JURASSIC MARINE VERTEBRATE REMAINS FROM THE UMBRIA-MARCHE DOMAIN (Central Italy): STRATIGRAPHICAL CONTEXT AND PALAEOECOLOGICAL SIGNIFICANCE

PAOLO CITTON; SIMONE FABBI; ANGELO CIPRIANI; MARCO ROMANO

Congreso; 3rd Palaeontological Virtual Congress Palaeontology in the virtual era; 2021

Isolated and fragmentary vertebrate fossil remains can provide useful constraints in reconstructing faunal composition and palaeoecological relationships in marine palaeoenvironments. The vertebrate record of the Jurassic succession of the Umbria-Marche Domain is represented by scattered remains from different lithostratigraphic units and ages, in distinct palaeostructural contexts within PCP-basin systems. The record is represented, to date, by: i) a trackway, named Accordiichnus natans, of an indeterminate marine ?reptile? (Pliensbachian); ii) teeth remains referred to Oxyrhina sp. (Toarcian - Erbaense Zone) and Sphenodus spp. (Pliensbachian, Bajocian?, Kimmeridgian); iii) a probable ichthyosaur rib (early Kimmeridgian) and a relatively complete, mostly articulated ophthalmosaurid ichthyosaur, Gengasaurus nicosiai (holotype, MSVG 39617) (late Kimmeridgian-earliest Tithonian); iv) multicuspid shark teeth referred to Hexanchiformes (late Kimmeridgian-earliest Tithonian), associated to Gengasaurus nicosiai and probably suggesting scavenging; v) polygonal teeth with domed or flat occlusal surface referred to Asteracanthus sp. (Toarcian) and Asteracanthus cf. magnus (Kimmeridgian); vi) button-like teeth (Kimmeridgian) referred to neoginglymodian actinopterygians. From a palaeoecological point of view, the fossil specimens likely represent indicate active nektonic carnivores, including different fast-swimming, fusiform sharks equipped with tearing and cutting dentitions, and durophagous sharks and bony fishes exhibiting, respectively, extreme crushing and tritorial (plus probably nipping) dentitions. The durophagous fauna fed on the rich invertebrate fauna (e.g. bivalves, gastropods, echinoids, crustaceans, brachiopods) dwelling the sea-floor of PCP-basin systems, whose enucleation and development related to the Early Jurassic Western Tethys Rifting most likely played a role in increasing niche availability in a purely pelagic domain.