>
>
> I am not a trilobite expert, but I do teach undergrad paleontology on
> occasion and what Jonathon said about trilobite cuticles did not ring
> right so I looked it up in Clarkson (the text I use). He says that
> unlike most arthropod skeletons that are chitin and sometimes
> mineralized the cuticle is "largely of low magnesium calcite ..
> arranged in microcrystalline needles. .. they are, "set in an
> organic base whose nature has yet to be determined" (p.346) but he
> indicates that chitin has NOT been detected.
>
> If I am not mistaken the nature of their cuticle may be why they have
> unusual calcite lenses with interesting corrections for the nature of
> calcite. As far as I can recall no other invertebrates use calcite
> lenses. I don't know how that helps the argument but it means that
> going from a soft to hard exoskeleton could not be simple mineralization
> of a chitin's skeleton.
I stand (or sit) corrected! Obviously I should of written organic substrate rather than specify
chitin. My copy of Clarkson is in my university office 20 km away so I did not refer to it when I
wrote my post. With this correction I believe by statement about mineralisation of a previously
existing organic exoskeleton stands. As David Campbell points, the nether regions of trilobites were
un mineralised, with an organic exoskeleton.
A question for those more learned than I. My understanding was that all arthropods used chitin in the
exoskeleton, with varying degrees of calcite mineralisation. This is presumably why I mentioned chitin
in relation to trilos. Are there any arthropods which don't use chitin?
In Christ
Jonathan