>The discovery of the 2 1/2-inch fossils suggests that vertebrates - animals
>with primitive spines or backbones - had already undergone considerable
>evolution by the Cambrian epoch, from about 490 million to 545 million years
>ago.
If they're fully formed vertebrates, it seems an understatement to say that
they had undergone considerable evolution. And I wonder what is meant
by 'primitive'. The use of the term 'primitive spine' is confusing. A notochord
is a 'primitive spine' in much of the literature. And of course the primary
definition of 'spine' is 'a pointed outgrowth' or some such.
>Morris said the latest find means that ''the so-called Cambrian explosion was
>more abrupt and dramatic than we thought.''
But still 'so-called!'
>However, Desmond Collins, a paleontologist at the Royal Ontario Museum in
>Toronto, said it is too soon to say if the history of early evolution must be
>rewritten. He pointed out that no similar specimens have been uncovered in
>the same area, where tens of thousands of fossils have been removed since the
>field was discovered in the early 1900s.
I would think that the number of similar specimens uncovered would be
irrelevant to the issue. But I'm not thinking like a professional curator.
>''Why is there so little fossil record?'' he asked.
Is he asking, 'why is it hard to find things that were buried 600 million
years ago?' Or is he asking 'why doesn't evolution begin with
worldwide populations?'
>They argue that the fossils are clearly early agnathans, a type of jawless
>fish that includes the modern lamprey and hagfish. They point to clear signs
>of zigzag muscle patterns and gill structures - both characteristics of
>modern fish. One fossil shows marks of an early spine.
Again, what makes a spine 'early'?
>Morris said the two ancient agnathans appear quite evolved. He suggested that
>the first vertebrates must have developed much earlier, perhaps 555 million
>years ago or more.
That doesn't seem much earlier, and who knows what he bases this on,
other than an earnest desire to see a pattern of gradual evolution.
I guess the point is that we have a long way to go before we are thinking
clearly about the Cambrian explosion.
Anybody have a link to pictures of the fossils?
--Cliff Lundberg ~ San Francisco ~ cliff@noe.com