Re: cambrian explosion

Glenn R. Morton (grmorton@waymark.net)
Fri, 21 Aug 1998 21:51:22 -0500

At 06:28 PM 8/21/98 -0700, Cliff Lundberg wrote:
>Glenn R. Morton wrote:
>
>> Once again, it isn't quite so suddenly. The first fossil chordates, are
>> invertebrates. These animals had a soft-tissue nerve cords running down
>> their back, but they had no actual backbone. Carroll says
>>
>> "None of the early vertebrate groups shows evidence of a bony internal
>> skeleton." Vertebrate Paleontology and Evolution p. 23
>
>How do you get into a vertebrate group without having vertebrae? There
>is confusion here regarding chordates and vertebrates, fueled by the
>widely held assumption that vertebrates sprang from a simpler chordate
>like amphioxus or tunicate larvae etc. The evidence for this is
>simple-to-complex chain-of-being phylogeny and recapitulation theory.
>I would venture to say that zero progress has been made in establishing
>this view in the last 100 years.

Cliff, I am citing the fossil data, not comparative anatomy.

>
>What has been established in the last 100 years is the principle of
>reduction and specialization of serial homologs. Vertebrate skeletons
>evolve through loss, distortion, and fusion of parts. This is contrary
>to the intuitions and hopes of simple-to-complex evolutionism, but it
>is fact. It's actually quite logical: random mutation generating a new
>skeletal segment in a halfway useful position, complete with
>complementary
>soft tissues, is unlikely. But random mutation simply throwing a monkey
>wrench into development, such that development is truncated and segments
>are distorted or lost, is perfectly reasonable.
>
>If one takes this principle seriously, one must theorize a sudden
>beginning in which a mass of identical segments begins functioning as
>one organism. Subsequent radiation and evolution would see this organism
>trimmed down to fit niches, rapidly at first, then more slowly.
>
>> It isn't taboo. Can you cite some evidence that the cambrian explosion
>> isn't being discussed?
>
>No, but I'll stick to my point that people love to battle over small
>particulars but are less comfortable addressing the biggest topic of
>all,
>the appearance of vertebrates.

Then you actually have no evidence to support your case. I would suggest
that you consult any good vertebrate paleo book to see them discussing
exactly what you say they don't discuss. Carroll that I cited is an
excellent source.

>
>> The fossil evidence clearly shows that invertebrate
>> chordates first appear followed by chordates with vertebrae.
>
>Vertebrates could have been a rare form, until enough time passed
>for their more complex morphology to be usefully harnessed. Only then
>would they proliferate and commence their domination.
>
>You don't accept simplistic simple-to-complex phylogeny. You don't
>accept
>recapitulation theory. So what is your basis for accepting the old
>amphioxus-to-vertebrate model and repudiating the established principle
>of reduction and specialization in the evolution of segmented organisms?

You sure jump to conclusions. I didn't say and haven't mentioned amphioxus
at all. And I cited paleontological data, not comparative anatomy.
Amphioxus is a modern animal and not the ancestor of the earliest chordates.

glenn

Adam, Apes and Anthropology
Foundation, Fall and Flood
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