Gnatusuchus

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Gnatusuchus
Temporal range: Mid Miocene (Laventan), 16–11.6  Ma [1]
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Gnatusuchus skeletal.jpg
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Alligatoridae
Subfamily: Caimaninae
Genus: Gnatusuchus
(Salas-Gismondi et al., 2015)
Type species
Gnatusuchus pebasensis
Salas-Gismondi et al., 2015

Gnatusuchus is an extinct genus of caiman represented by the type species Gnatusuchus pebasensis from the Middle Miocene Pebas Formation of Peru. Gnatusuchus lived about 13 million years ago (Ma) in a large wetland system called the Pebas mega-wetlands that covered over one million square kilometers of what is now the Amazon Basin (the modern basin had not yet developed at that time and instead of draining from west to east into the Atlantic Ocean, river systems drained northward through the wetlands and into the Caribbean Sea).

Contents

Discovery and naming

Fish and molluscs have long been known from the Pebas Formation, however starting in 2002 systematic surveys of the Peruvian Iquitos area have led to the discovery of many vertebrate remains including further fish remains, mammals, turtles and an abundance of crocodilians, with two contemporaneous lignitic bonebeds preserving a minimum of 7 coexisting taxa. Among the fossils recovered from the Iquitos localities is the holotype of Gnatusuchus, MUSM 990, a nearly complete skull, as well as 3 referred specimens consisting of a right and two partial left mandibles. [2]

The name Gnatusuchus is a combination of the Quechua word "Ñatu", meaning small nose, and the Greek "Souchos" for crocodile. The species name pebasensis is based on the Pebas Formation, which gets its name from an old Amazonian village. [2]

Description

Gnatusuchus has a exceptionally short and rounded snout with a length-breadth index of 1.55, which is only slightly higher than the length-breadth index of the bizarre Notosuchian Simosuchus from the Late Cretaceous of Madagascar. The short cranium leads to the almost-circular orbits being located at the approximate midpoint of the skull and the nares are apple-shaped. Much like the cranium, the mandible is short and wide and ends in a short but massive retroarticular process. The overall shape of the mandible is shovel-like, which may have been adaptations for feeding on bivalves. [2]

Upper estimate of Gnatusuchus Gnatusuchus size.jpg
Upper estimate of Gnatusuchus

Gnatusuchus has highly reduced dentition compared to other blunt-snouted caimans, which typically possess 18 to 20 tooth alveoli, whereas Gnatusuchus has 14 teeth spread over the premaxilla and maxilla and 11 dentary teeth. The dentary teeth in particular can be separated into two groups with 7 anterior teeth and 4 "cheek teeth", the two groups separated by a diastema. Gnatusuchus exhibits a significant evolutionary loss of alveoli, with at least 3 alveoli being lost to create the diastema and further missing alveoli posterior to the 14th dentary tooth (while ancestral caimans would have possessed 4 to 6 more alveoli in that position). Besides the reduction of alveoli, Gnatusuchus also exhibits distinctly modified tooth morphology. The anterior most teeth are long and peg-like with blunt crowns. They are procumbent and shown apical wear. The posterior teeth meanwhile are globular shaped with a distinct neck. [2]

Based on the size of the skull material Salas-Gismondi et al. estimate a total body length of 148.9 to 167.7 centimetres (4.89 to 5.50 ft) depending on the proportions used for the calculation. The upper estimates are based on the American Alligator, while a smaller body length was recovered using the proportions of Morelet's Crocodile. [2]

Taxonomy

A phylogenetic analysis published alongside its initial description placed Gnatusuchus as the most basal member of the clade Caimaninae. Two other caimanines with crushing dentitions, Kuttanacaiman and Globidentosuchus , were also found to be basal caimanines, suggesting that a specialized crushing dentition was ancestral to the group. Later caimanines, including most modern species, have more generalized dentitions, although a few derived species such as C. wannlangstoni seem to have reacquired crushing teeth. Below is a cladogram from that analysis with crushing-type species in bold: [2]

Globidonta

Alligatorinae

Albertochampsa

Brachychampsa

Stangerochampsa

Caimaninae  (caimans)

Gnatusuchus pebasensis

Globidentosuchus brachyrostris

Eocaiman cavernensis

Kuttanacaiman iquitosensis

Purussaurus spp.

