Piscogavialis

Piscogavialis Temporal range: Late Miocene, 11.6–5.3 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
Skull
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauromorpha
Clade:	Archosauriformes
Order:	Crocodilia
Family:	Gavialidae
Subfamily:	†Gryposuchinae
Genus:	†Piscogavialis Kraus 1998
Type species
†Piscogavialis jugaliperforatus Kraus 1998

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 Basin in southern Peru in 1998,^[2] where it coexisted with the much smaller gavialid Sacacosuchus.^[3]

Piscogavialis is known only from a single specimen, but it represents some of the best preserved gavialid material known from South America. The skull is preserved in three dimensions and is nearly complete. A mandible and some postcranial material have also been found in association with the skull. Several important features of the occipital region of the skull support a referral to the family Gavialidae, which also includes the extant gharial and false gharial.

Paleobiology

The strata from which remains of Piscogavialis have been found suggest that it lived in a coastal environment.^[4][5] Another extinct marine gavialid, Sacacosuchus, was described in 2022 and discovered in the same formation. Sacacosuchus was smaller, estimated to be up to 4.32 m (14.2 ft) long, whereas Piscogavialis was nearly double the size.^[3]

During the Miocene, what is now the Pisco Basin in Peru was largely covered by a shallow marine 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, Piscogavialis and Sacacosuchus, 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 cetaceans, 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.^[3]

During the Miocene, environmental factors worked together to highly favor marine gavialoids, 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. However, despite these initially favorable conditions, global temperatures continuously dropped throughout the late Neogene. Initially, both Piscogavialis and Sacacosuchus weren't heavily affected, with the water temperatures of their habitat continuing to support these ectotherms 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, coupled with the more drastically dropping global temperatures of the Pliocene.^[3]

Phylogeny

A phylogenetic analysis conducted in a 2007 study found Gryposuchinae to include the genera Aktiogavialis, Gryposuchus, Ikanogavialis, Piscogavialis, and Siquisiquesuchus. Below is a cladogram from the 2007 analysis showing the phylogenetic relationships of gryposuchines among gavialoids:^[5]

Gavialoidea	Eothoracosaurus Thoracosaurus Eosuchus Argochampsa Gavialidae  Eogavialis Gavialis Gryposuchinae  Ikanogavialis Piscogavialis Siquisiquesuchus Gryposuchus Aktiogavialis

Alternatively, a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data indicated that the members of Gryposuchinae may in fact be paraphyletic and rather an evolutionary grade towards Gavialis and the gharial, as shown in the cladogram below:^[6]

Gavialidae	Gavialis gangeticus Gharial Gavialis bengawanicus† Gavialis browni† Gryposuchus colombianus† Ikanogavialis† Gryposuchus pachakamue† Piscogavialis† Harpacochampsa† Toyotamaphimeia† Penghusuchus† Gavialosuchus† Tomistoma lusitanicum† Tomistoma schlegelii False gharial	Gryposuchinae

The below cladogram is from the 2022 Salas-Gismondi et al. study describing the newly discovered co-existing Sacacosuchus, and shows Piscogavialis as a more derived member of Gavialidae:^[3]

Crocodyloidea Gavialoidea †Kentisuchus spenceri †Dollosuchoides densmorei †Maroccosuchus zennaroi †Maomingosuchus petrolica Gavialidae Tomistoma schlegelii, false gharial †Tomistoma lusitanicum †Gavialosuchus eggenburgensis †Sacacosuchus cordovai †Thecachampsa antiqua †Thecachampsa carolinensis †Thecachampsa americana †Tomistoma dowsoni †Tomistoma coppensi †Tomistoma cairense †Paratomistoma courti †MUSM 1513 †Argochampsa krebsi †Aktiogavialis caribesi †Aktiogavialis puertoricensis †Eogavialis †Gavialis bengawanicus Gavialis gangeticus, gharial †Siwalik Gavialis †Siquisiquesuchus venezuelensis †Piscogavialis jugaliperforatus †Ikanogavialis gameroi †Dadagavialis gunai †Gryposuchus pachakamue †Gryposuchus neogaeus †Gryposuchus croizati †Gryposuchus colombianus

References

1. 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. Piscogavialis at Fossilworks.org
3. Salas-Gismondi, R.; Ochoa, D.; Jouve, S.; Romero, P.E.; Cardich, J.; Perez, A.; DeVries, T.; Baby, P.; Urbina, M.; Carré, M. (2022-05-11). "Miocene fossils from the southeastern Pacific shed light on the last radiation of marine crocodylians". Proceedings of the Royal Society B. 289. doi:10.1098/rspb.2022.0380. PMC 9091840.
4. Kraus, R. M. (1998). "The cranium of Piscogavialis jugaliperforatus n.gen., n.sp. (Gavialidae, Crocodylia) from the Miocene of Peru". Paläontologische Zeitschrift. 72 (3): 389–406. doi:10.1007/bf02988368. S2CID 84214781.
5. Vélez-Juarbe, J.; Brochu, C. A.; Santos, H. (2007). "A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile". Proceedings of the Royal Society B. 274 (1615): 1245–1254. doi:10.1098/rspb.2006.0455. PMC 2176176. PMID 17341454.
6. Michael S. Y. Lee; Adam M. Yates (27 June 2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil". Proceedings of the Royal Society B. 285 (1881). doi:10.1098/rspb.2018.1071. PMC 6030529. PMID 30051855.