| Sacacosuchus | |
|---|---|
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Order: | Crocodilia |
| Family: | Gavialidae |
| Genus: | †Sacacosuchus Salas-Gismondiet al., 2022 |
| Species: | †S. cordovai |
| Binomial name | |
| †Sacacosuchus cordovai Salas-Gismondiet al.,2022 | |
Sacacosuchus is anextinctmonospecificgenus of marinegavialid that lived along the coast of the south-eastPacific from approximately 19 to 6.3 million years ago. Its fossils have been found in theChilcatay andPisco Formations ofPeru, where it coexisted with the much largerPiscogavialis. 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.[1]
Sacacosuchus is known from several adult to juvenile specimens mostly stemming from the Sacaco locality of thePisco Formation. Theholotype represents a nearly complete skull, while some of the referred specimens include partial skulls and dentary bones. Other material was found in theIca-Pisco Valley and the olderChilcatay Formation.[1]
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.[1]
Sacacosuchus was a medium-sizedgavialoid with a longirostrine skull as typical for the group. The transition from themaxilla to thepremaxilla is smooth, with the latter bone not expanding outward as in some other gavialids, including the modernIndian gharial. The margin of therostrum 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, howeverSacacosuchus 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 or the contemporaryPiscogavialis, instead more resembling the proportions ofthoracosaurs. Thenasal bone extends between the premaxillae and contacts the externalnares, 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 largestalveoli 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 theprefrontal bones,frontal bone andlacrimal bones are not raised. The skull table is more rectangular than it is circular with widesupratemporal fenestrae, whose border is overhung by the skull table. Towards the back, where the skull table is made up of thesquamosal, its surface slopes much like it does inGryposuchus andParatomistoma. When observing thepostorbital bar, it is slender andlanceolate in cross-section and facing to the front and sides. Thequadratojugal composes most of the lower boundary of theinfratemporal fenestra, but does not contact its posterior margin. Thedentary contained approximately seventeen to eighteen teeth. Thedentary symphysis extends to the ninth mandibular teeth where the bone contacts the deepsplenial symphysis.[1]
Size estimates suggest that thetype specimen ofSacacosuchus reached a length of up to 4.32 m (14.2 ft).[1]
Salas-Gismondi and colleagues conducted both Bayesian and maximum-parsimony analysis based on themorphological characteristics ofgavialoids to determine thephylogenetic position ofSacacosuchus. Their analysis recovered traditionaltomistomines asbasal members withinGavialoidea, withSacacosuchus nesting in a more derived position thanTomistoma, yet notably more basal thanPiscogavialis, which it shared its habitat with. It forms apolytomy alongside the also marineGavialosuchus (Europe),Thecachampsa (North America), and a large clade that contains most derived gavialids, including the bulk of South American forms. All this suggests thatSacacosuchus,Aktiogavialis andgryposuchines had independent origins.[1]
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During theMiocene, what is now thePisco Basin inPeru was largely covered by a shallowmarine transgression 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 andPiscogavialis, 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 variouscetaceans, seals, seabirds,marine sloths and sharks. As the Peruvian sediments yielded bones of both adults and juvenile specimens, it is assumed thatSacacosuchus spent its entire life in saltwater. AlthoughPiscogavialis 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.[1]
During the Miocene, environmental factors worked together to highly favor marinegavialoids, 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 asChile. However, despite these initially favorable conditions, global temperatures continuously dropped throughout the lateNeogene. Initially, bothSacacosuchus andPiscogavialis weren't heavily affected, with the water temperatures of their habitat continuing to support theseectotherms 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 theAndes Mountains, coupled with the more drastically dropping global temperatures of thePliocene.[1]
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