''Sacacosuchus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

monospecific In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of marine

gavialid Gavialidae is a family of large semiaquatic crocodilians with elongated, narrow snouts. Gavialidae consists of two living species, the gharial (''Gavialis gangeticus'') and the false gharial (''Tomistoma schlegelii''), both occurring in Asia. Man ...

that lived along the coast of the south-east

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

from approximately 19 to 6.3 million years ago. Its fossils have been found in the Chilcatay and

Pisco Formation The Pisco Formation is a geologic formation located in Peru, on the southern coastal desert of Ica, Peru, Ica and Arequipa. The approximately thick formation was deposited in the Pisco Basin, spanning an age from the Miocene, Middle Miocene up to ...

s of

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...

, where it coexisted with the much larger ''

Piscogavialis ''Piscogavialis'' is an extinct monospecific genus of gryposuchine gavialid crocodylian. The only species yet known is ''P. jugaliperforatus''. Fossils of ''Piscogavialis'' have been found from the Mio-Pliocene Pisco Formation of the Sacaco Bas ...

''. Based on its skull, ''Sacacosuchus'' was most likely a generalist feeder with an estimated total body length of . Its extinction is thought to have been caused by a combination of factors including falling sea levels and global cooling.

History and naming

''Sacacosuchus'' is known from several adult to juvenile specimens mostly stemming from the Sacaco locality of the

. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

represents a nearly complete skull, while some of the referred specimens include partial skulls and dentary bones. Other material was found in the Ica-Pisco Valley and the older Chilcatay Formation. The generic name derives from the Sacaco area of the Pisco Basin and the Greek "suchus" meaning crocodile. The species name honors professor Jesús Córdova for his work on the paleontology of Peru.

Description

''Sacacosuchus'' was a medium-sized

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 ...

with a longirostrine skull as typical for the group. The transition from the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

to the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

is smooth, with the latter bone not expanding outward as in some other gavialids, including the modern Indian gharial. The margin of the

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

remains parallel without notable constrictions that would give it a wavy appearance, however it does expand gradually towards the orbital region. The tooth row itself is however slightly sinuous and the rostrum appears to curve slightly upwards in sideview. The proportions between the rostrum and the total skull length is similar to that of modern gharials, however ''Sacacosuchus'' differs more significantly in the relative width of the skull. The difference in width between the rostrum and the skull behind the eyes is notably less drastic in this genus than it is in Indian gharials, ''

Tomistoma ''Tomistoma'' is a genus of gavialid crocodilians. They are noted for their long narrow snouts used to catch fish, similar to the gharial. ''Tomistoma'' contains one extant (living) member, the false gharial (''Tomistoma schlegelii''), as we ...

'' or the contemporary ''

'', instead more resembling the proportions of thoracosaurs. The

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...

extends between the premaxillae and contacts the external nares, which open dorsally and resemble an elongated heart. Each premaxilla contains five teeth followed by fourteen maxillary teeth, the fifth as well as the ninth to twelfth of which being enlarged. The ninth to twelfth are the largest

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * ...

in the skull. The orbits are enlarged and circular in shape with a low-set ventral margin which is barrel vault-shaped. Unlike many modern crocodiles, the edges or the orbits which are formed by the

prefrontal bones The prefrontal bone is a bone separating the lacrimal and frontal bones in many tetrapod skulls. It first evolved in the sarcopterygian clade Rhipidistia, which includes lungfish and the Tetrapodomorpha. The prefrontal is found in most modern and ...

frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, par ...

and

lacrimal bones The lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders. Several bony landmarks of ...

are not raised. The skull table is more rectangular than it is circular with wide

supratemporal fenestrae The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

, whose border is overhung by the skull table. Towards the back, where the skull table is made up of the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal The quadratojugal is a skull bone present in many vertebrates, including ...

, its surface slopes much like it does in ''

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 ''

Paratomistoma ''Paratomistoma'' (meaning "next to or near ''Tomistoma''") is an extinct monospecific genus of gavialoid crocodylian. It is based on the holotype specimen CGM 42188, a partial posterior skull and lower jaw discovered at Wadi Hitan, Egypt ...

''. When observing the

postorbital bar The postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch, which runs laterally around the eye socket. It is a trait that only occurs in mammalian taxa, such as most streps ...

, it is slender and

lanceolate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular o ...

in cross-section and facing to the front and sides. The

quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

composes most of the lower boundary of the

infratemporal fenestra An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets, ...

