Article: An evolutionary sequence in Aratrisporites miospores from the Triassic of Queensland, Australia

Specimens of Aratrisporites, a miospore genus of probable lycopsid affinity, are common in some palynofloral assemblages of Early Triassic age, from the Rewan Formation of the Bowen Basin, Queensland. Study of numerous specimens from a sequence about 1710 m. thick supports the view that A. tenuispinosus developed, by increase in spine dimensions, from A. wollariemis. The observed development of this evolutionary sequence favours quantum speciation, rather than a gradualistic process, as the change from one species to the other takes place over a relatively short stratigraphic interval. It is unusual, in the palynological record, for specimens, showing an evolutionary transition between species, to be observed; reasons for their occurrence in this case are suggested.