A new crocodylian, Dongnanosuchus hsui n. gen. n. sp., is described mainly based on four well-preserved skulls from the Eocene Youganwo Formation of the Maoming Basin, southeastern China. It is an alligatoroid and phylogenetically nested within the Orientalosuchina. Dongnanosuchus hsui n. gen. n. sp. differs from all other orientalosuchines primarily in certain features of the skull: (1) a preorbital ridge connects posteriorly with the dorsal orbital rim and a ridge around the anteroventral margin of the orbit, (2) the palatine is short and does not reach the posterior border of the suborbital fenestra, (3) the external mandibular fenestra is closed, and (4) the splenial joins the formation of the mandibular symphysis. The discovery of Dongnanosuchus hsui n. gen. n. sp. confirms the monophyly and North American origin of the Orientalosuchina but suggests that the clade dispersed to Asia via Beringia after diverging from the mainline rather than a sub-lineage of the Alligatoroidea in the Late Cretaceous.

UUID: http://zoobank.org/f8ca22f1-6323-462e-bf32-03c6a164c82e.

Rock-art, despite much ingenious effort (e.g., among many, Watchman et al. 1997), remains difficult to date by absolute methods, so relative dating has a central importance much as applied to dirt archaeology in the era before routine radiometric dating. It is sound relative dating which will show just what the entities are to which absolute dates may be connected. The first basis for relative dating is the determination of sequence: what motifs done by which techniques in which materials precede and follow each other; and the first basis for sequence is physical superposition, in which one figure plainly overlies another or - in the case of rock-engravings - one figure clearly cuts through another. But often figures do not cut or superpose each other so no relation of sequence exists: and sometimes figures are cut through each other without sequence being clear, or are so much overpainted that the older figures are impossible to discern.