[D] Atlasaurus imelakei [Su] [sG] [T]
Monbaron, Russell, & Taquet, 1999
Jurassic Middle Bathonian Callovian
Saurischia Sauropodomorpha Sauropoda ?Brachiosauridae
Tilougguit Formation, Wawmda, Azilal province, High Atlas, Morocco
Genus - Typespecies - Skull
The nearly complete skeleton of a large sauropod discovered at Wawmda (High Central Atlas of Morocco) in strata of Bathonian-Callovian age represents a new taxon: Atlasaurus imelakei n.g., n.sp.
The sauropod appears to be closer to Brachiosaurus than any other known known sauropod, but possesses (relative to the length of the dorsal vertebral column) a larger skull, shorter neck, longer tail and more elongated limbs.
The presence of large sauropods of Middle Jurassic age is very important in understanding the history and the evolution of these Mesozoic giants.
Etymology: Atlasaurus: Atlas, the mountain chain from Morocco and also Atlas, the giant Imelake: (arabic) giant. The description of the specimen is abridged and preliminary, and a fuller description will appear elsewhere.
Diagnosis: Autapomorphies include: supratemporal fenestra twice as wide as long (140 by 70 mm) not visible in lateral perspective; combined width of paroccipital processes 48 % of estimated length of mandible; paroccipital processes extend horizontally at nearly right angles to long axis of skull; mandibular symphysis and dentary very shallow (symphyseal depth 116 % minimum depth of dentary, probably reversal from primitive state in sauropods); length of humerus 65 % of estimated length of dorsal series; length of ulna exceeds length of tibia by about 115 %.
In other known sauropods the supratemporal fenestra is more dilated anteroposteriorly, and the dorsal margins of the fenestra slope laterally so that it is visible in lateral perspective; the paroccipital process is markedly inclined ventrodistally, posteroventrally or both; the combined width of the processes is less than 48 %of the length of the mandible (table I); the ratio between the symphyseal depth and the minimum depth of the dentary is at least 150 % (Wilson and Sereno, 1998); the humerus is shorter relative to the estimated length of the dorsal series; and the ulna does not surpass the tibia so greatly in length (McIntosh, 1990, p. 377). Features in the skeletal anatomy of Atlasaurus imelakei distinguish it from all other Jurassic sauropods (for brief descriptions and references to other Jurassic sauropod taxa, see McIntosh, 1990).