Forces Driving Angiosperm Divergence III

CO2 theory

120-80mya break up of Pangaea, lots of volcanic activity- world CO2 levels increase. Cause increase biomass of plants. More biomass = more competition. In order to survive angiosperms ancestors shortened life cycle to be competitive. Quicker turn over of generations = speeds up evolution and increases diversification. Angiosperms use this opportunity to become dominant.

Gynecological Theory

Genecology: study of genetic composition in relation to the enviroment. Angiosperms is successful, because they possessed the genes needed to be morphologically, physiologically and ecologically adaptable. Supported by the genetic studies of Arabidopsis thaliana. Research suggests Angiosperms underwent 3 major duplications of their genomes (polyploidy).

3 major duplications

1. Late Jurassic/Early Cretaceous in basal angiosperms c.140mya. Before evolution of the monocots. Correlates with 1st proper flowers and subsequent mass radiation.

2. Cretacous (145-65mya) c.118mya correlate with the first triporate pollen - Eudicots. May explain why eudicots became so diverse.

3. Occurred different times in various lineages. 5.97mya.

Xylem evolution

Taylor (2004) attributed the Cretaceous diversification of angiosperms to evolution of better xylem vessels which was composed of vessel elements and tracheids.

As angiosperms moved out of dark damp places into sunnier dryer conditions. Evolved more efficient xylem to cope with new sunnier and drier habitats.

End of Cretaceous

The ancestors of all major present day clades were present. 66-65mya. Diversification of basal angiosperms, magnoliids and monocots 130-125 mya. Eudicots diversified 118mya. Split of Rosid’s and Asterids 117-70mya.

Angiosperms were a diverse group of global dispersed weedy plants but with restricted distribution - mostly along water courses or near bodies of water. Did not have ecological dominance at the time, only occurred after Cretaceous (KT) extinction. Only in the last 60 my have they begun to radiate and dominate