Thursday, October 17, 2013

So Where is the Evolution in Arthropod Nervous Systems?

Sorry to keep posting evolution articles on what is primarily a blog about Arkansas politics.  If I had more time I could probably start a completely separate blog on new science discovers which contradict the macro-evolutionary hypothesis.   I ask that you just scroll to the next one if this is not your area of interest.

Scientists used some very clever techniques to coax the outlines of the nervous system from a 520 million year old fossil nick-named "mega-claw".   This was near the Cambrian Explosion, which is when a vast array of animal forms suddenly appear in the fossil record.  The date for the CE has been calculated to be 543 million years ago.  Scientists have been trying to talk their way around the implications of this event for decades.

What they were trying to determine was where the nervous system of Mega-claw fit into the subphylums of the Arthropods.  Was it more crustacean, or arachnid, or something in-between.    Here was what they found....
"We now know that the megacheirans had central nervous systems very similar to today's horseshoe crabs and scorpions," 
Arachnids then.  To be more specific...

Comparing the outline of the fossil nervous system to nervous systems of horseshoe crabs and scorpions left no doubt that 520-million year-old Alalcomenaeus was a member of the chelicerates. 
Specifically, the fossil shows the typical hallmarks of the brains found in scorpions and spiders: Three clusters of nerve cells known as ganglia fused together as a brain also fused with some of the animal's body ganglia. This differs from crustaceans where ganglia are further apart and connected by long nerves, like the rungs of a rope ladder. 
Other diagnostic features include the forward position of the gut opening in the brain and the arrangement of optic centers outside and inside the brain supplied by two pairs of eyes, just like in horseshoe crabs. 
To make the analysis more robust, the researchers then added these features to an existing catalog of about 150 characteristics used in constructing evolutionary relationships among arthropods based on neuroanatomical features. 
"Greg plugged these characteristics into a computer-based cladistic analysis to ask, 'where does this fossil appear in a relational tree?'" Strausfeld said. "Our fossil of Alalcomenaeus came out with the modern chelicerates."
  So Mega-claw has a nervous system like an arachnid, and not like a crustacean.  It was not a mix between the two.   They had previously done similar research with another fossil, and found that its nervous system was set up just like that of crustaceans.
Less than a year ago, the same research team published the discovery of a fossilized brain in the 520 million year-old fossilFuxianhuia protensa, showing unexpected similarity to the complex brain of a modern crustacean.
So I ask you my friends, with regards to the central nervous system, where is the evolution?  We see the same set up in these 520 million years old fossils as we see in creatures alive today.  Animals with nervous systems just like arachnids and those with nervous systems just like crustaceans were walking side by side 520 million years ago.  Where is the common ancestor between these two groups?   If there really was one, you might expect the central nervous systems of 520 million year old fossils to be more like a cross between the two.

Or as one of the scientists put it..
 "Our new find is exciting because it shows that mandibulates (to which crustaceans belong) and chelicerates were already present as two distinct evolutionary trajectories 520 million years ago, which means their common ancestor must have existed much deeper in time," 
 With the Cambrian Explosion not much before that, that time does not seem to be available.   They expect us to believe that the two types of nervous systems did 100% of their evolving in the short time available (perhaps 23 million years) before these two fossils existed and then stayed essentially unchanged for 520 million years.   And this is not the only example of this sort of phenomenon.   My issue is not that they have found in this case two wholly developed systems where they should find intermediaries, my issue is that this is the norm.  This is virtually all that they ever find.  Every time they do deep research like this where macroevolution would expect to find an intermediate system they find two fully differentiated systems.   Or they find something that they thought came along much later was already fully developed at an early date.


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