A Pterodactyloid Pterosaur from the Upper Cretaceous Lapurr Sandstone, West Turkana, Kenya

An isolated pterosaurian caudal cervical (∼ postcervical) vertebra was recovered from the Upper Cretaceous Lapurr sandstone of West Turkana, northwestern Kenya. The vertebral centrum is short, wide, and dorsoventrally compressed. Although the specimen is lightly built similar to most pterosaurs, it is here referred to Pterodactyloidea and tentatively to the Azhdarchidae in that it lacks pneumatic features on both the centrum and neural arch. This represents one of the few pterosaurs recovered from the entirety of Afro-Arabia, the first pterosaur recovered from the Cretaceous of East Africa, and, significantly, a specimen that was recovered from fluvial deposits rather than the near-shore marine setting typical of most pterosaur discoveries.


INTRODUCTION
Upper Cretaceous terrestrial/freshwater deposits from continental Africa are rare (Haughton 1963, Dingle et al. 1983, Mateer et al. 1992) and limited to a handful of geographically-restricted sites.Despite this paucity of terrestrial sequences, a number of paleobiogeographic hypotheses have been proposed to account for the distribution of terrestrial vertebrate groups (e.g., dinosaurs) on former Gondwanan landmasses during the Late Cretaceous (∼100 to 65 mya) (see Krause et al. 2006 for a recent summary).This period is of significance in that it coincides with the most active fragmentation of the Gondwanan supercontinent (Scotese 2001), an event that likely influenced the evolution and spatial distribution of resident biotas through speciation, dispersal, and extinction events.O' Connor et al. (2006) discussed limitations for conducting supercontinent-level paleobiogeographic analysis in the face of an abundance of missing data, framing the most obvious deficiency for Gondwananwide inferences as the 'African Gap' during the Late Cretaceous Period.
Within this general context then, it is not surprising that the fossil record of the lightly-built pterosaurs from Afro-Arabia is limited to a handful of mostly isolated skeletal and dental remains (e.g., Reck 1931, Swinton 1948, Galton 1980, Monteillet et al. 1982, Sigogneau-Russell et al. 1998, Unwin and Heinrich 1999, Mader and Kellner 1999, Wellnhofer and Buffetaut 1999, Benton et al. 2000, Barrett et al. 2008, Costa and Kellner 2009).Exceptions to these isolated discoveries include (1) the Maastrichtian azhdarchid Phosphatodraco, consisting of a semi-articulated series of five cervical vertebrae recovered from the Oulad Abdoun Phosphatic Basin in Morocco (Pereda Suberbiola et al. 2003; also see Kellner 2010) and (2) a partial pteranodontoid forelimb from the Cenomanian Hâqel Lagerstätte in Lebanon (Dalla Vecchia et al. 2001).
Recent field research in the Lapurr sandstone [Turkana Grits] in West Turkana, northwestern Kenya (Fig. 1), has yielded a number of new Late Cretaceous vertebrates (Sertich et al. 2005(Sertich et al. , 2006)).Included among the archosaurs are multiple saurischian dinosaurs, crocodyliforms, and the pterosaur vertebra detailed in this report.This represents the first pterosaur reported from the Late Cretaceous of East Africa and one of the few pterosaurs from the continent recovered from a fluvial depositional system.
Locality and horizon -The specimen described herein was recovered from the Lapurr sandstone, "Turkana Grits" (Upper Cretaceous) exposed in the Lapurr Range on the west side of Lake Turkana, northwestern Kenya (Fig. 1).The Lapurr sandstone is a succession of fine to coarse arkosic sandstones of indeterminate age resting noncomformably over Precambrian metamorphic basement and overlain by Oligocene basalts.Fluvial deposition of the Lapurr sandstone is likely related to the development of the Cenomanian-Paleogene Anza Rift system (Bosworth and Morley 1994, Morley et al. 1999, Tiercelin et al. 2004) Diagnosis -KNM-WT 47893 is here referred to Azhdarchidae on the basis of the following combination of features: a short, high vertebra lacking a pneumatic foramen on the lateral surface of the centrum; a neural arch attached to the cranial half of the centrum.

