Late Barremian-Early Aptian palaeoenvironmental change: the Cassis-La Bedoule section (SE France)

The well-dated section of Cassis-La Bédoule in the South Provencal Basin (southern France) allows for a detailed reconstruction of palaeoenvironmental change during the latest Barremian and Early Aptian. For this study, phosphorus (P) and clay-mineral contents, stable-isotope ratios on carbonate (δ13Ccarb) and organic matter (δ13Corg), and redox-sensitive trace elements (RSTE: V, U, As, Co, and Mo) have been measured in this historical stratotype. The base of the section consists of rudist limestone, which is attributed to the Urgonian platform. The presence of low P and RSTE content, and content of up to 30% kaolinite indicate deposition under oligotrophic and oxic conditions, and the presence of warm, humid climatic conditions on the adjacent continent. The top of the Urgonian succession is marked by a hardground with encrusted brachiopods and bivalves, which is interpreted as a drowning surface. The section continues with a succession of limestone and marl containing the first occurrence of planktonic foraminifera. This interval includes several laminated, organic-rich layers recording RSTE enrichments and high Corg:Ptot ratios. The deposition of these organic-rich layers was associated with oxygen-depleted conditions and a large positive excursion in δ13Corg. During this interval, a negative peak in the δ13Ccarb record is observed, which dates as latest Barremian. This excursion is coeval with negative excursions elsewhere in Tethyan platform and basin settings and is explained by the increased input of light dissolved inorganic carbon by rivers and/or volcanic activity. In this interval, an increase in P content, owing to reworking of nearshore sediments during the transgression, is coupled with a decrease in kaolinite content, which tends to be deposited in more proximal areas. The overlying hemipelagic sediments of the Early Aptian Deshayesites oglanlensis and D. weissi zones indicate rather stable palaeoenvironmental conditions with low P content and stable δ13C records. A change towards marl-dominated beds occurs close to the end of the D. weissi zone. These beds display a long decrease in their δ13Ccarb and δ13Corg records, which lasted until the end of the Deshayesites deshayesi subzone (corresponding to C3 in Menegatti et al., 1998). This is followed by a positive shift during the Roloboceras hambrovi and Deshayesites grandis subzones, which corresponds in time to oceanic anoxic event (OAE) 1a interval. This positive shift is coeval with two increases in the P content. The marly interval equivalent to OAE 1a lacks organic-rich deposits and RSTE enrichments indicating that oxic conditions prevailed in this particular part of the Tethys ocean. The clay mineralogy is dominated by smectite, which is interpreted to reflect trapping of kaolinite on the surrounding platforms rather than indicating a drier climate

Anatomy and relationships of Pachyrhachis problematicus, a primitive snake with hindlimbs

The anatomy of Pachyrhachis problematicus, an elongate, limb-reduced squamate from the Upper Cretaceous of Israel, is described and evaluated in detail. Previously considered a snake-like 'lizard' of uncertain affinities, it is here shown to be the most primitive snake, and the sister-group to all other snakes. Pachyrhachis exhibits numerous derived characters uniting it with modern snakes (scolecophidians and alethinophidians): e.g. mobile premaxilla-maxilla articulation, braincase enclosed by frontals and parietals, sagittal parietal crest, absence of tympanic recess, single postdentary bone, over 140 presacral vertebrae, and complete loss of shoulder girdle and forelimb. However, it is more primitive than all modern snakes in retaining some strikingly primitive (lizard-like) features: presence of a jugal, squamosal, normal sacral attachment, and well-developed hindlimb composed of femur, tibia, fibula, and tarsals. Pachyrhachis provides additional support for the hypothesis that snakes are most closely related to Cretaceous marine lizards (mosasauroids). Almost all of the derived characters proposed to unite snakes and mosasauroids are highly developed in Pachyrhachis: the mobile mandibular symphysis, intramandibular joint, long and recurved pterygoid teeth, quadrate suspended by the supratemporal, loosely united pelvic elements (ilium, ischium, and pubis), and separate astragalus and calcaneum