22 nd International Senckenberg Conference 110 Talar morphology of azibiids, strepsirhine-related primates from the Eocene of Algeria LAURENT MARIVAUX 1 , RODOLPHE TABUCE 1 , RENAUD LEBRUN 1 , ANTHONY RAVEL 1 , MOHAMMED ADACI 2 , M’HAMMED MAHBOUBI 3 , MUSTAPHA BENSALAH 2 1 Institut des Sciences de l’Évolution (UMR-CNRS 5554), C.c. 64, Université Montpellier, 2 Place Eugène Bataillon, F-34095 Montpellier Cedex 05, France, Laurent.Marivaux@univ-montp2.fr; 2 Laboratoire de recherche n°25, Département des Sciences de la Terre, Université Abou Bekr Belkaïd, B.P. 119 Tlemcen 13000, Algeria; 3 Laboratoire de Paléontologie stratigraphique et Paléoenvironnement, Université d’Oran, B.P. 1524 El M'naouer, Oran 31000, Algeria. Over the past decades, the Afrocentric model for anthropoid primate origins has relied upon the >45- Myr-old fossil Algeripithecus minutus from Algeria (Gour Lazib, Hammada du Dra), which was widely acknowledged to be one of the oldest known anthro- poids (Godinot and Mahboubi, 1992, 1994; Beard, 2002; Seiffert et al., 2005). However, very recent discoveries of more nearly complete fossils of Algeripithecus, as well as of Azibius trerki, another primate of uncertain affinity (formerly; Sudre, 1975) from the same rock unit of Algeria, strongly suggest that these two primates are closely related and, in any case, phylogenetically remote from the clade Anthropoidea. Algeripithecus and Azibius make up the family Azibiidae and represent the earliest off- shoots of an Afro-Arabian strepsirhine clade that em- braces extant toothcombed primates (lemurs, lorises and galagos) and their fossil relatives (Tabuce et al., 2009). This new fossil-based interpretation strongly challenges the role of Africa as the ancestral home- land for anthropoids, yet, at the same time, reveals an ancient African origin for crown strepsirhines. Beyond these highly critical phylogenetic implications, these fossils have also highlighted some aspects of the paleobiology of these ancient African primates. The new paleontological evidence assembled has indeed revealed that azibiids were highly dentally specialized (e.g., high-crowned posterior premolars forming a blade-like structure, and pronounced buno- donty of molars with a large hypocone), appearing somewhat as an aberrant group of stem strepsirhines having strong dietary specializations. In addition, cranial remains (fragments of maxillary-bearing teeth) referred to Azibius trerki have also provided anatomi- cal evidence suggesting nocturnality in this taxon. However, information regarding the locomotor behav- iour of these primates has so far remained elusive because of a lack of primate postcranial evidence in the Gour Lazib fossil record. Our continuing long-standing field efforts in the primate-bearing localities of the Gour Lazib area have finally led to the recovery of postcranial remains of primates. Two ankle bones of distinct size (the small UM/HGL50-466, and the large UM/HGL50-467) have been sorted after acid treatment of the indurated sediments of the HGL-50 layer located on the Glib Zegdou outlier. The HGL-50 locality is famous for having yielded several dental remains of primates, including Algeripithecus minutus, Azibius trerki, and a new species of cf. Azibius. The last is documented by isolated upper and lower teeth (unpublished mate- rial), which are about three times larger than their counterparts in A. trerki. The two new primate tali from HGL-50 are reasonably well preserved, lacking any apparent post-mortem distortion. However, the numerous local breaks and the exposure of the trabecular bone structure in several talar regions (cortical bone eroded) indicate that these tali were damaged during deposition and/or fossilization processes. Despite the clear difference in size between UM/HGL50-466 and UM/HGL50-467, these two tarsal elements are virtually comparable in terms of structure. In overall proportions, both tali are mark- edly narrow relative to their length, and moderately tall in medial or lateral view. The length of their talar neck plus head is about half of total talar length, and clearly longer than the length of the trochlea. Their necks are only very slightly deflected medially (17– 18°) relative to the anteroposterior axis of the troch- lea, a condition which strongly contrasts with the very medially angled talar neck observed in practically all extinct and extant anthropoid primates. The overall proportions and the low degree of neck deviation of these two new tali are generally observed in certain modern strepsirhine families, particularly in the Cheirogaleidae (e.g., Allocebus, Microcebus). Modern tarsiids (i.e., Tarsius) exhibit also a weak neck deviation, but differ in overall proportions. In anterior view, the heads appear ovoid in shape, being wider than high, with their long axis oriented mediolaterally relative to the dorsal plane of the trochlea. On UM/HGL50-467, the trochlea is only moderately grooved, displaying rounded and symmetrical medial and lateral trochlear rims. On this talus, the medial trochlear rim extends slightly farther distally onto the talar neck compared with the distal end of the lateral rim, a condition not found in UM/HGL50-466. Proxi- mally, the two tali bear a prominent trochlear shelf, which is characteristic of most extant strepsirhines and Paleogene adapiforms, but also, to a lesser extent, of omomyids, omomyiforms and eosimiids anthropoids. A set of talar features has proven to be useful in reconstructing higher-level primate phylo- geny (e.g., Gebo, 1988; Beard et al., 1988; Dagosto and Gebo, 1994). Interestingly, UM/HGL50-466 and UM/HGL50-467 display a suite of derived morpho- logical characteristics which are otherwise found only in strepsirhine primates. These features include a lateral position on the posterior trochlea of the groove for the flexor hallucis longus muscle, the lateral talo-