Evolution illustrated by foraminifera 1

Natural Selection

The theory of evolution wants to explain how we - meaning all living organisms - came to be in all our complexity and variation. In a group of organisms the environmental conditions will favour some individuals while others will not reproduce as well. If heritable characters are the cause a shift in the frequency of these heritable characters within a population will occur after some generations. This process is called natural selection.

fossil Globigerina sp.
Italy, Pleistocene
Natural selection leads to specific foraminiferal faunas in specific environments

Open Sea offers little nutrition, which makes survival very difficult though competition is low and predators are rare. Many planktonic foraminifers use symbiont algae, who deliver energy through photosynthesis. In return they gives shelter for the little algae in its chambers, which need to be transparent, so that the sunlight may pass. Its globose construction allows up and downward drift in the watercolumn, probably needed to follow food, avoid predators and UV radiation.

recent Globigerinoides ruber from Mexican pacific ocean.

read the whole story at www.foraminifera.eu/evolution.html

Oligocene foraminifera from Atzendorf, Germany

Prof. Mueller, Geologisch - Palaeontologische Sammlung, University of Leipzig provided a sample from Atzendorf near Stassfurt, Germany. It dates back 30 mya to the Rupelian stage, lower Oligocene. Most foraminifera are small, below 500µm in size and lived benthic. An example is Bolivina fastigia seen to the left. See the whole collection at http://www.foraminifera.eu/atzendorf.html


Some planktonics (well preserved) are found, I classify them as Globigerina globularis (see image to the right. There are several Spiroplectinellas respresenting the agglutinating foraminifera.

I am not much familiar with faunal interpretation, but would interprete from the faunal composition: 5-10% planktonics indicate open waters, which correlate with the overall smaller sized benthonics.