A Late Cretaceous madtsoiid snake from Romania associated with a megaloolithid egg nest – Paleoecological inferences

• Taphonomy of the Nidophis insularis type series shows it represents one individual.
• Average size of Nidophis insularis was about 1 m in length.
• Age estimation of the type individual was possible using apophyseal growth rings.
• Although found in a dinosaur nest, Nidophis was clearly not a dinosaur nest raider.
• Bite mark on one vertebra suggests predation or scavenging on Nidophis.

Here we report on the taphonomy and paleoecological implications of the first record of a small madtsoiid snake (Nidophis insularis) closely associated with a megaloolithid dinosaur egg nest. Taphonomic and sedimentologic evidence suggest that the snake was buried autochthonously within or nearby the egg nest, with at least partially articulated skeleton. Count of growth rings on the vertebral zygapophyses indicates that the holotype of Nidophis belonged to an adult individual approaching the limit of its maximum body size of about 1 m length. The presence of layers of arrested growth on the zygapophyses, together with other independent data (e.g., paleomagnetic data, sedimentology, paleosol development stage, stable isotope geochemistry) indicates that Nidophis lived under a semi-arid, seasonally variable subtropical climate, having alternative periods of active feeding. The trunk vertebrae with relatively low neural spines and without prezygapophyseal accessory processes indicate a relatively heavy-bodied, slowly-moving animal, one that probably had a semifossorial habit and was an active forager, but definitively not a dinosaur nest raider as suggested for certain large madtsoiid snakes (the Indian Sanajeh). Potential prey items, available around the dinosaur nesting area, probably ranged from small squamate eggs to various small vertebrates. Finally, one anterior trunk vertebra of the holotype displays distinct bite marks left by a small-sized and pointed-toothed predator, most probably a crocodyliform or a theropod, thus documenting that madtsoiids were also preyed upon.