Skull morphology modification and dietary differences in the Triassic small protorosaurs Macrocnemus and Langobardisaurus.

Skull morphology modification and dietary differences in the Triassic small protorosaurs Macrocnemus and Langobardisaurus Renesto S.1 1 Department of Structural and Functional Biology, Università degli Studi dell’Insubria, via Dunant 3 Varese Italy, silvio.renesto@uninsubria.it Abstract The Protorosauria Huxley 1881 (Prolacertiformes Camp 1945) constitutes a clade of mainly Triassic reptiles among which the genera Macrocnemus, Tanystropheus and Langobardisaurus from the Middle and Late Triassic of Northern Italy, Switzerlandand and recently China, are the best known ones. All genera share the same skeletal architecture, characterized by a long neck formed via elongation of individual vertebrae rather than an increase in their number (with an extreme in Tanystropheus); and a great disparity in length between fore- and hind-limbs. Tanystropheus was aquatic or semiaquatic with different species showing great size variability from the medium-sized T. meridensis, (approx 1,5m long) to the very large T. longobardicus, (up to 5 m long), while both Macrocnemus and Langobardisaurus were smaller, swift terrestrial reptiles, able of bipedal gait during fast run. One of the major differences among the similar sized terrestrial taxa (Macrocnemus and Langobardisaurus) can be found in the dentition and skull architecture: Macrocnemus had simple homodont dentition with small sharp teeth ad a lightly built skull, with sleder jaws, a pattern that fits easily with the model of a carnivore which fed on invertebrates or small vertebrates which were swallowed whole or after very little processing. Langobardisaurus had instead a robust, short and high skull, with a deep lower jaw, peg-like front teeth (absent in the lower jaw) followed by few bulky three-cusped teeth and a large, flattened molariform last tooth and its feeding habits are more difficult to be interpreted. An analysis of the functional and mechanical implications of the dentition, of the skull and of the lower jaw, along with a reconstruction of the jaw musculature by comparison with extant durophagous and herbivorous diapsids and anapsids, suggests that Langobardisaurus was able of complex food processing and may have been an omnivore which fed on hard and/or though food, possibly comprising vegetals.