[Palaeontology, Vol. 56, Part 3, 2013, pp. 647–661] NEW HIGHLIGHTS ABOUT THE ENIGMATIC MARINE SNAKE PALAEOPHIS MAGHREBIANUS (PALAEOPHIIDAE; PALAEOPHIINAE) FROM THE YPRESIAN (LOWER EOCENE) PHOSPHATES OF MOROCCO by ALEXANDRA HOUSSAYE1,2*, JEAN-CLAUDE RAGE1, NATHALIE BARDET1, PEGGY VINCENT3, MBAREK AMAGHZAZ4 and SAID MESLOUH5 1De´partement Histoire de la Terre, UMR 7207 du CNRS, Muse´um National d’Histoire Naturelle, 57 rue Cuvier CP 38, 75005 Paris, France; e-mails: [email protected], [email protected], [email protected] 2Steinmann Institut fu¨r Geologie, Pala¨ontologie und Mineralogie, Universita¨t Bonn, Nussallee 8, 53115 Bonn, Germany; e-mail: [email protected] 3Staatliches Museum fu¨r Naturkunde Rosenstein 1, D-70191 Stuttgart, Germany; e-mail: [email protected] 4Office Che´rifien des Phosphates, Centre Minier de Khouribga, Khouribga, Morocco; e-mail: [email protected] 5Ministe`re de l’Energie, des Mines, de l’Eau et de l’Environnement, Rabat, Morocco; e-mail: [email protected] *Corresponding author. Typescript received 23 March 2012; accepted in revised form 4 September 2012 Abstract: Palaeophis maghrebianus belongs to the Palaeo- analysis of some vertebrae illustrating diverse positions along phiinae (Palaeophiidae). This snake subfamily is relatively the vertebral column reveals the presence of osteosclerosis, poorly known, and it is mainly represented by disarticulated especially in the anterior and mid-precloacal regions. The vertebrae and ribs and by a few vertebral segments. Its intracol- occurrence of this osseous specialization implies a role in umnar variability remains also poorly understood. The discovery buoyancy and body trim control in this taxon, which is consid- of new isolated vertebrae and vertebral segments of Palaeophis ered a shallow marine dweller based on its anatomical features maghrebianus in the Ypresian (Lower Eocene) Phosphates of and geological data. Palaeophis maghrebianus also displays a Morocco enables us to provide a more detailed diagnosis of dense vascular network suggesting a growth speed, and thus a this species and to describe its intracolumnar variability. metabolic rate, much higher than in the biggest extant snakes. Moreover, the new material reveals that this species could reach gigantic size being, with Palaeophis colossaeus, one of the Key words: snakes, Palaeophiidae, palaeobiology, palaeoe- two longer palaeophiids. The microanatomical and histological cology, gigantism, histology. Palaeophiinae Lydekker, 1888 (Squamata, Ophidia) 2003). Moreover, the morphological variations along the lived from the Maastrichtian to the Late Eocene (Rage vertebral column remain rather unknown, so that infer- et al. 2003). This subfamily, which includes the two gen- ring the original position of vertebrae along the vertebral era Palaeophis Owen, 1841 (Maastrichtian–Eocene) and column is still extremely difficult. Palaeophiinae includes Pterosphenus Lucas, 1899 (Eocene) is, with the subfamily a wide range of species sizes. The biggest species so far is Archaeophiinae Janensch, 1906, part of the family Palaeo- considered to be Palaeophis colossaeus Rage, 1983a, esti- phiidae Lydekker, 1888. Palaeophiidae is one of the mated to be about 9 m long (Rage 1983b), whereas the only five extinct families (with Anomalophiidae Auffen- smallest species P. casei Holman, 1982 was apparently berg, 1959; Nigerophiidae Rage, 1975; Pachyophiidae about 1–1.3 m long (Parmley & Reed 2003). This subfam- Nopcsa, 1923; and Russellophiidae Rage, 1978) among ily includes various species illustrating three ecological Ophidia that adapted to various freshwater and marine grades. The ‘primitive’ Palaeophis grade (sensu Rage et al. environments. 2003) comprises species with vertebrae only slightly modi- Palaeophiine snakes are in fact relatively poorly known; fied for an aquatic life, whereas the ‘advanced’ Palaeophis the material available consists only of disarticulated verte- grade (sensu Rage et al. 2003) includes species with verte- brae and ribs and of a few vertebral segments (Rage et al. brae clearly modified for an aquatic life (see Rage et al. ª The Palaeontological Association doi: 10.1111/pala.12008 647 648 PALAEONTOLOGY, VOLUME 56 2003 for more details). The third grade is comprised only GEOLOGICAL SETTING of Pterosphenus, whose vertebrae are highly modified for an aquatic life. The Phosphates of Morocco, exploited as an economical The species P. maghrebianus Arambourg, 1952 is one of resource since the 1920s (Office Cherifien des Phosphates the better documented species, but it has not been revised 1989), are part of the ‘Mediterranean Tethyan phospho- since its original description by Arambourg (1952). It is genic Province’, a large belt of sedimentary deposits only known from the Ypresian Phosphates of