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| Kostensuchus atrox Novas, Pol, Agnolín, Carvalho, Manabe, Tsuihiji, Rozadilla, Lio & Isasi, 2025 |
Abstract
The first crocodyliform specimen from the Maastrichtian Chorrillo Formation (Austral Basin, Patagonia) is here described. The discovery was made about 30 km to the SW of the town of El Calafate (Province of Santa Cruz, Argentina) and consists of a beautifully preserved and articulated skull and jaws, and part of the postcranial skeleton that were preserved encased in a large concretion. This new taxon belongs to the notosuchian clade Peirosauridae, representing the latest and southernmost record for this group of crocodyliforms. The new taxon is recovered as closely related to other robust and broad-snouted peirosaurids that lived by the end of the Cretaceous Period, such as Colhuehuapisuchus from the Maastrichtian of Central Patagonia and Miadanasuchus oblita from the Maastrichtian of Madagascar. The completeness of the new specimen reveals, for the first time, the anatomy and body plan of a large and broad snouted peirosaurid. The new taxon bears large ziphodont teeth, a broad oreinirostral snout that is only slightly longer than 50% the skull length, and a deep adductor chamber in the temporal region and posterior mandibular ramus. The anterior region of its postcranial skeleton is preserved and shows broad scapula and a robust humerus features previously known in large predatorial notosuchians. The new crocodyliform adds to the predatorial component of terrestrial ecosystems at high paleolatitudes by the end of the Cretaceous Period.
Systematic paleontology
Crocodyliformes Hay, 1930
Mesoeucrocodylia Whetstone and Whybrow, 1980
Peirosauria Leardi et al., 2024
Peirosauridae Gasparini, 1982
Kostensuchus atrox gen. et sp. nov.
Etymology. Kosten, refers to the Patagonian wind in Aonikenk language; and suchus, latinized from the Greek Souchos in references to the Egyptian crocodile-headed god (Sebek). The species epithet atrox means harsh in Greek.
Holotype. MPM-PV 23554, articulated skull, jaws, cervical, axial skeleton remains including cervical, dorsal, and sacrals, rows of osteoderms along the vertebral sequence, cervical and dorsal ribs, scapular and pelvic girdles, complete right humerus and partial left humerus, and fragmentary remains of the hindlimbs.
Locality, horizon, and age. Lower section of the Chorrillo Formation, at Estancia La Anita, approximately 30 km SW from El Calafate city (Fig 1). The specimen comes from a concretionary level exposed at the locality “Puma cave” (locality 4, 5), approximately 60 meters from the base of the Chorrillo Formation.
Diagnosis. Kostensuchus gen. nov. is among the largest known peirosaurids (dorsal skull length = 49 cm) diagnosed by the following combination of characters (autapomorphies marked by *): skull proportionally shorter, wider and higher than in other peirosaurids (e.g., Hamadasuchus, Lomasuchus, Montealtosuchus); rostrum comprising slightly over 50% the total skull length; sinusoidal alveolar margin of maxilla (shared with Hamadasuchus); completely ossified internarial bar; lacrimal lateral surface faintly ornamented and slightly depressed between antorbital fenestra and orbit*; jugal reaching the ventral end of a circular antorbital fenestra; subtrapezoidal external supratemporal fenestra, occupying close to 70% of skull roof width; absence of anterior floor of supratemporal fossa; flat dorsal surface of parietal in occipital view; distinct step on dorsal surface of the posterolateral process of squamosal; broad palatine anterior margin, forming a bread transversal suture with maxilla; paired parasagittal ridges on the ventral surface of the basisphenoid; convex dorsal edge of surangular and craniomandibular articulation located above the level of dentary toothrow; ziphodont teeth; humerus with vertical orientation of insertion area of M. subscapularis above internal tuberosity; distal end of deltopectoral crest curves medially surpassing the lateromedial midpoint of humeral shaft; anterior surface of distal end of humerus separated from shaft by a distinct step forming a shelf.
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| Skull and jaw of Kostensuchus atrox gen. et sp. nov. Photographs in (A) right lateral, (B) dorsal, and (C) ventral views. Interpretative drawings in (D) right lateral, (E) dorsal, and (F) ventral views. Abbreviations: ang, angular; ap, anterior palpebral; de, dentary; ec, ectopterygoid; fr, frontal; j, jugal; la, lacrimal; mx, maxilla; pa, parietal; pal, palatine; pmx, premaxilla; pnf, perinarial fossa; po, postorbital; pp, posterior palpebral; pt, pterygoid; q, quadrate; qj, quadratojugal; na, nasal; rarp, retroarticular process; sang, surangular; sof, suborbital fossa; spl, splenial; sq, squamosal; stf, subtympanic foramen. Scale bar 5 cm. |
Fernando E. Novas, Diego Pol, Federico L. Agnolín, Ismar de Souza Carvalho, Makoto Manabe, Takanobu Tsuihiji, Sebastián Rozadilla, Gabriel L. Lio and Marcelo P. Isasi. 2025. A New large hypercarnivorous Crocodyliform from the Maastrichtian of Southern Patagonia, Argentina. PLoS One. 20(8): e0328561. DOI: doi.org/10.1371/journal.pone.0328561 [August 27, 2025]