Mourasuchus spp.

Tsoabichi greenriverensis

Necrosuchus ionensis

Paleosuchus spp.

Jacarea

Centenariosuchus gilmorei

Caiman crocodilus

Caiman yacare

Caiman brevirostris

Caiman latirostris

Caiman wannlangstoni

La Venta caiman

Melanosuchus fisheri

Melanosuchus niger

Paleobiology

The Pebas Mega-Wetland System was created by the rise of the Andes during the beginning of the Neogene, eventually reaching an enormous size around of 1 million km2 during the middle Miocene. The wetlands consisted of a wide array of lakes, embayments, swamps and rivers that all drained into the Caribbean. The dysoxic marshes and swamps of the Pebas Formation were home to a great diversity of freshwater invertebrates (ostracods and molluscs) with a total of 85 co-occurring endemic species, most abundant of which being corbulid pachydontine bivalves. These bivalves possessed thick shells, profuse ornamentation and a series of other adaptations against predation. However, both successful and unsuccessful scaring caused by crushing predation can be found commonly in these bivalve fossils. This, alongside the specialised dentition and other adaptations of Gnatusuchus point to a durophagous diet in these caimans. Furthermore, the particular shape of Gnatusuchus may also point to its specific feeding strategy. Salas-Gismondi et al. hypothesize that Gnatusuchus used its jaw and procumbent teeth to "shovel" while crushing shells with the tightly packed posterior teeth. [2]

Gnatusuchus shared its environment with 2 other taxa of durophagous caimans, the basal Kuttanacaiman and Caiman wannlangstoni , a more derived caiman that independently developed crushing dentition. Besides these taxa with similar diets, the Pebas Mega-Wetlands were also shared by an unnamed species of Dwarf Caimain, the piscivorous, longirostrine gryposuchine Gryposuchus pachakamue , the gulp-feeding Mourasuchus atopus and the massive Purussaurus neivensis . [2]

Extinction

Strata directly overlying the ones Gnatusuchus was found in document the first decline in native mollusc diversity, caused by a marine incursion. Around 12 million years ago began the demise of the dysoxic lacustrine Pebas ecosystem following the continued uplift of the Andes splitting Proto-Amazonia into the modern river basins and the initiation of the transcontinental Amazon River drainage. The youngest records of Gnatusuchus were found in the Nueva Unión area south of Iquitos, however none of the other durophagous caimans of the Pebas Formation have been found there. Following the demise of the Pebas Mega-Wetlands, crushing caimans managed to persist into the Late Miocene in the Urumaco Formation while decreasing in diversity in the Solimões Formation of Acre. However Gnatusuchus itself has not been found in either formation. [2]

Related Research Articles

<i>Caiman</i> (genus) Genus of reptiles

Caiman is a genus of caimans within the alligatorid subfamily Caimaninae. They inhabit Central and South America. They are relatively small sized crocodilians, with all species reaching lengths of only a couple of meters and weighing 6 to 40 kg on average.

<i>Globidens</i> Extinct genus of lizards

Globidens is an extinct genus of mosasaur lizard classified as part of the Globidensini tribe in the Mosasaurinae subfamily.

<i>Mourasuchus</i> Extinct genus of reptiles

Mourasuchus is an extinct genus of giant, aberrant caiman from the Miocene of South America. Its skull has been described as duck-like, being broad, flat, and very elongate, superficially resembling Stomatosuchus from the Late Cretaceous.

Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil turtles, placodonts and invertebrates, as well as "bone-crushing" mammalian carnivores such as hyenas. Durophagy requires special adaptions, such as blunt, strong teeth and a heavy jaw. Bite force is necessary to overcome the physical constraints of consuming more durable prey and gain a competitive advantage over other organisms by gaining access to more diverse or exclusive food resources earlier in life. Those with greater bite forces require less time to consume certain prey items as a greater bite force can increase the net rate of energy intake when foraging and enhance fitness in durophagous species.

<i>Necrosuchus</i> Extinct genus of reptiles

Necrosuchus is an extinct genus of caiman from modern day Argentina that lived during the Paleocene epoch. It inhabited the fluvio-lacustrine environment of the Patagonian Salamanca Formation.

<i>Langstonia</i> Extinct species of reptile

Langstonia is an extinct genus of notosuchian crocodylomorph of the family Sebecidae. It lived in the middle Miocene, in the "Monkey Beds" of the Colombian Villavieja Formation. Langstonia was named in 2007 by Alfredo Paolillo and Omar Linares for fossils originally described by Langston in 1965 as Sebecus huilensis. Thus, the type species is L. huilensis.(Paolillo & Linares 2007)

<i>Gryposuchus</i> Extinct genus of gavialoid crocodilian

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. One recently described species, G. croizati, grew to an estimated length of 10 metres (33 ft). Gryposuchus is the type genus of the subfamily Gryposuchinae, although a 2018 study indicates that Gryposuchinae and Gryposuchus might be paraphyletic and rather an evolutionary grade towards the gharial.

<i>Pebasiconcha immanis</i> Extinct species of gastropod

Pebasiconcha immanis is an extinct species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Acavidae. The type locality of Pebasiconcha immanis is the Miocene Pebas Formation in the Colombian and Peruvian Amazonia.

Globidentosuchus is an extinct genus of basal caimanine crocodylian known from the late Middle to Late Miocene of the Middle and the Upper Members of the Urumaco Formation at Urumaco, Venezuela. Its skull was very short and robust, with large units of spherical teeth used to break the shells of molluscs as part of its durophagus diet. It is thought to be one of the most basal Caimanines, even sharing some traits with alligatorids.

<i>Chalawan</i> (genus) Extinct genus of reptiles

Chalawan is an extinct genus of pholidosaurid mesoeucrocodylian known from the Late Jurassic or Early Cretaceous Phu Kradung Formation of Nong Bua Lamphu Province, northeastern Thailand. It contains a single species, Chalawan thailandicus, with Chalawan shartegensis as a possible second species.

Pebas Formation Geological formation in Brazil, Colombia, Ecuador and Peru

The Pebas Formation is a lithostratigraphic unit of Miocene age, found in western Amazonia. The formation extends over 1,000,000 square kilometres (390,000 sq mi), including parts of Brazil, Peru, Ecuador and Colombia. It is interpreted as representing the deposits of a lake or series of lakes, formed within the foreland basin of the Andes mountain belt. It is known for its abundant fossil ostracods and molluscs and an unusually diverse group of crocodylians.

<i>Caiman wannlangstoni</i> Extinct species of reptile

Caiman wannlangstoni is an extinct species of caiman that lived in what is now the Amazon Basin and surrounding areas during the Middle and Late Miocene. Fossils of C. wannlangstoni have been found in the Pebas Formation near Iquitos in Peru and include partial skulls and isolated skull bones. Other fossils were uncovered from the Urumaco Formation in Venezuela and the Laventan Honda Group of Colombia. The species was first described in 2015. Features that in combination distinguish C. wannlangstoni from other caimans include a deep snout, a wavy upper jaw margin, a large and upward-directed narial opening, and blunt teeth at the back of the jaws. Based on the sizes of the skulls, its estimated body length is about 211 to 227 centimetres.

<i>Kuttanacaiman</i> Extinct genus of reptiles

Kuttanacaiman is a monotypic genus of extinct caiman represented by the type species Kuttanacaiman iquitosensis. Kuttanacaiman lived in what is now the Amazon basin during the Middle Miocene, approximately 13 million years ago (Ma). The species was named in 2015 on the basis of one nearly complete skull and a second partial skull from the Pebas Formation near Iquitos, Peru. K. iquitosensis is characterized by a short, rounded snout and blunt teeth at the back of its jaws that were likely adapted to crushing freshwater bivalves. Its estimated total body length is 171.2 to 189.1 centimetres.

