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I wonder where around the Los Angeles Basin these fossils were found? I suppose I'll have to inquire at the source. I've always been amused by the folks who think seismic activity will cause California to "fall into the ocean" when actually, millions of years of seismic activity seems to be having the opposite effect.
I don't think there are any argonaut fossils known from earlier than 40m years old. It's interesting to try to imagine how the earliest argonauts could have developed that primitive egg case. Perhaps a number of ancient octopods produced small egg cases, the argonauts taking the form to an extreme? Who knows? The fossil record of octopus is absolutely appalling, so it's fun to speculate.
Here's a fantastic introduction to argonauts from the Tree of Life pages: