A new species of Halisaurus from the Late Cretaceous phosphates of Morocco, and the phylogenetical relationships of the Halisaurinae (Squamata: Mosasauridae)

A new species of the basal mosasaurid Halisaurus from the Late Cretaceous (Late Maastrichtian) of the Oulad Abdoun Phosphate Basin of Morocco is described on the basis of both cranial and postcranial remains. H. arambourgi sp. nov. is characterized by unique features of the nares, frontal, parietal, girdle and limb bones. A phylogenetical analysis supports the monophyletic status of Halisaurus ; H. platyspondylus (Maastrichtian, New Jersey), H. ortliebi (Maastrichtian, Belgium) and H. arambourgi form an unresolved polytomy. This study does not support the attribution of ' Halisaurus ' sternbergii (Santonian, Kansas) to Halisaurus nor to any known genus. A new genus, Eonatator , is proposed for the reception of this species, Eonatator sternbergii comb. nov. The new taxon Halisaurinae ( Halisaurus  +  Eonatator ) is the sister-group of more advanced mosasaurids (Natantia). Halisaurines are defined by the shape of the lateral premaxilla–maxilla suture; an oblique contact plane between the parietal and the supratemporal; a preaxial ridge present on the distal two-thirds of the radius length; and tibia and fibula long and slender with slightly expanded extremities.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 143 , 447–472.     

Characterization and astronomically calibrated age of the first occurrence of Turborotalia frontosa in the Gorrondatxe section, a prospective Lutetian GSSP: implications for the Eocene time scale

The Gorrondatxe section, a prospective Lutetian Global Stratotype Section and Point (GSSP), has recently been used as the master reference section to reassess the correlation between Eocene magnetostratigraphic and calcareous planktonic biostratigraphic scales. However, the exact calibration of some events remained ill defined, as they were thought to be missing in Gorrondatxe due to a fault. The most important missing events were the first occurrence of the planktonic foraminifera Turborotalia frontosa and the C22n/C21r chron boundary. Either might be a reliable correlation criterion for the Ypresian/Lutetian boundary, as both approach the age of the original Lutetian Stratotype. New studies allowed the identification of the former event 9 m above the Gorrondatxe fault, within magnetic polarity Chron C21r and calcareous nannofossil Zone CP12a. Distinctive test features that characterize the most primitive morphotype of T. frontosa are described. Despite the high turbidite content, recurrent pelagic limestone–marl couplets and bundles occur, whose formation was driven by precession and eccentricity astronomical cycles. The first occurrence of T. frontosa was found 27 couplets and 5.5 bundles (60 m) below the first occurrence of the calcareous nannofossil Blackites inflatus , which is dated at 48 Ma. Hence, the age of the first occurrence of T. frontosa is estimated at 48.55 Ma, confirming that it is the most suitable planktonic foraminiferal correlation criterion for the Ypresian/Lutetian boundary. These results show that the stratigraphic interval missing due to the Gorrondatxe fault cannot be greater than a few metres and reinforce the value of this section as a prospective Lutetian GSSP.     

Reassessment of the Early–Middle Eocene biomagnetochronology based on evidence from the Gorrondatxe section (Basque Country, western Pyrenees)

Thirteen Lower–Middle Eocene (Ypresian–Lutetian) successions, including the Gorrondatxe section in the western Pyrenees, show biomagnetostratigraphic correlation schemes that do not agree with the current standard framework. The main discrepancy concerns the position of the boundary between planktonic foraminiferal Zones P9 (=E7, approximately) and P10 (=E8, approximately), which was thought to occur within calcareous nannofossil Subzone CP12a and at the boundary between magnetic polarity Chrons C22n and C21r. However, in the differing correlation scheme the boundary between Zones P9 (=E7) and P10 (=E8) occurs close to the base of Subzone CP13a and to the boundary between Chrons C21n and C20r. An attempt at a new Ypresian–Lutetian boundary biomagnetochronology is made based on data from the Gorrondatxe section, which shows that the boundary between Zones P9 (=E7) and P10 (=E8) is 3.1 Myr younger than hitherto considered. Therefore, the duration of the Early Eocene, most commonly defined according to this planktonic foraminiferal zonal boundary, has generally been underestimated over the last four decades.     

Specialization of bone structure in Pachyvaranus crassispondylus Arambourg, 1952, an aquatic squamate from the Late Cretaceous of the southern Tethyan margin

The histological organization of the vertebrae of the Maastrichtian squamate Pachyvaranus crassispondylus Arambourg, 1952 , was compared to that of various extant squamates, in order to further document the causes and functional consequences of the so-called 'pachyostosis', frequently observed in Late Cretaceous squamates. The vertebrae of Pachyvaranus are composed of the same basic bone tissue types as those of extant lizards and snakes. In particular, periosteal cortices are made of a pseudolamellar (or 'parallel-fibred') tissue, with radial vascular canals, Sharpey's fibres and conspicuous cyclic growth marks that are strictly identical to that found in extant varanids. Conversely, the vertebrae of Pachyvaranus are extremely compact, whereas those of extant squamates are very cancellous and lightly built. This difference is due to the absence in Pachyvaranus of a broad internal resorption field that, in extant lizards and snakes, transforms compact cortices into loose spongy formations. This absence of inner bone resorption typically corresponds to an osteosclerotic process. In Pachyvaranus , cortical hyperplasy, or pachyostosis stricto sensu , was restricted to the walls of the neural spine. Extreme vertebral porosity is likely to be a primitive condition in squamates, because all lizards and snakes examined in this study display this feature. Therefore, the high vertebral compactness observed in Pachyvaranus would be a derived condition arising from the loss (or de-differentiation) of a morphogenetic process: the broad internal resorption of the vertebrae. Possible palaeoecological bearings of these results are discussed.     

Galvechelone lopezmartinezae gen. et sp. nov., a new cryptodiran turtle in the Lower Cretaceous of Europe

Abstract: The Spanish town of Galve (Teruel) is notable because of the abundance of Upper Jurassic and, especially, Lower Cretaceous vertebrates recorded there. Although most groups have been studied in detail, information on turtles is very limited even though the material is relatively abundant. So far, no turtle taxa have been identified at the generic level. The only Lower Cretaceous articulated specimen from Galve is analysed here. It is identified as a representative of Cryptodira, Galvechelone lopezmartinezae gen. et sp. nov. Galvechelone lopezmartinezae is determined as a taxon belonging to the node that groups the turtles traditionally assigned to ‘Macrobaenidae’ and ‘Sinemydidae’, and other taxa such as the members of Panchelonioidea. This node, very abundant in the Lower Cretaceous of Asia, and with a broad subsequent distribution, has recently been recognized in the Lower Cretaceous of Europe. The diversity of basal members of Eucryptodira in the European Late Jurassic (represented by Thalassemydidae, Plesiochelyidae and Eurysternidae) was high. Owing to a relative scarcity of well‐preserved early Cretaceous turtles from Europe, the knowledge of this group of reptiles is limited. The study of the new turtle from Galve, together with the recently described Hoyasemys jimenezi, and the recently completed review of the enigmatic Chitracephalus dumonii demonstrate that members of the cryptodiran node grouping ‘Macrobaenidae’, ‘Sinemydidae’ and Panchelonioidea were also very diverse in this period.