Abstract
Cenomanian beds from western France have yielded a new pythonomorph squamate (Reptilia) that is described here as Carentonosaurus mineaui gen. et sp. nov. This fossil is referred to non-mosasaurid mosasauroid lizards, i.e. to `aigialosaurs'. It has been found in sediments of marine origin and its anatomy con®rms that it was an aquatic lizard. It is characterized by a combination of characters that has not been reported, thus far, for squamates. Moreover, its vertebral column includes non-pachyostotic cervical vertebrae and highly pachyostotic dorsal vertebrae as in several other `aigialosaurs'. This new taxon is perhaps restricted to the upper Cenomanian. It lived in shallow and rather warm water of the inner shelf. It is worth mentioning that nearly all pachyostotic squamates are concentrated in the Cenomanian and/or lower Turonian deposits of the present European-North African-Middle East portion of the Tethys. A parallel is drawn between the high percentage of pachyostotic squamates and the fact that this period corresponds to both the largest transgression of the Phanerozoic and the warmest period in the whole of the Mesozoic and Caenozoic. Cenomanian beds (Ne Âraudeau et al. 1997 ) (Text-®g. 1B): (1) some vertebrae were collected from C4ms, the lower unit of the Upper Cenomanian 1; (2) the largest part of the material (vertebrae, one rib, and one fragmentary pectoral girdle) has been collected from the overlying Dm unit. The Dm unit belongs to the Upper Cenomanian Guerangeri Zone, dated by Thomelites cf. lattense and Pseudocalycoceras sp. (Ne Âraudeau et al. 1997) . The oldest vertebra, from C4ms, comes from a level located about 0´20 m above the boundary between C4ms and C3c, i.e. the boundary between the Middle and Upper Cenomanian. This boundary corresponds to a regional discontinuity and probably to the `Ce 4' sequence boundary of de Graciansky et al. (1998) . The youngest vertebra comes from a level located about 0´05±0´15 m above the base of Dm and approximately 1±1´20 m below the top of Dm, i.e. the boundary with the younger sandy unit Es (Ne Âraudeau et al. 1997) . Therefore, the lizard material as a whole was distributed through a stratigraphical thickness of about 0´50 m. D E P O S I T I O N A L E N V I R O N M E N T S The C4ms silty unit is interpreted as representing the beginning of a trangressive episode (not really as a `lowstand systems tract'; Ne Âraudeau et al. 1997) ; it corresponds to a very shallow environment. The invertebrate remains associated with the vertebrates are mainly fragmented rudists and stromatoporids derived from the previous reefal environments of the C3c unit. Some oysters and more rarely some spatangoid echinoids (Mecaster) comprise the other part of the invertebrate fauna. Apart from the lizard, vertebrates are represented only by ®sh (elasmobranchs: indeterminate cretoxyrhinids and neoselachians; actinopterygians: indeterminate pycnodontiforms) (D. Dutheil, pers. comm. 2000) . The energy level was relatively high at the time of deposition, in a palaeoenvironmental context close to the coast under wave action. The vertebrate-rich Dm unit corresponds to a highstand systems tract and a shallow environment open to outer shelf in¯uences. Lithologically, Dm is a silty limestone, generally yellow but locally grey, with local concentrations of organic matter (Ne Âraudeau 1991) and sometimes identi®able remains of land plants, such as Frenelopsis and Araucarioxylon (J. Dejax, pers. comm. 1999) . The invertebrate fauna associated with the vertebrate remains is very abundant and well preserved, combining organisms fossilized in situ, such as echinoids, and shells transported and brought in by currents, such as those of cephalopods. The allochthonous fauna of cephalopods comprises mainly Nautilus triangularis showing remains of the shell covered by epizoans. The in situ fauna of echinoids comprises mainly juvenile Mecaster grossouvrei, sometimes preserved with some of their spines (Area A in Ne Âraudeau 1991). These spatangoids with large ambulacra characterize silty and sandy substrates in shallow, temperate water (Ne Âraudeau 1995) . The Dm unit has yielded the same ®sh fauna as the C4ms unit, plus the elasmobranch Squalicorax (Anacoracidae). Finally, in the deposits from which the lizard has been collected (in both C4ms and Dm), organisms of various ecological af®nities are preserved together: land plants, echinoids of the shallow inner shelf, cephalopods of the deeper shelf. This association of different environmental components could be evidence of a depositional environment at the crossroads of marine and continental in¯uences, such as a lagoon (protected by a rudist reef?) or more likely a temporary reservoir of water (`baõ Ène' in French), isolated from the open sea during low tide by a sand bank but inundated during high tide. Diagnosis. As for the type and only known species.
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