Wednesday, March 7, 2012

Trilobite evolution - Pelagic morphology

Proetida Carolinites leisurely swimming upside down!
Sam Gon III website

Well, just when we thought we have it figured out... normal eyes (more about them later), no need for eyes, so skip them.

And then we get these Big Eye Carolinites as example of  the opposite of reduction of size ... Pelagic morphology.

Nature does not seem to be such a simplistic thing after all - not even at the very beginning of the history of life upon Earth!

Sam does not even try to explain, only notes the fact "There are a number of trilobites that have developed extremely large eyes and elongate, streamlined body shape associated with swimming in the photic water column."

The photic zone or euphotic zone (Greek for "well lit”: εὖ “good” + φῶς “light") is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur.

The depth of the photic zone can be affected greatly by seasonal turbidity. It extends from the atmosphere-water interface downwards to a depth where light intensity falls to one percent of that at the surface, called the euphotic depth.

Accordingly, its thickness varies widely on the extent of light attenuation in the water column. Typical euphotic depths vary from only a few centimetres in highly turbid eutrophic lakes, to around 200 metres in the open ocean.

Ah, finally I caught Sam at the scene of the crime that I have blamed evolutionary biologists all along!

Note the active verb " trilobites that have developed extremely large eyes and..."

As if one honourable trilobite decided "now I want to develop big eyes and elongate body shape so that I can swim better in these lovely Cambrian oceans".

As if you could say "now I want to grow red hair because it attracts the kind of men I like."


This active form where an organism actively evolves something for some purpose is often present in professional texts and is IMHO highly unprofessional as evolutionary theory emphasizes the importance of environment and selection, not the active action of an organism itself to evolve.

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