Necrosuchus

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Necrosuchus
Temporal range: Paleocene (Peligran),
61.6–59.2  Ma [1]
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Necrosuchus ionensis.jpg
Artist's restoration
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Alligatoridae
Subfamily: Caimaninae
Clade: Jacarea
Genus: Necrosuchus
Simpson, 1937 [2]
Type species
Necrosuchus ionensis
Simpson, 1937

Necrosuchus is an extinct genus of caiman from modern day Argentina that lived during the Paleocene epoch (Selandian age, about 60 million years ago). It inhabited the fluvio-lacustrine environment of the Patagonian Salamanca Formation. [3] [4]

Contents

History and naming

The fossil remains of Necrosuchus were unearthed on April 3, 1931 during the First Scarritt Expedition in the Argentinian Salamanca Formation and presented to American paleontologist Charles C. Mook. Mook however, busy with other research, was unable to describe the specimen himself. As an initial description was deemed vital to the works of several student researches at the time, Mook handed the specimen back to George G. Simpson for study. He eventually published his preliminary description in 1937, writing that his research "only carries this study as far as necessary" in the hopes of a more detailed description being later published by Mook himself. However this would not come to be and the postcranial was not described until 2012. [4] Holotype AMNH 3219 consists of much of the postcranial anatomy alongside a right dentary and assorted cranial fragments not recognized as such in 1937. [2] Although other material from Paleocene Patagonia shares similarities with Necrosuchus, none of it can be safely referred to the genus itself. [4]

Simpson explains the meaning of the generic name as being a compound word of "nekros" meaning "dead," and "suchus" meaning crocodile. Simpson described how "a well-meaning lady asked us if it were dead", which inspired his choice of name. The specific name refers to the Las Violetas site: ion is "violet" in Latin. [2]

Description

The dentary teeth of Necrosuchus are more or less evenly spaced throughout the holotype, only the 12th and 13th teeth lying closer together than the others (however even then without being in direct contact). The upper margin of the jaw is notably concave between the 1st and 4th tooth and between the 4th and 13th, after which it remains straight. The teeth show very little differentiation from one another in morphology, however the difference in tooth size is striking and almost equal in its degree to that of extant genus Caiman . Although the degree of enlargement is similar, the distribution is not the same and more similar to that seen in Leidyosuchus (many of the species used for comparison being now considered Borealosuchus ) according to Simpson. The first two teeth are of the same size, followed by a decrease in size for tooth three. The 4th dentary tooth is the largest of the lower jaw and followed by a series of noticeably smaller teeth (a similar condition is seen in extant caimans). Unlike in extant taxa however, the 13th tooth is enlarged to the point that it almost rivals the 4th dentary tooth in size, and the transition in size before and after it is much less abrupt. [2] The 13th tooth's status of second largerst tooth in the dentary differentiates Necrosuchus from all other caimans other than Purussaurus brasiliensis and some species of Paleosuchus . Necrosuchus differs from Purussaurus through its slender mandibular ramus as well as the size of the first four dentary and from Paleosuchus through the anatomy of the atlantal ribs and the lack of mediolaterall compression on the posterior dentary teeth. [5]

The postcranial remains include 4 dorsal vertebrae that were preserved in articulation. They are procoelous with rectangular neural spines and lacking their transverse processes due to preservation. At some point in the past, the vertebrae had been identified as dorsals 5 to 8, but the basis for this assignment is not known. However, the study by Brochu confirms that this assumption was correct based on the anatomy of the hypapophyseal keel. The last two dorsals are also preserved in articulation with the sacral vertebrae. The sutures of the dorsal and sacral neurocentrals are unfused and still open, suggesting that the animal was not yet fully grown by the time of its death. The pectoral girdle is largely preserved, with parts of both scapula coracoids (missing the scapula blade), both humeri, ulnae and radii as well as one radiale. They largely resemble forelimbs of modern crocodilians. Both pelvic girdles are preserved, although one of the ilia is distorted, but the corresponding bone of the other side preserves its natural state. The blades of the pubis are less symmetrical than in modern crocs. The hindlimbs preserve the femur, tibia, parts of the fibula and various foot bones. Osteoderms were preserved but not in articulation. [4]

