Where did Angiosperms First Evolve I

Two ways

To establish where angiosperms originated

1. Fossils

2. Distribution of extant basal angiosperm

Fossil evidence pollen

Microfossil. 1st definite angiosperms fossils. Sporopollenin= forms the exine layer. One of the most resistant material in the plant kingdom.

Pollen dated ~130 mya found in Israel. Basal (magnoliid) type- monosulcate. Pollen also similar to Chloranthus fairly common.

Fossil evidence

Small fossil flowers and leaves found in eastern United States (potomac) and Portugal (150 different species). These sites are linked by the fact that they followed what was the rift valley between Africa, Europe and the Americas. Dates to Triassic.

Cretaceous at c.110mya around North Atlantic. This area being situated over the tropics was warm and wet. The type of habitat in which angiosperms are believed to have evolved. Spread out from rift valley.

Tropics and subtropics

Quaternary ice ages: global climate had fluctuated greatly 3 mys, leading to the recent major ice ages consequence for biota. Major changes in distribution shifts in boreal, tempreture and tropical zones. LGM 8 degrees Celsius.

Causes of quaternary ice age

1. Change in orbital eccentricity of Earth: orbital changes. Occur on a cycle of about 100000 years.

2. Inclination/ tilt of Earth's axis: varies between 22-24.5 degrees in a cycle.

3. Procession of the equinoxes: wobbles in the Earths rotation axis. Have a periodicity of 26 000 years.

Rift valley origin

More complex. Early Cretaceous pollen also found in China. Exact age not certain, could be as old as 130 my. China- separated by some distance from the tropical rift valley.