The Mesozoic Formations outcropping in Lombardy (northern Italy), represented by world-wide renowned fossiliferous localities as Besano (Varese Province), Cene and Endenna (Bergamo Province), have yielded an extraordinarily rich reptile fauna dating almost exclusively to the Middle and Late Triassic. Cretaceous evidences are limited to a plesiosaur humerus from the Campanian-Santonian of Zavattarello (Pavia Province), while Jurassic reptiles have been reported so far only in the Sinemurian locality of Saltrio, where dinosaur remains have been recently discovered.
The new findings here described come from the outskirts of Cesana Brianza (Lecco Province), where an Early Jurassic (Toarcian) layer of the Sogno Formation outcrops. The material consists of the remnants of two partial specimens (MSNM V4012 and V4013a, b), one of which preserved as part and counterpart. Most of the available skeletal elements are in anatomical connection, fossilised on slabs but well preserved in three dimensions and not showing any sign of erosion or damage due to post-mortem transport. Some of the elements, or part of them, are represented by imprints in a matrix that, being fine-grained, allow to identify in detail the original bone shape and, sometimes, surface morphology. Organic remains, possibly integumentary structures, are preserved in form of a black halo surrounding the caudal vertebrae of MSNM V4013. Both specimens are small in size (vertebral centra average length around 10 mm), and lack of skull, anterior trunk vertebrae and front limbs. They are characterised by amphicoelous presacral vertebrae (with open neurocentral sutures), long and slender hind limbs, and a relatively well developed armour of osteoderms.
The available features match well with Thalattosuchian "crocodiles", and their allocation to the teleosaurid genus Steneosaurus or the metriorhynchid Pelagosaurus is still being evaluated. Jurassic reptiles are rather rare in Italy, but the discovery of thalattosuchian remains in at least 6 Jurassic localities comprised within a relatively wide area of northern Italy (extended across Lombardy, Trentino, Veneto and possibly Friuli-Venezia Giulia) allows to consider the presence of these "marine crocodiles" as far from being sporadical. Although poor preparation and absence of well preserved cranial elements hinder a proper taxonomic allocation of the Italian findings, both Teleosauridae (genus Steneosaurus) and Metriorhinchidae (genus Metriorhyncus) families have been quoted.
The Cesana thalattosuchians here described are among the oldest "crocodiles" ever found in Italy. They are rather peculiar because their very small size contrasts with that of the Italian specimens referred to "putative" Steneosaurus. According to Brochu, the hatchlings of the Crocodylia show fully closed neurocentral suture in caudal vertebrae only, and closure follows a caudal to cranial sequence during ontogeny. The status shown by the Cesana thalattosuchians matches with such pattern, providing a size-independent criterion to asses the non mature condition of the specimens, and suggests that the usefulness of this criterion can be extended to mesoeucrocodylians too.


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