GUODUNITES, A LOW-PALAEOLATITUDE AND TRANS-PANTHALASSIC SMITHIAN (EARLY TRIASSIC) AMMONOID GENUS

Abstract:  Based on new, bed-rock controlled material from Oman and Utah, USA, the Early Triassic genus Guodunites , which was recently erected on the basis of scarce specimens from northwestern Guangxi, South China, is now shown to be a representative of Proptychitidae. This solves the question of the previously unknown phylogenetic affinity of this genus. The genus is restricted to the late middle Smithian, and to date, its biogeographical distribution comprises Oman, South China and Utah, thus indicating an essentially low palaeolatitudinal distribution during the Early Triassic. Its palaeobiogeographical distribution further strengthens the existence of significant equatorial faunal exchanges between both sides of the Panthalassa at that time. It also suggests that, in addition to the potential stepping stones represented by Panthalassic terranes, vigorous equatorial oceanic currents must have contributed largely to the dispersal of ammonoids during such time intervals.