Phylogeny

Early analysis of Necrosuchus believed it to be a close relative of Leidyosuchus , which at the time was believed to be a crocodylid. Later research showed that Necrosuchus shows derived features of alligatoroids and more precisely caimanines. By the time Brochu described the postcrania of Necrosuchus, many species of Leidyosuchus originally used for comparison were reclassified as species of Borealosuchus . The postcranial material however differs significantly from Borealosuchus and shows further affinities with caimans. [4] Following a taxonomic revision and amended diagnosis published in 2020, Cicade and colleagues recovered Necrosuchus as a derived member of Caimaninae nested within a large polytomy with most extant non- paleosuchus caimans and Purussaurus . This polytomy was a direct result of the inclusion of Necrosuchus and Centenariosuchus , and their removal resulted in a better resolved phylogenetic tree. Following a Pcr Prune analysis, two alternative placements of Necrosuchus recover it as either basal to the clade Jacarea or as basal to a clade comprising Jacarea and Acresuchus + Purussaurus . [5] The below cladogram shows the results of the strict consensus phylogenetic analysis. [5]

Caimaninae

Culebrasuchus mesoamericanus

Gnatusuchus pebasensis

Globidentosuchus brachyrostris

Eocaiman palaeocenicus

Eocaiman itaboraiensis

Eocaiman cavernensis

Kuttanacaiman iquitosensis

Bottosaurus harlani

Tsoabichi greenriverensis

Paleosuchus trigonatus

Paleosuchus palpebrosus

Caiman gasparinae

Mourasuchus amazonensis

Mourasuchus pattersoni

Mourasuchus atopus

Mourasuchus arendsi

Jacarea

Necrosuchus ionensis

UCMP 39978

Caiman wannlangstoni

Centenariosuchus gilmorei

Caiman brevirostris

Melanosuchus niger

Caiman latirostris

Caiman yacare

Caiman crocodilus

Acresuchus pachytemporalis

Purussaurus neivensis

Purussaurus mirandai

Purussaurus brasiliensis

The following morphological phylogenetic cladogram published by Rio and colleagues recovered a more resolved tree, with Necrosuchus clading alongside Bottosaurus from Cretaceous-Paleocene North America and Protocaiman , also from the Salamanca Formation. [1]

Caimaninae

Ceratosuchus burdoschi

Wannaganosuchus brachymanus

Stangerochampsa mccabei

Brachychampsa montana

Gnatusuchus pebasensis

Kuttanacaiman iquitosensis

Globidentosuchus brachyrostris

Caiman lutescens

Caiman gasparinae

Mourasuchus atopus

Mourasuchus arendsi

Mourasuchus amazonensis

Jacarea

Caiman yacare

Acresuchus pachytemporalis

Purussaurus neivensis

Purussaurus mirandai

Purussaurus brasiliensis

Caiman wannlangstoni

UCMP 39978

Melanosuchus niger

Caiman brevirostris

Caiman latirostris

Protocaiman peligrensis

Necrosuchus ionensis

Bottosaurus harlani

Caiman crocodilus

Tsoabichi greenriverensis

Paleosuchus trigonatus

Paleosuchus palpebrosus

Related Research Articles

<span class="mw-page-title-main">Alligatoridae</span> Family of crocodilians including alligators, caimans and kin

The family Alligatoridae of crocodylians includes alligators, caimans and their extinct relatives.

<span class="mw-page-title-main">Cuvier's dwarf caiman</span> Species of reptile

Cuvier's dwarf caiman is a small crocodilian in the alligator family from northern and central South America. It is found in Brazil, Bolivia, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, Trinidad and Venezuela. It lives in riverine forests, flooded forests near lakes, and near fast-flowing rivers and streams. It can traverse dry land to reach temporary pools and tolerates colder water than other species of caimans. Other common names for this species include the musky caiman, the dwarf caiman, Cuvier's caiman, and the smooth-fronted caiman. It is sometimes kept in captivity as a pet and may be referred to as the wedge-head caiman by the pet trade community.

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

Mahajangasuchus is an extinct genus of crocodyliform which had blunt, conical teeth. The type species, M. insignis, lived during the Late Cretaceous; its fossils have been found in the Maevarano Formation in northern Madagascar. It was a fairly large predator, measuring up to 4 metres (13 ft) long.

