I don't think it is a fossil lamprey
kinman at HOTMAIL.COM
Sat Sep 25 22:31:07 CDT 1999
Whatever it is, I would say that it is far more primitive and
generalized than either anomalocarids or lampreys. But the fact that there
are no apparent arthropod characteristics does not exclude it from being an
arthropod. Cirripeds (barnacles) certainly don't look like arthropods until
you look at the developmental stages. And other adult forms are rather
deceptive (pentastomids don't look much like arthropods, much less
crustaceans, but that's what they are).
My experience from problematic fossils is that you have to look at the
obvious candidates first, and try to rule out convergence when you can. But
you always have to look out for the unexpected. Quite frankly, we have to
remember these are fossils, and we only have a few (not very good) examples.
If we can't even figure out where to put enigmatic living groups (like
cycliophorans), it could be a long time before we have a good idea where
these fossils belong. Chancellorid fossils have been around a century, and
we still don't have any really solid ideas what they are. It's fun to
speculate, but the speculation on a form like Xidazoon has only just begun,
and having only seen the article once, my speculations aren't probably worth
much at this point.
I doubt that they belong to Class Priapulea, since Simon Conway Morris
(one of the authors of the article) is the world's authority on fossil
priapulids. But I still wouldn't be surprised if they were something
evolutionary intermediate between priapulids and anomalocarids. The
radiation of metazoan phyla occurred in the Precambrian, not the so-called
Cambrian explosion (which is more apparent than real, being merely an
explosion of "hard parts" which show up disportionally in the fossil
record). In fact, virtually all metazoan phyla were probably present during
the transition from Precambrian to Early Cambrian.
Therefore, these fossils could belong to any one of many different
groups, even among primitive deuterostome invertebrates or the
lophophorates. But my initial impression still remains among Phylum
Protarthropoda or early Arthropoda. Perhaps a more careful study of the
article will narrow the possibilities in my mind. But some relationship
with an "aschelminth" group wouldn't surprise me, and it is interesting to
note that some aschelminth authorities believe anomalacarids may be as
closely related to some "aschelminths" as they are to arthropods.
>From: Geoff Read <g.read at NIWA.CRI.NZ>
>Reply-To: Geoff Read <g.read at NIWA.CRI.NZ>
>To: TAXACOM at USOBI.ORG
>Subject: Re: I don't think it is a fossil lamprey
>Date: Sat, 25 Sep 1999 10:20:49 +1200
>In response to J Bruner's post K. Kinman ranged the field including:
> > I immediately thought of Class Anomalocarea
> > (Phylum Arthropoda).
>Interesting. What arthropod characters do you see in that sac-like body?
>It must be the 'mouth' then. But it is too poorly delineated to be made a
>convincing Anomalocaris-type mouth - or that of a fossil lamprey.
>Geoff Read <g.read at niwa.cri.nz>
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