:	†Gryposuchinae Vélez-Juarbe et al., 2007
Subgroups
See text.

Gryposuchinae is an extinct subfamily of gavialid crocodylians. Gryposuchines lived mainly in South America during the Oligocene and Miocene epochs, though "Gavialis" papuensis survived more recently into the Late Pleistocene/Holocene. Most were long-snouted coastal forms. The group was named in 2007 and includes genera such as Gryposuchus and Aktiogavialis.

Description

Gryposuchines have long, narrow snouts and protruding eye sockets. One distinguishing feature of the group is the lack of a large exposure of the prootic bone around the trigeminal foramen, a hole in the side of the braincase wall.^[1]

Classification

Gryposuchinae was named in 2007 as a subfamily of closely related gavialid crocodilians. It was defined as a stem-based taxon including Gryposuchus jessei and all crocodilians more closely related to it than to Gavialis gangeticus (the gharial) or Tomistoma schlegelii (the False gharial).^[1] Other gavialoids from the Americas include thoracosaurs from the Late Cretaceous and Paleocene and long-snouted tomistomines from the Eocene, but neither of these groups are closely related to gryposuchines. The relationship of tomistomines in particular is unclear, as they have also been classified as crocodiles.^[2]

A phylogenetic analysis conducted in the 2007 study found Gryposuchinae to include the genera Aktiogavialis, Gryposuchus, Ikanogavialis, Piscogavialis, and Siquisiquesuchus. Below is a cladogram from the 2007 analysis showing the phylogenetic relationships of gryposuchines among gavialoids:^[1]

Paleobiology

Based on the deposits in which they were found, most gryposuchines lived along coastlines. This distinguishes them from Asian gavialids like the gharial, which live only in freshwater. The ancestors of both gryposuchines and Asian gavialids were probably also coastal animals. Eogavialis, a basal gavialid, is known from both marine and non-marine deposits in Egypt. If it was a coastal animal, it may have been similar to the ancestor of later gavialids including gryposuchines.^[1]

The origin of gryposuchines is unclear. Earlier gavialids that were their probable ancestors are known from Africa and Asia. Traditionally, an African origin has been favored because gavialids would have been more likely to cross the Atlantic Ocean than the longer expanses of the Pacific Ocean. Moreover, warm equatorial currents run across the Atlantic from Africa to the Americas, assisting in travel. The presence Aktiogavialis in the Caribbean supports an Atlantic migration. Being the oldest known gryposuchine, Aktiogavialis was likely in the closest position to the time and location of the radiation.^[1]

Gryposuchines as a whole largely disappeared in the Pliocene, alongside several other gavialid taxa, due to poorly understood factors, though possibly linked to climate changes of the period. However, the Late Pleistocene or Holocene aged "Gavialis" papuensis from the Solomon Islands is a clear gryposuchine, separated from its closest relatives by a temporal barrier of at least 6 million years and a geographical barrier of at least 10,000 km, presumably having reached Melanesia in a similar fashion as Brachylophus and Lapitiguana iguanas, carried by Pacific oceanic currents. Found in association with dugongs and sea turtles, "Gavialis" papuensis was a marine animal like its ancestors, a 2-3 meter long coastoal piscivore so far known only from Murua. Like other Pleistocene gharials, it presumably was hunted to extinction by humanity.^[3]

References