The Hybodontiformes sharks ( Chondrichtyes: Euselachii)from the Upper Jurassic of Torres Vedras, Portugal

Abstract

The hybodontiforms were a group of sharks that lived in oceans and freshwater environments, appearing in the Late Devonian and persisting until the Late Cretaceous, when they became extinct. Up until now, very few occurrences of hybodonts were documented in Portugal. Only isolated teeth and scales, as well as cephalic and dorsal fin spines are known in the country. In the 1960s, an isolated tooth of Asteracanthus sp. was collected at the Fonte Quente limestone quarry. In the Guimarota coalmine, between 1995 and 2004, fossil remains were attributed to Hybodus lusitanicus, Asteracanthus biformatus, Hybodus sp., and Hybodontoidea indet. In 2003, isolated teeth and spines collected from Peralta and Porto das Barcas, Lourinhã, were regarded as Hybodus cf. reticulatus. Recently, in 2018, additional material of (probably) H. lusitanicus was collected from Porto das Barcas. Both fossil material abundance and diversity, however, are relatively scarce, since the clade Hybodontiformes only represents less than 1% of the entirety of fossil chondrichthyans described in Portugal. In this study, isolated tooth samples from the marine deposits of the top of Praia Azul Member, Sobral Formation, Lusitanian Basin, dating between late Kimmeridgian and early Tithonian, were analyzed and classified for the first time in Torres Vedras municipality. The dental characters of the thirty (30) specimens matches those of Hybodus reticulatus, whose evidence is most notorious on the main cusp, cutting-edges, and, especially, the root. As a result, the samples were attributed to this species, its presence being confirmed here in the Portuguese record. This work aims to continue the research regarding the diversity and occurrences of fossil selachians, and will hopefully add more knowledge to the Hybodontiformes from the Upper Jurassic of Portugal.