Caiman brevirostris is an extinct species of caiman that lived during the Late Miocene, around 11.6 million years ago, to the end of the Miocene 5.3 million years ago in Acre and Amazonas, Brazil as well as Urumaco, Venezuela. Several specimens have been referred to the species, but only 3 of them are confidently placed in the species. C. brevirostris was originally named in 1987 on the basis of a single, incomplete rostrum with an associated mandibular ramus that had been found in Acre, Brazil. C. brevirostris is very distinct among Caiman species and caimaninae overall in that it preserves a characteristically short and robust skull that bears blunt posterior teeth that were built to break down harder foods. This was an adaption for durophagy, likely to crush shells of mollusks and clams which were common in the wetlands that C. brevirostris resided in.

Acresuchus is an extinct monospecific genus of large caiman from the Late Miocene of western Brazil and of Venezuela. The genus contains a single species, Acresuchus pachytemporalis. Acresuchus is a close relative of the giant caiman Purussaurus.

Ultrastenos is an extinct genus of Australian mekosuchine crocodilian first described in 2016. The type species Ultrastenos willisi was discovered at Riversleigh in northwestern Queensland, Australia, and lived during the Late Oligocene era.

<i>Kyhytysuka</i> Extinct marine reptile

Kyhytysuka is an extinct genus of ophthalmosaurian ichthyosaur from Early Cretaceous Colombia. The animal was previously assigned to the genus Platypterygius, but given its own genus in 2021. Kyhytysuka was a mid-sized ophthalmosaurian with heterodont dentition and several adaptations suggesting that it was a macropredatory vertebrate hunter living in shallow waters. It contains a single species, Kyhytysuka sachicarum.

<i>Monquirasaurus</i>

Monquirasaurus is a monotypic genus of giant pliosaurid from the Cretaceous Paja Formation in Colombia. It contains a single species, M. boyacensis, previously known as Kronosaurus boyacensis. It was a large animal, measuring 9.4 metres (31 ft) in length and 9.1 metric tons in body mass.

Pseudoprepotherium is an extinct genus of sloths in the family Mylodontidae. It was widespread across northern South America during the Middle and Upper Miocene around 21 to 5.3 million years ago. Fossil finds are known from Brazil Venezuela and Peru. Pseudoprepotherium lived in a tropical climate with a water-rich environment. The remains are limited to limb bones, with the exception of a few skulls and teeth. Based on this, it is a medium to large-sized mylodontid. The genus was described in 1961. Three species are known today, which were originally assigned to different genera.


Sacacosuchus is an extinct monospecific genus of marine gavialid that lived along the coast of the south-east Pacific from approximately 19 to 6.3 million years ago. Its fossils have been found in the Chilcatay and Pisco Formations of Peru, where it coexisted with the much larger Piscogavialis. Based on its skull, Sacacosuchus was most likely a generalist feeder with an estimated total body length of 4.32 m (14.2 ft). Its extinction is thought to have been caused by a combination of factors including falling sea levels and global cooling.

References

  1. Rio, Jonathan P.; Mannion, Philip D. (6 September 2021). "Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem". PeerJ . 9: e12094. doi: 10.7717/peerj.12094 . PMC   8428266 . PMID   34567843.
  2. 1 2 3 4 5 6 7 8 9 Salas-Gismondi, R.; Flynn, J. J.; Baby, P.; Tejada-Lara, J. V.; Wesselingh, F. P.; Antoine, P. -O. (2015). "A Miocene hyperdiverse crocodylian community reveals peculiar trophic dynamics in proto-Amazonian mega-wetlands". Proceedings of the Royal Society B: Biological Sciences. 282 (1804): 20142490. doi:10.1098/rspb.2014.2490. PMC   4375856 . PMID   25716785.