<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.

Wannaganosuchus is an extinct genus of small alligatorid crocodylian. It was found in Late Paleocene-age rocks of Billings County, North Dakota, United States.

Procaimanoidea is an extinct genus of alligatorid from the Eocene of North America. It was named posthumously in 1946 by Charles W. Gilmore; the type species is P. utahensis, from the Uintan of Utah. It is based on USNM 15996, a nearly complete skull and partial left hind leg. A second species, P. kayi, was named in 1941 by C.C. Mook as a species of Hassiacosuchus, for remains from the Bridgerian of Wyoming. It was reassigned to Procaimanoidea in 1967 by Wassersug and Hecht.

<span class="mw-page-title-main">Caiman</span> Subfamily of reptiles

A caiman is an alligatorid belonging to the subfamily Caimaninae, one of two primary lineages within the Alligatoridae family, the other being alligators. Caimans inhabit Mexico, Central and South America from marshes and swamps to mangrove rivers and lakes. They have scaly skin and live a fairly nocturnal existence. They are relatively small-sized crocodilians with an average maximum weight of 6 to 40 kg depending on species, with the exception of the black caiman, which can grow more than 4 m (13 ft) in length and weigh in excess of 1,000 kg. The black caiman is the largest caiman species in the world and is found in the slow-moving rivers and lakes that surround the Amazon basin. The smallest species is the Cuvier's dwarf caiman, which grows to 1.2 to 1.5 m long. There are six different species of caiman found throughout the watery jungle habitats of Central and Southern America. The average length for most of the other caiman species is about 2 to 2.5 m long.

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

Allognathosuchus is an extinct genus of alligatorine crocodylian with a complicated taxonomic history. It was named in 1921.

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.

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.

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

Globidonta is a clade of alligatoroids that includes alligators, caimans, and closely related extinct forms. It is defined as a stem-based clade including Alligator mississippiensis and all forms more closely related to it than to Diplocynodon. The group's fossil range extends back into the Late Cretaceous with early alligatoroids such as Albertochampsa and Brachychampsa. Extinct globidontans were particularly common in North America and Eurasia, and their modern range also includes South America.

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.

<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>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.

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 medium-sized caiman from the Late Miocene of western Brazil andVenezuela. The genus contains a single species, Acresuchus pachytemporalis. Acresuchus is a close relative of the giant caiman Purussaurus.

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

Chinatichampsus is an extinct genus of crocodilian from the Devil's Graveyard Formation of Texas, specifically the Dalquest Desert Research Site. It is a monotypic genus, containing only the type species Chintanichampsus wilsonorum. A single specimen, TMM 45911–1, was first discovered in 2010. Chinatichampsus is the most basal Eocene caimanine, dating to between 42.8 and 41.5 million years ago, and is considered to be more basal than Protocaiman.

Barrosasuchus is a genus of peirosaurid notosuchian from the Santonian of Argentina and part of the extensive peirosaurid record of Late Cretaceous Patagonia. It contains one species, Barrosasuchus neuquenianus. B. neuquenianus is known from an almost complete skull and the majority of the articulated postcranial skeleton, making it the best preserved Patagonian peirosaurid.

References

  1. 1 2 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 Simpson, George Gaylord (1937). "An ancient eusuchian crocodile from Patagonia" (PDF). American Museum Novitates (965): 1–20.
  3. "†Necrosuchus Simpson 1937". Paleobiology Database. Fossilworks. Retrieved 17 December 2021.
  4. 1 2 3 4 5 Brochu, C.A. (2012). "Phylogenetic relationships of Necrosuchus ionensis Simpson, 1937 and the early history of caimanines". Zoological Journal of the Linnean Society. 163: S228–S256. doi: 10.1111/j.1096-3642.2011.00716.x .
  5. 1 2 3 Cicade, G.M.; Fortier, D.; Hsiou, A.S. (2020). "Taxonomic and phylogenetic review of Necrosuchus ionensis (Alligatoroidea: Caimaninae) and the early evolution and radiation of caimanines". Zoological Journal of the Linnean Society. 189 (2): 657–669. doi: 10.1093/zoolinnean/zlz051 .