Friday, April 5, 2013

[Palaeontology • 2013] The affinities of ‘Steneosaurus barettoni(Crocodylomorpha, Thalattosuchia), from the Jurassic of Northern Italy, and implications for cranial evolution among geosaurine metriorhynchids


MPUP 6552 & Holotype of Neptunidraco ammoniticus

Abstract
In 1787, a fragmentary fossil skull of a crocodylian was discovered in the Altopiano dei Sette Comuni (Veneto, Northern Italy). In 1883, the specimen was referred to a new species of the teleosauroid Steneosaurus, S. barettoni. In this study, the specimen is redescribed and its taxonomic status reviewed. S. barettoni fails to conform to Article 12 of the International Code of Zoological Nomenclature and is considered as a nomen nudum. The specimen lacks synapomorphies of both Teleosauroidea and Steneosaurus, whereas it is referred to Metriorhynchidae based on the presence of an elongate median depression between the dorsal surface of nasals, and a large teardrop-shaped prefrontal that is expanded laterally. The combination of cranial and dental features present in this specimen supports its referral to Neptunidraco, an interpretation that adds new information on the morphology of the Italian metriorhynchid. Although total evidence analysis placed Neptunidraco as a basal divergence among Geosaurinae, it independently evolved some craniomandibular features previously considered exclusive of the macrophagous Geosaurini. This specimen is historically relevant because it may represent the first metriorhynchoid found worldwide.

Keywords: Crocodylomorpha, Italy, Jurassic, Neptunidraco , Thalattosuchia


Andrea Cau. 2013. The affinities of ‘Steneosaurus barettoni’ (Crocodylomorpha, Thalattosuchia), from the Jurassic of Northern Italy, and implications for cranial evolution among geosaurine metriorhynchids. Historical Biology.  DOI:10.1080/08912963.2013.784906

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