Morocco. It located around palaeolatitude 20°S that currently crops is the only squamate discovered in the Ypresian of out widely from the Middle East up to the Pernambuco Moroccan Phosphates so far (Bardet et al. 2010). This Province of Brazil, via North and West Africa (Lucas and large snake is considered aquatic based on its vertebral Pre´voˆt-Lucas 1996). In Morocco, these phosphates crop morphology (Bardet et al. 2010). However, it belongs to out into two main exploited, large areas known as the the ‘primitive’ Palaeophis grade (cf. Rage et al. 2003). Oulad Abdoun and the Ganntour basins (Fig. 1A). Strati- The discovery of new isolated vertebrae and three artic- graphically, the phosphatic strata of Morocco range in age ulated vertebral segments, which correspond to the lon- from the Late Cretaceous (Maastrichtian) to the Middle gest vertebral segments known for a palaeophiine, enabled Eocene (basal Lutetian), spanning the longest time interval us to obtain new anatomical data about this species. of all Tethyan phosphates (Lucas & Pre´voˆt-Lucas 1996). Moreover, the microanatomical and histological features The Lower Eocene phosphatic series in the Oulad of some vertebrae were investigated to obtain new infor- Abdoun basin is the most developed compared to the Ma- mation about the biology of this taxon and to discuss its astrichtian (Bed IIII) and Danian–Thanetian (Bed II) beds. palaeoecology. The Ypresian levels include several levels and horizons, A B C FIG. 1. Geographical and stratigraphical occurrences of Palaeophis maghrebianus Arambourg, 1952 in Morocco. A, location of the main phosphatic basins. B, details of the Oulad Abdoun basin. C, synthetic stratigraphical column of the phosphatic series in the Daoui zone, NE part of the Oulad Abdoun basin, where most specimens of P. maghrebianus have been found in the Intercalary beds II ⁄ I to bed 0 (Ypresian). (A–B) Modified from Bardet et al. (2010) and (C) from Sole et al. (2009). HOUSSAYE ET AL.:NEWHIGHLIGHTSABOUTPALAEOPHIS MAGHREBIANUS 649 which are, from bottom to top, Bed I, 0¢ and 0, and troughs MATERIALS AND METHODS B and A (Fig. 1C). All of these more or less soft phosphatic levels are separated by hard calcareous phosphatic beds Materials. The material consists of 163 isolated vertebrae, called Intercalary beds. The Lower Eocene phosphatic series including the ones originally described by Arambourg in the Ganntour basin is less expansive than the Maastrich- (MNHN APH 1–2, MNHN APH 4–5 (being figured) tian series, contrary to what occurs in the Oulad Abdoun and MNHN APH3, 6–16) as well as newly collected basin. This series begins with a plastic clay level that corre- vertebrae (OCP DEK ⁄ GE 500-535, OCP DEK ⁄ GE 537- sponds to a reference level in the Ganntour basin, followed 646), and includes three articulated portions of the verte- by 11-m thick unnamed bed, then troughs B to F. bral column (sometimes with ribs): OCP DEK ⁄ GE 95, One of the main characteristics of these Phosphates is OCP DEK ⁄ GE 418 and OCP DEK ⁄ GE 536. their extreme richness in fossil vertebrate remains of latest Cretaceous–Palaeogene age, known since the pioneer Methods. To complete the anatomical observations, vari- works of Arambourg (1952). Since 1997, an active ous measurements (Rage 2001; Houssaye et al. 2011) were French–Moroccan scientific collaboration (Acknowledge- taken for the vertebrae when the degree of preservation ments) has permitted new palaeontological field cam- was sufficient: WPr, width across the articular facets of paigns, which has resulted in an abundant collection from the prezygapophyses; WPa, maximal width across the both Maastrichtian and Palaeogene deposits of new verte- articular facets of the paradiapophyses; WPt, width across brate remains (including articulated skeletons) belonging the articular facets of the postzygapophyses; WIC, width to selachians (Noubhani and Cappetta 1997), bony fishes of interzygapophyseal constriction; CL, centrum length; (Cavin et al. 2000), marine and continental sauropsids CTW, cotyle width. (see Bardet et al. 2010 for bibliographical details), as well Five vertebrae (OCP DEK-GE 642–646) illustrating var- as continental mammals (Gheerbrant et al. 2003). These ious positions along the vertebral column (cf. Table 1) new discoveries significantly improve our knowledge of were used for histological sections. They were sectioned these vertebrate assemblages, which were either previously using standard techniques (Houssaye et al. 2008) along unknown or represented only by fragmentary or isolated their mid-sagittal and neutral transverse (sensu Buffre´nil remains (Arambourg 1952). et al. 2008) planes. The sections were examined micro- The specimens, on which the original description of scopically at low- and medium-power magnifications