F Rosa Rubicondior: Transitional Spiders and Nervous Scorpions

Friday 18 October 2013

Transitional Spiders and Nervous Scorpions

BBC News - Big clawed fossil had spider-like brain

Here's another one of those 'non-existent' intermediate fossils that creationists keep telling us about.

Admittedly, this isn't intermediate between a human and an ape or between one human species and another - which are what most creationists seem to think evolution is all about. This one is intermediate between two major divisions of the arachnida, the spiders or arachnids and the scorpions or dromopoda. This class also includes the horseshoe crabs, one of those 'living' fossils' creationists love because they imagine they prove evolution didn't happen.

Arthropods, or jointed legged, creatures include insects, crabs, shrimps, barnacles, lobsters, millipedes and several other marine and terrestrial invertebrates including the extinct trilobites. They all have a more-or-less hard exoskeleton composed of chitin and segmented bodies with pairs of appendages used for walking, swimming and, in the case of insects, flight. These appendages have also evolved to become mouthparts. This particular specimen is from 520 million years ago and is of one of an extinct group of arthropods known colloquially as the "great appendage" arthropods, which have large claw-like appendages on their heads. It was discovered in South China and is part of the segmented Alalcomenaeus genus.

The nervous systems of related phyla tend to be similar with the differences reflecting the divisions of the phylum into classes and orders, so studying the nervous systems of living creatures can help establish their evolutionary relationships. However, this method of classification is not normally available with fossils because nerve tissue, like all soft tissues, does not fossilise so readily as the hard body-parts.

But, using a new technique with a CT scanner and 3D software, researchers were able to see the basic structure of the nervous system and compare it to that of other arthropods. It was clear that this species was from a group that were ancestral to both the spiders and the scorpions and its nervous system also bore many similarities with the nervous system of larval forms of the horseshoe crabs.

It is hoped that this technique will now enable the evolutionary relationship of other arthropods to be worked out, so filling in another small area of the jigsaw puzzle of evolution.

And still no fossil has yet been found which is inconsistent with Darwin's and Wallace's theory of descent with modification or with the neo-Darwinian gene-based theory of evolution. Had one ever been found, I wonder how many creationists would suddenly have become convinced of the soundness of the scientific method and of the irrefutable nature of solid evidence.

'via Blog this'

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