, but does not contact its posterior margin. The

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

contained approximately seventeen to eighteen teeth. The dentary symphysis extends to the ninth mandibular teeth where the bone contacts the deep

splenial The splenial is a small bone in the lower jaw of reptiles, amphibians and birds, usually located on the lingual side (closest to the tongue) between the angular and surangular The suprangular or surangular is a jaw bone found in most land verteb ...

symphysis. Size estimates suggest that the

type specimen In biology, a type is a particular wiktionary:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to a ...

of ''Sacacosuchus'' reached a length of up to .

Phylogeny

Salas-Gismondi and colleagues conducted both Bayesian and maximum-parsimony analysis based on the morphological characteristics of

s to determine the

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

position of ''Sacacosuchus''. Their analysis recovered traditional tomistomines as basal members within

Gavialoidea 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 ...

, with ''Sacacosuchus'' nesting in a more derived position than ''

'', yet notably more basal than ''

'', which it shared its habitat with. It forms a

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...

alongside the also marine ''

Gavialosuchus ''Gavialosuchus'' is an extinct genus of gavialid crocodylian from the early Miocene of Europe. Currently only one species is recognized, as a few other species of ''Gavialosuchus'' have since been reclassified to other genera. Taxonomy The typ ...

'' (Europe), ''

Thecachampsa ''Thecachampsa'' is an extinct genus of gavialoid crocodylian, traditionally regarded as a member of the subfamily Tomistominae. Fossils have been found from the eastern United States in deposits of Miocene age. Those named in the 19th century we ...

'' (North America), and a large clade that contains most derived gavialids, including the bulk of South American forms. All this suggests that ''Sacacosuchus'', ''

Aktiogavialis ''Aktiogavialis'' is an extinct genus of crocodylian that lived from the Oligocene until the Miocene in what is now the Caribbean. Two species have been described: ''Aktiogavialis puertoricensis'' from the Middle Oligocene of Puerto Rico and ''Ak ...

'' and gryposuchines had independent origins.

Paleobiology

During the

Miocene The Miocene ( ) is the first 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 means "less recen ...

, what is now the

Pisco Basin Pisco Basin ( es, Cuenca de Pisco) is a sedimentary basin extending over in southwestern Peru.Solís Mundaca, 2018, p.1 The basin has a thick sedimentary fill, which is about half the thickness of more northern foreland basins in Peru. The old ...

was largely covered by a shallow

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

that connected to the open ocean. The environment was marked by shallow waters, protected bays with rocky shores and small islands. The south-east Pacific coast was inhabited by at least two species of crocodilians, ''Sacacosuchus'' and ''

'', throughout most of this time period. The remains of both species were found alongside other animals typical for the marine environments of this region including various

cetacea Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

ns, seals, seabirds, marine sloths and sharks. As the Peruvian sediments yielded bones of both adults and juvenile specimens, it is assumed that ''Sacacosuchus'' spent its entire life in saltwater. Although ''Piscogavialis'' was notably larger, it was also likely more specialized, feeding primarily on fast fish. ''Sacacosuchus'', meanwhile, in spite of being only half the length of its contemporary relative, was adapted to a more generalist diet. During the Miocene, environmental factors worked together to highly favor marine

s, in particular warm temperatures and abundant shallow water coastal environments suited to their lifestyle. Subsequently, their diversity was high during most of this time period with their range extending as far south as

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. However, despite these initially favorable conditions, global temperatures continuously dropped throughout the late

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...

. Initially, both ''Sacacosuchus'' and ''Piscogavialis'' weren't heavily affected, with the water temperatures of their habitat continuing to support these

ectotherm An ectotherm (from the Greek () "outside" and () "heat") is an organism in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature.Davenport, John. Animal Life a ...

s until at least the end of the Miocene period. Eventually, however, the extinction of Peru's marine gavialids was brought on by the disruption of these coastal ecosystems, caused by dropping sea levels and the uplifting of the

Andes Mountains The Andes, Andes Mountains or Andean Mountains (; ) are the List of mountain ranges#Mountain ranges by length, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range i ...

, coupled with the more drastically dropping global temperatures of the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58

References

{{Extinct Crocodilia, T. Gavialidae Prehistoric crocodylomorphs Miocene crocodylomorphs Neogene Peru Fossils of Peru Huayquerian Chasicoan Mayoan Laventan Colloncuran Friasian Santacrucian Colhuehuapian Miocene South America Fossil taxa described in 2022