New anatomical data and phylogenetic relationships of<i>Chebsaurus algeriensis</i>(Dinosauria, Sauropoda) from the Middle Jurassic of Algeria

Abstract

New osteological details of the sauropod Chebsaurus algeriensis from the Middle Jurassic Aïssa formation of the Naama Province, Algeria, are presented. The described material belongs to two juvenile individuals. Recent field work has provided new cranial and post-cranial material. This new material presents a combination of plesiomorphic and apomorphic eusauropod characters adding more data to the skull and the post-cranial skeletal morphology. A phylogenetic analysis (237 characters, 39 taxa: 16 parsimonious trees of 479 steps, CI = 0.53, RI = 0.73) (Läng 2008 Läng E. 2008. Les cétiosaures (Dinosauria, Sauropoda) et les sauropodes du Jurassique moyen: révision systématique, nouvelles découvertes et implications phylogénétiques [Dissertation]. [Paris]: Muséum National d'Histoire Naturelle, 2 Volumes, 638 pp. [Google Scholar]) indicates an unsolved phylogenetic position of Chebsaurus within the non-neosauropod Eusauropoda. Indeed, Chebsaurus is positioned in a multifurcation with Middle Jurassic ‘cetiosaurids’ Lapparentosaurus madagascariensis, Ferganasaurus verzilini, ?Cetiosaurus mogrebiensis and Cetiosaurus oxoniensis from Oxford. This polytomy could be explained by numerous missing data and also by the incongruence of the informative characters for the Middle Jurassic basal eusauropods. The latter could result from an evolutive radiation that might have succeeded the extinction at the end of the Early Jurassic (Pliensbachian–Toarcian) and/or the Pangea break-up.