''Sacacosuchus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce 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 "unispe ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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 the definition, to Antarctica in the south, and is bounded by the cont ...

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, Late Miocene up to t ...

s of

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

, where it coexisted with the much larger ''

Piscogavialis ''Piscogavialis'' is an extinct monospecific genus of Gryposuchinae, gryposuchine Gavialidae, gavialid crocodylian. The only species yet known is ''P. jugaliperforatus''. Fossils of ''Piscogavialis'' have been found from the Miocene, Mio-Pliocene ...

''. 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 (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

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 Chilcatay Formation is a geologic formation located in Peru. The formation was deposited in the Pisco Basin, during the Early Miocene, roughly from 19.2 to 18.0 Ma. Fossil remains of baleen whales, sharks, and rays Ray or RAY may refer to: ...

. 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 In vertebrates, the maxilla (: maxillae ) 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 two maxil ...

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 mammals h ...

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 ** podium * 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 ...

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 well ...

'' 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 * M ...

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 In the human skull, the frontal bone or sincipital bone is an unpaired bone which consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bo ...

and

lacrimal bones The term Lacrimal or lachrymal, may refer to: Anatomy * Lacrimal apparatus * Lacrimal artery * Lacrimal bone * Lacrimal canaliculi (singular: canaliculus), also known as ''Lacrimal ducts'' * Lacrimal fossa (disambiguation) * Lacrimal fluid, see ...

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

supratemporal fenestrae Temporal fenestrae are openings in the Temple (anatomy), temporal region of the skull of some Amniote, amniotes, behind the Orbit (anatomy), orbit (eye socket). These openings have historically been used to track the evolution and affinities of re ...

, 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 bones form the cheek series of the skull. The bone forms an ancestra ...

, 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, Egyp ...

''. 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 strep ...

, it is slender and

lanceolate The following terms are used to describe leaf plant morphology, morphology in the description and taxonomy (biology), taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade ...

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 Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit (eye socket). These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly (al ...

, but does not contact its posterior margin. The

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

contained approximately seventeen to eighteen teeth. The

dentary symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral halve ...

extends to the ninth mandibular teeth where the bone contacts the deep

splenial The splenial is a small bone in the lower jaw of reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology ...

symphysis. Size estimates suggest that the

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

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 () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

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

Gavialoidea Gavialoidea is one of three superfamily (zoology), 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 ''Tomi ...

, 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 tree ...

alongside the also marine '' Gavialosuchus'' (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 The Caribbean ( , ; ; ; ) is a region in the middle of the Americas centered around the Caribbean Sea in the A ...

'' and gryposuchines had independent origins.

Paleobiology

During the

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

, what is now the

Pisco Basin Pisco Basin () is a sedimentary basin extending over in southwestern Peru.Solís Mundaca, 2018, p.1 The basin has a 2-kilometre (1.25-mile) thick sedimentary fill, which is about half the thickness of more northern foreland basins in Peru. The o ...

was largely covered by a shallow

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

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 belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

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 western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

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

Neogene The Neogene ( ,) 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 million years ago. It is the second period of th ...

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

ectotherm An ectotherm (), more commonly referred to as a "cold-blooded animal", is an animal in which internal physiological sources of heat, such as blood, are of relatively small or of quite negligible importance in controlling body temperature.Dav ...

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 Mountain Range (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long and wide (widest between 18°S ...

, coupled with the more drastically dropping global temperatures of the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58

References

{{Taxonbar, from=Q111972856, from2=Q111972860 Gavialidae Miocene crocodylomorphs Neogene Peru Fossils of Peru Huayquerian Chasicoan Mayoan Laventan Colloncuran Friasian Santacrucian Colhuehuapian Miocene reptiles of South America Fossil taxa described in 2022