Acresuchus

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Acresuchus
Temporal range: Late Miocene, 11.62–5.33  Ma [1]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Clade: Archosauriformes
Order: Crocodilia
Family: Alligatoridae
Subfamily: Caimaninae
Clade: Jacarea
Genus: Acresuchus
Souza-Filho et al., 2018
Type species
Acresuchus pachytemporalis
Souza-Filho et al., 2018

Acresuchus ("Acre crocodile") is an extinct monospecific genus of medium-sized caiman from the Late Miocene of western Brazil and Venezuela. The genus contains a single species, Acresuchus pachytemporalis. Acresuchus is a close relative of the giant caiman Purussaurus.

Contents

Description

The hypodigm of Acresuchus consists of the holotype, UFAC-2507, a nearly complete skull, and several referred specimens, most found in Niteroi, located in the Solimões Formation in Acre. Acresuchus takes its name from the state it was found in (Acre), while the species name pachytemporalis refers to the extreme thickening of the squamosal bones in the holotype. [2] Another specimen, MCNUSB-PB-02FU-RS43, a skull fragment, was found in the middle member of the Urumaco Formation in Venezuela. [3]

According to the describing authors, Acresuchus is a "caimanine with a medium-sized body, teeth with smooth (non-serrated) carinae, orbits large in comparison with other caimanines, having roughly straight margins that are larger than the infratemporal fenestrae, circular external naris, posterior margin of the skull table transversely straight to slightly concave, posterolateral margin of squamosal upturned throughout the entire dorsal lateral margin with a dorsoventral expansion in the posterior portion of the eminence," with the last trait being a unique trait within the subfamily Caimaninae. [2]

The holotype of Acresuchus has an estimated skull length of 51.5 cm (20.3 in), smaller than all three species of Purussaurus, which suggests that Acresuchus may have represented a transitional form between the traditional caiman body plan and that of Purussaurus. Acresuchus lacked an enlarged external nostril, which in Purussaurus is hypothesized to reduce stress when biting, thus creating a more powerful bite. However, Acresuchus has small depressions in the posterior portions of the maxillae, similar to the deep excavations found in Purussaurus. These depressions may increase with body size in the Acresuchus-Purussaurus clade. [2]

Acresuchus shares traits with Purussaurus that may have been adaptations to large body size, such as large supratemporal fenestrae. These provided quicker capture of prey and better thermoregulation. [2]

A 2022 study estimated the body size of Acresuchus,Purussaurus, and another extinct caimanine, Mourasuchus using skull width and the dorsocranial length of the skull, determining that dorsocranial length is affected by changes in the skull throughout growth. Therefore, the authors used their estimates derived from skull width, estimating the length and mass of Acresuchus as 3.744 metres (12.28 ft) and 260.3 kilograms (574 lb), respectively, using ordinary least squares regression, while the estimates made utilizing a phylogenetic least squares regression recovered estimates of 3.401 metres (11.16 ft) and 225.6 kilograms (497 lb). The authors of the study acknowledged the lower results of the phylogenetic approach, stating that it may be due to a weaker correlation between skull width and body size compared to OLS. [4]

Classification

The describing authors of Acresuchus entered the data gleaned from its specimens into a phylogenetic analysis to test its affinities. The analysis found it to be a member of Caimaninae closely related to Purussaurus , [2] which was confirmed by subsequent studies. [1] The result of the initial analysis is shown in the cladogram below. [2]

Caimaninae

Culebrasuchus mesoamericanus

Gnatusuchus pebasensis

Globidentosuchus brachyrostris

Eocaiman palaeocenicus

Eocaiman itaboraiensis

Eocaiman cavernensis

Kuttanacaiman iquitosensis

Caiman gasparinae

Necrosuchus ionensis

Tsoabichi greenriverensis

Paleosuchus palpebrosus Smooth-fronted caiman

Paleosuchus trigonatus Cuvier's dwarf caiman

Mourasuchus pattersoni

Mourasuchus amazonensis

Mourasuchus atopus

Mourasuchus arendsi

Acresuchus pachytemporalis

Purussaurus neivensis

Purussaurus mirandai

Purussaurus brasiliensis

Centenariosuchus gilmorei

Jacarea

UCMP 39978

Melanosuchus fisheri

Melanosuchus niger Black caiman

Caiman wannlangstoni

Caiman brevirostris

Caiman latirostris Broad-snouted caiman

Caiman crocodilus Spectacled caiman

Caiman yacare Yacare caiman

Paleoecology

Acresuchus shares many features with the living black caiman, including size, which suggests it would have a similar diet. If this assumption is correct, juvenile Acresuchus would have preyed on small invertebrates, with adults feeding on fish and small to medium-sized mammals. The teeth at the back of the skull in Acresuchus are blunt, indicating that it may have also eaten hard-shelled animals. [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>Melanosuchus</i> Genus of caiman

Melanosuchus is a genus of caiman. The black caiman of South America is the sole extant (living) species, and is the largest living member of the subfamily Caimaninae, as well as the entire alligator family Alligatoridae.

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

Purussaurus is an extinct genus of giant caiman that lived in South America during the Miocene epoch, from the Friasian to the Huayquerian in the SALMA classification. It is known from skull material found in the Brazilian and Peruvian Amazon, Colombian Villavieja Formation, Panamanian Culebra Formation, Urumaco and Socorro Formations of northern Venezuela.

