The fate of supposed plesiosaur vomit from Jurassic delta deposits offshore Norway

Regurgitalites (fossilized vomit) have been recognized as such for a century, but only recently they became better understood and systematically described. Centimetre-sized clumps containing tightly packed skeletal material of invertebrates (e.g. bivalves, serpulids and crinoids) and plant fragments are reported from well-core material offshore Norway for the first time. They occur in numerous wells with continuous cores through Middle to Upper Jurassic (Bathonian to Oxfordian) siliciclastic successions. The clumps mainly occur in delta-front deposits with records of salinity fluctuation due to incoming freshwater. This contrasts with their composition, consisting of stenohaline forms. The tight fabric, diverse composition, co-occurrence of fractured and complete organisms, and etched margins are consistent with an interpretation as regurgitalites. This biologically introduced allochthonous material differs from physically deposited skeletal concentrations (e.g. in storm layers) by their localized distribution (few centimetres). Delta-front environments are dynamic systems with a high sedimentation rate and frequent bioturbation. Consequently, the gastric pellets are subject of reworking and alteration, resulting in their disintegration or incorporation into burrows. An evaluation of potential producers of the regurgitalites – based on functional morphology and stomach content – infers that Cryptoclididae are most likely (although Hybodontiformes cannot be ruled out), which agrees with their abundance and stratigraphic distribution in the basin. Accordingly, these long-necked plesiosaurs were bottom-feeding on offshore epi-and infauna and regularly egested undigestible food remains nearshore, where it became preserved. The regurgitalites are ichnotaxonomically described as Vomitus igen. nov., including V. concha isp. nov., V. serpula isp. nov. and V. echinoderma isp. nov.