Opabinia = Anomalocaris (up to 80%)

[Ken Kinman]

Bill,
     Unfortunately, the myth that all Anomalocaris were large is perpetuated
in both the scientific and popular press, because of a preoccupation with
how big the biggest ones got.  The smallest Anomalocaris specimens are
apparently very small (about 3 inches long), the same size as the larger
Opabinia specimens.  A slight overlap in size supports my case for the
larval hypothesis.  See Chen, Ramskold, and Zhou, 1994 (Science, 264:
1304-1308) for pictures of small anomalocarids.
    And the median eye of Opabinia is most likely homologous to the median
eye of nauplius larvae in crustaceans.  If and why Opabinia has two pairs of
stalked eyes seems to be a mystery to everyone, but one can't rule out the
possibility that one pair is homologous to a pair of antennae.
     The segmentation in Anomalocarids and Opabinia is very similar, both
have biramous limbs (the upper branches modified into swimming flaps),
almost everyone notices the very similar tail fan.  I'm not sure how similar
the gills are, but I'll bet unpublished observations on these and many other
characteristics would support my views.
     In spite of the differences, Opabinia appears to be a very good match
for what one should expect from a larval Anomalocarid.  And it is beginning
to appear that wherever anomalocarids are found, so are Opabinia-like
animals.  The more I think about it, I believe 49% is too low a probability
for the larval hypothesis.  Maybe 60% for the larval hypothesis, 20% for the
dwarf male hypothesis, and 20% that they aren't variant forms of the same
animals (the traditional view).
     As for me being the odd man out, remember that Hallucigenia with
"stilt-legs" was widely accepted by scientists until someone finally looked
for evidence to falsify that notion.  Authorities make big mistakes too,
including a decade of disbelief that ulcers could possibly be caused by a
bacterium (which continued long after that doctor swallowed Helicobacterium
to prove his point).  That stress was the main cause of ulcers was obviously
very "believable" and espoused by thousands of authorities for decades, but
that didn't make it right.  To me the larval hypothesis of Opabinia makes a
heck of a lot more sense than a worm on stilt-legs.
                    Cheers,  Ken Kinman
*******************************************************
Bill wrote:
>Also as you state, Opabinia were very small and nearly all the Anomalacaris
>are from 0.5 to 1.0 meters long.  Where are the intermediate life history
>stages?
>
>Both Graham Budd and Simon Conway Morris think the two are closely related,
>but distinct, animals.  Both these guys as well as Whittington and Derek
>Briggs have studied the actual fossils and have a lot of experience in a
>wide range of arthropods.  What they have to say about the two animals is
>detailed and quite believable.
>
>So, since you are the odd man out, you have to prove your case.
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