<i>Stupendemys</i> Extinct genus of turtles

Stupendemys is an extinct genus of freshwater side-necked turtle, belonging to the family Podocnemididae. It is the largest freshwater turtle known to have existed, with a carapace over 2 meters long. Its fossils have been found in northern South America, in rocks dating from the Middle Miocene to the very start of the Pliocene, about 13 to 5 million years ago. Male specimens are known to have possessed bony horns growing from the front edges of the shell and the discovery of the fossil of a young adult shows that the carapace of these turtles flattens with age. A fossil skull described in 2021 indicates that Stupendemys was a generalist feeder.

<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.

<i>Styracocephalus</i>

Styracocephalus platyrhynchus is an extinct genus of dinocephalian therapsid that existed during the mid-Permian throughout South Africa, but mainly in the Karoo Basin. It is often referred to by its single known species Styracocephalus platyrhynchus. The Dinocephalia clade consisted of the largest land vertebrates and herbivores during the early to mid-Permian. This period is often also referred to as the Guadalupian epoch, approximately 270 to 260 million years ago.

<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.

Bottosaurus is an extinct genus of alligatorid from the Late Cretaceous-Early Paleocene of New Jersey, Texas, and possibly North Carolina and South Carolina. Two species are currently accepted, with a third requiring re-evaluation.

<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.

Orthogenysuchus is an extinct genus of caimanine alligatorids. Fossils have been found from the Wasatch Beds of the Willwood Formation of Wyoming, deposited during the early Eocene. The type species is O. olseni. 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 indiscernible, making comparisons with other eusuchian material difficult.

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

Tsoabichi is an extinct genus of caimanine crocodylian. Fossils are known from the Green River Formation in Wyoming, and date back to the Ypresian stage of the Eocene. The genus was named and described in 2010 by paleontologist Christopher A. Brochu, with the type species being Tsoabichi greenriverensis. According to the current understanding of caiman evolutionary relationships, Tsoabichi is a basal member of Caimaninae and may have evolved after caimans dispersed into North America from northern and central South America, their main center of diversity in the Cenozoic.

Gryposuchinae is an extinct subfamily of gavialid crocodylians. Gryposuchines lived mainly in the Miocene of South America. However, "Ikanogavialis" papuensis may have 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, although a 2018 study indicates that the group might be paraphyletic and rather an evolutionary grade towards the gharial.

Culebrasuchus is an extinct, monotypic genus of caiman alligatorid known from the Early to Middle Miocene (Hemingfordian) of the Panama Canal Zone of Panama. It contains a single species, Culebrasuchus mesoamericanus.

Centenariosuchus is an extinct genus of caimanine crocodylian known from the Miocene of the Panama Canal Zone of Panama. It contains a single species, Centenariosuchus gilmorei, that was named in 2013 in honor of the upcoming centennial anniversary of the digging of the Panama Canal. Two fossil specimens consisting of skull fragments were found in the Early to Middle Miocene Cucaracha Formation in 2009 and 2011, and may belong to a single individual. The species is diagnosed by a combination of skull features that it shares with basal caimans like Tsoabichi, Eocaiman, Culebrasuchus, and the living genus Paleosuchus, as well as more derived caimans such as those in the genus Caiman. One feature that distinguishes Centenariosuchus from all other caimans is the straight outer margin of a hole on the underside of the skull called the suborbital fenestra. According to one phylogenetic analysis of caimanine relationships, Centenariosuchus falls within a clade or evolutionary grouping of caimans that includes the very large and highly specialized forms Purussaurus and Mourasuchus, known from the Miocene of South America.

<span class="mw-page-title-main">Jacarea</span> Clade of reptiles

Jacarea is a clade of caimans within the subfamily Caimaninae. Jacarea was first named by Norell in 1988 to include the extant species within the genera Caiman and Melanosuchus, while excluding the dwarf caiman genus Paleosuchus. In 1999, Brochu formally cladistically defined Jacarea as the last common ancestor of Caiman latirosris, Caiman crocodilus, Caiman yacare, Melanosuchus niger, and all its descendants. Molecular DNA phylogenetic studies recover Paleosuchus as outside of Jacarea, although morphological studies are inconsistent.

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>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>Gnatusuchus</i> Extinct genus of reptiles

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 Urumaco Formation is a formation in Venezuela that includes deposits from the Late Miocene. It is the site of several "giant forms": the turtles, crocodiles, sloths and rodents of Urumaco are among the largest of their groups.

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.

References

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  2. 1 2 3 4 5 6 7 Souza-Filho, Jonas P.; Souza, Rafael G.; Hsiou, Annie Schmaltz; Riff, Douglas; Guilherme, Edson; Negri, Francisco Ricardo; Cidade, Giovanne M. (2018-09-03). "A new caimanine (Crocodylia, Alligatoroidea) species from the Solimões Formation of Brazil and the phylogeny of Caimaninae". Journal of Vertebrate Paleontology. 38 (5): e1528450. Bibcode:2018JVPal..38E8450S. doi:10.1080/02724634.2018.1528450. ISSN   0272-4634. S2CID   91964360.
  3. Cidade, Giovanne M.; Rincón, Ascanio Daniel (October 2021). "The first occurrence of Acresuchus (Alligatoroidea, Caimaninae) from the Urumaco Formation of Venezuela and the late Miocene crocodylian fauna of northern South America". Journal of South American Earth Sciences. 110: 103344. Bibcode:2021JSAES.11003344C. doi:10.1016/j.jsames.2021.103344. ISSN   0895-9811.
  4. Paiva, Ana Laura S.; Godoy, Pedro L.; Souza, Ray B. B.; Klein, Wilfried; Hsiou, Annie S. (2022-10-01). "Body size estimation of Caimaninae specimens from the Miocene of South America". Journal of South American Earth Sciences. 118: 103970. Bibcode:2022JSAES.11803970P. doi: 10.1016/j.jsames.2022.103970 . ISSN   0895-9811. S2CID   251560425.