Evolution of the agathioid lineage (Araucariaceae)

ESCAPA I.; WILF PETER; CATALANO SANTIAGO; ARI IGLESIAS; CÚNEO RUBEN

Mendoza

Congreso; 4th International Paleontological Congress; 2014

IANIGLA, CCT-CONICET Mendoza

The conifer family Araucariaceae has three extant genera: Araucaria and Agathis, both known since the 19th century, and Wollemia, a monotypic genus discovered twenty years ago in New South Wales. Araucarian genera have a primarily southern distribution, with most of the species endemically distributed in Australasia and southeast Asia, especially New Caledonia, Australia, New Guinea, Borneo, and New Zealand, and two species of the type genus Araucaria in South America. Morphological distinction among Araucaria, Wollemia, and Agathis is clear from numerous vegetative and reproductive features, such as the presence/absence of seed wings, scale ligule, and scale tissues covering the seeds. Araucaria has a diverse macrofossil record that shows a cosmopolitan distribution during the Mesozoic. On the other hand, fossil representatives of Wollemia and Agathis are rare and predominantly confined to compressions of fragmented vegetative organs from Australia and New Zealand. A number of endemism theories had been developed due to the apparent absence of Agathis macrofossils in other Gondwanan regions. However, a well preserved Agathis macrofossil species, as well as dispersed pollen identical to that found in Wollemia and some Agathis species (Dilwynites), have been recently described from the Paleogene of Patagonia, extending the past distribution of the genus greatly. Phylogenetic relationships among Araucariaceae have been recently inferred from a combination of morphological and molecular features, which strongly support the existence of an ?agathioid? clade whose living representatives are Agathis and Wollemia. In this presentation we discuss the origin and diversification of the ?agathioid? lineage, whose evolutionary history during the Mesozoic has been obscure per decades. Interestingly, although the fossil record indicates that the lineage of Araucaria achieved its modern morphology by the Early Mesozoic, new early Paleocene (Danian) vegetative and reproductive fossils from Patagonia indicate that the acquisition of the derived features of Agathis occurred much later and was not complete even by the early Paleocene. In this context, Araucariaceae may represent one of the best-understood and documented southern conifer families in terms of direct fossil evidence for the character evolution of its main lineages, representing a unique opportunity to test the validity of molecular estimates of divergence times.