Pietraroiasuchus, Buscalioni & Piras & Vullo & Signore & Barbera, 2011

Buscalioni, Angela D., Piras, Paolo, Vullo, Romain, Signore, Marco & Barbera, Carmela, 2011, Early eusuchia crocodylomorpha from the vertebrate-rich Plattenkalk of Pietraroia (Lower Albian, southern Apennines, Italy), Zoological Journal of the Linnean Society 163 (5), pp. 644-645 : 644-645

PIETRAROIASUCHUS

Bausch & Bravi (1999) reconstructed a shallow lagoonal environment for the vertebrate-bearing beds of Pietraroia, close to land and frequently isolated from the open sea, but subject to tidal influence and occasional storms. The level of salinity of the water would therefore have varied, as is reflected in the rock layers that show varying marine and terrestrial influences. The low-lying landmass with which the deposit was associated was one of a chain of islands running for perhaps 100–200 km, rather like the Antilles or Bermuda island chains today. A new depositional environmental model was recently put forward by Carannante et al. (2006), who suggested that the vertebrate-rich Plattenkalk sequences were the deposits resulting from an abandoned submarine channel associated with a transgressive event that provoked the development of suboxic conditions on the seabed. We may assume that Pietraroiasuchus was a margino-littoral form, with an ecology linked to brackish or marine aquatic environments. However, its exact lifestyle and behaviour are not really known, given that many of the singular morphological adaptations of this enigmatic genus have no modern analogues. Was it mainly an aquatic or semi-aquatic (amphibious) form? If aquatic, could it have been a marine form?

It is worth noting that the vertebrae and some other skeletal elements (e.g. ribs, coracoid) of Pietraroiasuchus are robust and massively built, as observed in several Albian–Cenomanian pachyostotic lepidosaurs ( Reynoso, 2000; Rage & Néraudeau, 2004; Houssaye et al., 2008). These reptiles (e.g. Ankylosphenodon , Simoliophis , Carentonosaurus ) are all considered to be coastal marine forms and most of them lived in the Mediterranean Tethys. For example, Reynoso (2000) has suggested that the rhynchocepha- lian Ankylosphenodon from the Albian of Tepexi behaved in a similar manner to the extant marine iguanid Amblyrhynchus . Pietrarioiasuchus seems to represent the first pachyostotic crocodyliform other than the mid-Cretaceous lepidosaur group mentioned above.

de Ricqlès (1989) argued that pachyostosis in tetrapods would be characteristic of animals that are incompletely adapted to marine life. Such animals partly belong to Carroll’s (1985) Category 5, which includes forms that have unmodified (without paddles) and unreduced limbs. Pietraroiasuchus , which may have been able to swim by laterally undulating its tail, clearly belongs to this group. Note that P. ormezzanoi has a proportionally long tail, with a first biconvex centrum, both of which features are optimal for swimming.

Skull and tooth morphology provide further information about the feeding behaviour of Pietraroiasuchus . Its dentition shows little real specialization. The slender, thin, homodont conical teeth are characteristic of piscivorous forms. Such teeth are present in various Jurassic–Cretaceous marine crocodilyforms, as in some teleosaurids ( Vignaud, 1997), pholidosaurids ( Hua et al., 2007), and dyrosaurids ( Wu, Russell & Cumbaa, 2001). However, all these forms are longirostrine crocodyliforms, unlike Pietraroiasuchus , which is clearly a brevirostrine taxon. The posterior teeth of Pietraroiasuchus seem to have been shorter and more robust although not molariform. The skull, characterized by a broad and dorsoventrally flattened snout, is small and short relative to the body length. The mandible is anteriorly spatulated and flat, and its anterior half is narrower than the upper jaw, as occurs convergently in Anatosuchus minor ( Sereno et al., 2003) . The anterior teeth of the Pietraroiasuchus mandible were probably not trophically functional as they were hypotrophied. Thus, the feeding mechanism would be focused at the posterior part of the mouth, thereby explaining the strong musculature that Pietraroiasuchus would have developed in accordance with the surangular anterodorsal process and the position of the mandible placed above the level of the tooth row. In these features Pietraroiasuchus resembles Iharkutosuchus makadii ( Ösi & Weishampel, 2009) , but, surprisingly, the posterior teeth are not molariform as in Iharkutosuchus and Hylaeochampsa , raising the possibility of a new combination of traits for a crushing jaw and musculature combined with a delicate dentition. The presence of the singular maxillary lip should not be discounted as a possible trophic device in Pietraroiasuchus . All these anatomical and morphological features indicate that Pietraroiasuchus , a coastal crocodyliform partially adapted to marine life, was probably not strictly piscivorous. In a shallow, near-shore environment, it probably preyed upon relatively small fish (e.g. semionotids, pycnodontids) and invertebrates such as crustaceans.

This life reconstruction is in accordance with that proposed for Pachycheilosuchus ( Rogers, 2003) . The biotope of the Texan genus from the Glen Rose Formation was interpreted by Rogers (2003) as being a shallow, near-shore, protected, brackish-water environment. Rogers illustrated a reconstruction, on the basis of the evidence of the depositional environment and the associated fauna, of the life cycle of Pachycheilosuchus , in which it is represented as an aquatic, active, fish-eating form.