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| Sacacosuchus cordovai Salas-Gismondi, Ochoa, Jouve, Romero, Cardich, Perez, DeVries, Baby, Urbina & Carré, 2022 |
Abstract
The evolution of crocodylians as sea dwellers remains obscure because living representatives are basically freshwater inhabitants and fossil evidence lacks crucial aspects about crocodylian occupation of marine ecosystems. New fossils from marine deposits of Peru reveal that crocodylians were habitual coastal residents of the southeastern Pacific (SEP) for approximately 14 million years within the Miocene (ca 19 to 5 Ma), an epoch including the highest global peak of marine crocodylian diversity. The assemblage of the SEP comprised two long and slender-snouted (longirostrine) taxa of the Gavialidae: the giant Piscogavialis and a new early diverging species, Sacacosuchus cordovai. Although living gavialids (Gavialis and Tomistoma) are freshwater forms, this remarkable fossil record and a suite of evolutionary morphological analyses reveal that the whole evolution of marine crocodylians pertained to the gavialids and their stem relatives (Gavialoidea). This adaptive radiation produced two longirostrine ecomorphs with dissimilar trophic roles in seawaters and involved multiple transmarine dispersals to South America and most landmasses. Marine gavialoids were shallow sea dwellers, and their Cenozoic diversification was influenced by the availability of coastal habitats. Soon after the richness peak of the Miocene, gavialoid crocodylians disappeared from the sea, probably as part of the marine megafauna extinction of the Pliocene.
Keywords: Gavialoidea, longirostrine ecomorphs, biogeography, phylogenetics, marine crocodylians
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| Phylogenetic position of Sacacosuchus cordovai and other marine taxa (represented by their skulls) recovered within and outside the Crocodylia, with ancestral range reconstructions provided by S-DIVA. |
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| Photograph and schematic drawing of the skulls of Sacacosuchus cordovai gen. et sp. nov. from Sacaco at different ontogenetic stages. Adult specimen (holotype: MUSM 162) in dorsal (a), ventral (b), right lateral (e) and occipital (f) views. Sub-adult specimen (MUSM 161) in dorsal (c), ventral (d), left lateral (g; inverted) and occipital (h) views. Juvenile specimen (MUSM 160) in dorsal (i) view. ba, basioccipital; bs, basisphenoid; CH, choana; cq, cranioquadrate foramen; ec, ectopterygoid; ec.mx, maxilla surface for ectopterygoid; EN, external naris; eo, exoccipital; f, frontal; fcp, foramen carotideum posterior; IF, incisive foramen; ITF, infratemporal fenestra; j, jugal; j.la, lacrimal surface for jugal; j.mx, maxilla surface for jugal; l, lacrimal; ls, laterosphenoid; m5, m9, m14, maxillary tooth positions; mx, maxilla; n.pm, premaxilla surface for nasal; na, nasal; OR, orbit; p, parietal; pa, palatine; pa.mx, maxilla surface for palatine; pf, prefrontal; pm, premaxilla; p3, p4, premaxillary tooth positions; po, postorbital; pt, pterygoid; q, quadrate; qj, quadratojugal; qj.q, quadrate surface for quadratojugal; s, shelf; so, supraoccipital; sq, squamosal; STF, supratemporal fenestra; SOF, suborbital fenestra; v, foramen vagus; xii, foramen for hypoglossal nerve. All photographs to the same scale. Scale bar equals 5 cm. |
Crocodyliformes Hay, 1930
Crocodylia Gmelin, 1789
Longirostres (Cuvier, 1807)
Gavialidae (Adams, 1854)
Sacacosuchus cordovai gen. et sp. nov.
Etymology: Sacaco after the rich fossiliferous area from where most remains were found; cordovai after colleague and Prof. Jesús Córdova, to honour his brave and unconditional support to develop palaeontology in Peru.
Rodolfo Salas-Gismondi, Diana Ochoa, Stephane Jouve, Pedro E. Romero, Jorge Cardich, Alexander Perez, Thomas DeVries, Patrice Baby, Mario Urbina and Matthieu Carré. 2022. Miocene Fossils from the southeastern Pacific shed light on the last Radiation of Marine Crocodylians. Proc. R. Soc. B. 289: 20220380. DOI: 10.1098/rspb.2022.0380
