[Taxacom] What were Opabiniids?

[Kenneth Kinman]

 Hi all,
      The relationship between anomalocarids and opabiniids was first brought up by Bergstrom in 1986 and 1987 (Lethaia 19:241-246, and Lethaia 20:187-188).  The second paper was in response to a paper by Whittington, who just couldn't believe that they were closely related.  I would highly recommend that people read Bergstrom's papers.                  I followed Bergstrom's lead, and formalized this relationship in my 1994 classification (as Class Anomalocarea), but that classification covered ALL organisms, so it had no details on the evidence linking them.   Ben Waggoner's 1996 paper (Systematic Biology, 45:190-222) united anomalocarids, Opabinia, plus the Precambrian form Bomakellia, into a new clade "Anomalopoda".  Therefore I would not be surprised to see Order Bomakelliida someday transferred from Class Sprigginea into Class Anomalocarea.          In any case, although increasing numbers of workers have recognized the close relationship between anomalocarids and opabiniids, my hypothesis that opabiniids might just be a dwarf male or larval form of anomalocarids (with which they lived) has been widely ignored.  But just because Opabinia grew to be about 3 inches inlength, that does not mean it was necessarily an adult.  That proboscis could easily divide in two during metamorphosis (as well as a reduction in eye number and other changes).  But whether it is a larval form or dwarf male, who knows?  Hopefully someone will figure it out.                      ------ Ken Kinman