DESCRIPTION
KNM-WT 47893 is a caudal cervical vertebra consisting of a fused centrum and neural arch.The vertebra is heavily abraded and lacks cortex over most of its surface, instead revealing the complex meshwork of widely-spaced trabecular bone characteristic of most pterodactyloids (Fig. 2).The centrum is short and low, with overall proportions characteristic of the caudalmost cervical or cranialmost, non-notarial dorsal vertebrae.The centrum is 34.2 mm long and 29.0 mm wide at mid-central length.
The vertebral height is 36.8mm measured from the ventral surface of the centrum to the preserved extent of the neural spine.The centrum is procoelous, dorsoventrally-compressed, and exhibits a distinctly convex condyle on the caudal surface.The reniform condyle extends past the caudal extent of the postzygapophysis (Fig. 2C).The cotyle is moderately concave, does not extend past the cranial extent of the prezygapophysis, and exhibits a slight median hypapophysis at its cranioventral margin (Fig. 2F).The centrum lacks a lateral pneumatic foramen typical of most non-azhdarchid pterodactyloids (Kellner 2003, Averianov 2007; also, see Andres and Ji 2008).There is no evidence of a postexapophysis, indicating that it was either not preserved or that this vertebra is from a more caudal position such that its absence would be expected.The attachment of the pedicle is restricted to the cranial half of the centrum, resulting in a modest space between the postzygapophysis and the dorsal surface of the centrum (Fig. 2A).This is characteristic of caudal cervical vertebrae (∼C8-C9) in many pterodactyloid taxa.The neural canal is large (22% of centrum height) and round in cross-section when viewed caudally.Poor preservation of the cranial end of the vertebra precludes a direct determination of neural canal size and shape.Pneumatic foramina adjacent to the neural canal are not present on either end of the vertebra.Whereas the ovoid postzygapophyseal facet is oriented at approximately 45 degrees relative to the horizontal, poor preservation prevents any specific determination of prezygapophyseal morphology.A small, craniocaudally-restricted transverse process is preserved at the cranial end of the neural arch on left side only (Fig. 2E); however, incomplete preservation of the cortical surface renders the identification of a distinct diapophyseal facet (as would be present on a cranial dorsal vertebra) incomplete.The craniocaudally-restricted neural spine slopes caudodorsally, but this may also reflect the state of preservation, and a modest postspinal fossa is present.Due to extreme weathering, it is unclear to what extent the transverse process and neural spine were developed.

DISCUSSION
The presence of a post-Cenomanian azhdarchid pterosaur in East Africa is consistent with the temporal range of the clade, which minimally spans all of the Late Cretaceous (Unwin 2003(Unwin , 2006) ) or from the latest Jurassic through the end of the Cretaceous (Kellner 2003), depending on which classification scheme is used.KNM-WT 47893 compares favorably with an azhdarchid, pre-notarial dorsal vertebra (ZIN PH 54/53 [Paleoherpetological Collection of the Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia]) recovered from the Late Cretaceous (Turonian-Coniacian) Tyul'keli locality in Kazakhstan (Averianov 2007).However, KNM-WT 47893 differs in having a centrum that is dorsoventrally compressed relative to ZIN PH 54/53.The general organization of the neural arch relative to the centrum (e.g., a pedicle attached along the cranial half of the centrum) indicates the specimen is positioned within the caudal-most cervical or cranial-most (i.e., pre-notarial) dorsal series (Howse 1986).Moreover, the presence of a reduced hypapophysis further suggests a caudal cervical position for the vertebra.With these characteristics taken together, we have chosen to classify KNM-WT 47893 as a caudal cervical vertebra until additional materials of the Kenyan form are recovered.
The recovery of pterosaur remains from the Late Cretaceous of Kenya is significant for a number of reasons.First, the Afro-Arabian record of pterosaurs is extremely sparse, consisting mostly of isolated bones and teeth from a range of Cretaceous sites in Morocco (Kellner and Mader 1996, 1997, Sigogneau-Russell et al. 1998, Wellnhofer and Buffetaut 1999, Knoll 2000).Notable exceptions among the fragmentary Moroccan discoveries are (1) the rostral portion of an anhanguerid upper jaw (Mader and Kellner 1999), (2) an associated series of five cervical vertebrae that have been referred to the Azhdarchidae (Pereda Suberbiola et al. 2003; although see Kellner 2010 for a comment on the interpretation of this specimen), and (3) a fused mandibular symphysis recently referred to Azhdarchidae (Ibrahim et al. 2010).
Other occurrences from the African continent include isolated elements from the Upper Jurassic Tendaguru Series in Tanzania (Reck 1931, Galton 1980, Unwin and Heinrich 1999, Kellner et al. 2007, Costa and Kellner 2009), an ornithocheirid metacarpal from Cenomanian-Turonian deposits in the Democratic Republic of Congo (Swinton 1948, Monteillet et al. 1982), a cervical vertebra and partial tibia from Campanian-Maastrichtian sequences in Senegal (Monteillet et al. 1982), and an isolated tooth from the Albian of Tunisia (Benton et al. 2000).Other pterosaur material from the then con-tiguous portion of what is now westernmost Asia (e.g., Jordan, Israel, etc.) include a pterodactyloid hind limb from the Cenomanian of Israel (Tchernov et al. 1996), cranial endocasts referred to azhdarchids (Lewy et al. 1993), and limited materials of the azhdarchid Arambourgiania from the Maastrichtian of Jordan (Arambourg 1954, Frey andMartill 1996).

CONCLUSION
The discovery of a new pterydactyloid pterosaur with azhdarchoid affinities from the Late Cretaceous of Kenya, although not unexpected at the continent level, adds a novel datum to a large region of Afro-Arabia.Perhaps most significant is the fact that KNM-WT 47893 was recovered from the fluvial Lapurr sandstone in the Turkana Grits, rather than from marine phosphate units as is typically the case for the vast majority of Afro-Arabian pterosaurs.Additional fieldwork in the Lapurr sandstone is currently underway and will no doubt continue to add important new data to the extremely sparse Late Cretaceous vertebrate record of Afro-Arabia.Palavras-chave: Pterosauria, Pterodactyloidea, África, Quênia, Cretáceo Superior.

Fig. 1 -
Fig. 1 -Map showing the location of the Lapurr sandstone exposures in northwestern Kenya and the locality (star) from which the pterosaur vertebra here detailed was recovered.