Re: [asa] Transitions

From: D. F. Siemens, Jr. <>
Date: Thu Dec 07 2006 - 14:14:30 EST

On Thu, 07 Dec 2006 10:19:29 -0600 "James Mahaffy" <>
> Keith or David might disagree, however I would say we just have not
> found a lot more transitional fossils in the invertebrate record.
> Yes
> you can make a case for finding some more "vertebrate transitions"
> such
> as the whale or dinosaurs with "feathers"
> However, we have a decent enough fossil record for the
> invertebrates
> and the groups still tend to appear without transitions in the
> fossil
> record. A similar pattern holds for angiosperms that show a great
> radiation in the Cretaceous without good intermediate fossils. Of
> course most phylogenies or cladograms are based on living groups
> without
> much reference to fossils.

I'm not a paleontologist, but I'm going to stick my neck out. I expect
that there are virtually no fossils from amoebae, ciliates and
flagellates, for they do not produce tests. Diatoms and foramins have
many fossil representatives. Many sponges have spicules that identify
them, Coelenterates like corals and gorgonians leave many fossils, but I
doubt that there are many from jellyfish. Some annelids produce siliceous
elements, but most helminths leave behind nothing but burrows--if they
burrow. I recall reading that, if every living thing except roundworms
were suddenly eliminated, their ghostly forms would remain in the
ubiquitous roundworms. Has anyone reported finding their traces in other
fossils that presumably would have harbored the tiny rascals? We've got
lots of molluscs fossilized (acres of clams), but I doubt that many of
these are octopods. I believe that there are relatively few invertebrate
sequences because there are few that readily fossilize, not because they
never existed. Can somebody familiar with the range of fossils confirm my
logic or tell me I'm all wet?

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Received on Thu Dec 7 14:20:45 2006

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