LOWER DEVONIAN BIOSTRATIGRAPHY AND VERTEBRATES OF THE TONG-VAI VALLEY, VIETNAM

A new vertebrate assemblage is described from the base of the Khao Loc Formation at Tong Vai, Dong Van district, Ha Giang Province, Vietnam. It includes the galeaspid Polybranchiaspis liaojaoshanensis, two acan thothoracid placoderms, and the sarcopterygian Youngolepis praecursor. This assemblage is quite similar to that of the Xitun Formation of Yu nnan (Late Lianhuashanian to Early Nagaolingian) and can also be corre lated with the vertebrate faunas which occur at the base of the Bac Bu n Formation of the Bac Bo in Vietnam. New data on the morphology of P. liaojaoshanensis are provided on the basis of this material, with spe cial reference to the structure and ornamentation of the exoskeleton.