The impact of extinct taxa on understanding the early evolution of Angiosperm clades: an example incorporating fossil reproductive structures of Saxifragales

摘要

A cladistic analysis was performed including five Cretaceous and 31 extant taxa within Saxifragales using a combination of molecular sequence and morphological data in order to elucidate the utility of extinct taxa in illuminating saxifragalean evolution. The results suggest that Saxifragales as well as most major infraordinal clades lack unambiguous morphological synapomorphies among the characters examined; that the major lineages of Saxifragales were distinct by ca. 90–70 Ma; and that the ca. 90 Ma taxa lack characteristic derived features present in modern taxa. General conclusions concerning the advantages of joint extinct-extant taxon phylogenetic analyses explored herein include: 1) Prediction of the morphological characters present in early members of a clade; 2) Determination of minimum ages for lineage divergences; 3) Resolution of the order in which synapomorphies may have evolved; and 4) Circumscription of the time interval during which synapomorphies may have evolved.