Abstract
Metriorhynchidae is an extinct group of Jurassic–Cretaceous crocodylomorphs that developed a fully pelagic lifestyle. Its Jurassic record is outstanding (it includes around 40 nominal species), while the records that can be restricted to the Cretaceous are particularly sparse. Here we describe a partial skull of a new species of Cricosaurus, Cricosaurus puelchorum sp. nov., from the lower Berriasian of the Vaca Muerta Formation (Neuquén Basin, Argentina). The description of the specimen reveals a series of autapomorphies and a unique combination of characters that justify the creation of a new species. Phylogenetic analysis places Cricosaurus puelchorum sp. nov. closer to three upper Kimmeridgian–lower Tithonian species of southern Germany. The new taxon was recovered in connection with an accurate ammonoid-based biostratigraphic control and allows confirming the survival of Cricosaurus across the J/K boundary at the southeastern Pacific.
Highlights
IntroductionArchosauria group adapted to a pelagic lifestyle as it is documented by several morphological and physiological modifications such as laterally directed orbits, reduced and paddle-like forelimbs, loss of osteoderms, regionalized caudal vertebral column with a hypocercal tail, and hypertrophied nasal glands for salt excretion, among others (e.g. Fraas, 1902; Andrews, 1913; Fernández and Gasparini, 2008; Young et al, 2010; Herrera et al., 2013a; Sachs et al, 2019)
Groebericeras bifrons is interpreted as a lower Berriasian marker in the Neuquén Basin and it is usually recorded at the very base of the Argentiniceras noduliferum Zone (Leanza, 1945; Aguirre-Urreta and Álvarez, 1999; Vennari et al, 2012; Parent et al, 2015; Vennari and Aguirre-Urreta, 2017)
Time-calibrated phylogenetic analysis shows a decrease in Cricosaurus species richness from the late
Summary
Archosauria group adapted to a pelagic lifestyle as it is documented by several morphological and physiological modifications such as laterally directed orbits, reduced and paddle-like forelimbs, loss of osteoderms, regionalized caudal vertebral column with a hypocercal tail, and hypertrophied nasal glands for salt excretion, among others (e.g. Fraas, 1902; Andrews, 1913; Fernández and Gasparini, 2008; Young et al, 2010; Herrera et al., 2013a; Sachs et al, 2019). Except for the holotype (and the only specimen know) of Purranisaurus potens for which an upper Tithonian–lower Berriasian age was determined based on an associated ammonite shell (Herrera et al, 2015), the age of the other metriorhynchids specimens from Mendoza Province is not accurately constrained. We describe a new species which represents the first definitively Cretaceous metriorhynchid from the Vaca Muerta Formation (Neuquén Basin, Argentina), and showing the survival of Cricosaurus across the J/K boundary in the High Andes Groebericeras bifrons is interpreted as a lower Berriasian marker in the Neuquén Basin and it is usually recorded at the very base of the Argentiniceras noduliferum Zone (Leanza, 1945; Aguirre-Urreta and Álvarez, 1999; Vennari et al, 2012; Parent et al, 2015; Vennari and Aguirre-Urreta, 2017). Sammlungen Bayerns- Bayerische Staatssammlung für Paläontologie und Geologie, München, Germany
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