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Opabinia & "Dino-carids"
Answering some misconceptions I've received,
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), and
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the gills are, but I'll bet unpublished observations on these and many other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. I know----wait for the papers!!!,
but some have been in limbo for nearly a decade. ARGH!!!! Frustration.
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).
It would seem that taxonomic inflation may be a problem for dinosaurs,
dinocarids, and perhaps paleontology in general. So it goes. Good night
all. TGIF tomorrow, I'm exhausted.
---Cheers, Ken Kinman
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