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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 I'm not sure how similar the gills are, but I'll bet unpublished observations on these and many other characteristics would support my views.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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