Sexual dimorphism

The Jurassic ammonites Stephanoceras and the smaller genus Mollistephanus each come in two size ranges, the females (macroconches) being many times larger than their male counterparts (microconches). A female Mollistephanus is similar in size to a male Stephanoceras, which is a challenge to people like Bob Chandler who is investigating the zonal spreads and evolution of Middle Jurassic ammonites. Intriguingly, evidence has been found that they can sometimes change sex. A Stephanoceras male, feeling unfairly treated by evolution, decides to take drastic action. . .


Sexual equality? No chance of that round here!
My missus is a macroconch, and likes to make it clear
That we’re sexually dimorphic – she’s in charge, and I’m in fear.
Well, I might be ten times smaller, but I’ve had a great idea.

I’ll tell you what I’ll do, although you’ll think I’m off my trolley:
I’ll change my sex, and change my name; not Stephan now, but Molli.
My ammonitic friends will reckon I’m a dishy dolly;
But for Molli males a tenth my size, to cross me would be folly!

In times to come geologists will hammer at the ground,
Then out I’ll pop. Bob Chandler and his buddies will assemble all around.
“A Stephan micrconch? A macro Molli? No. We’ve found
A hen-pecked, sex-changed, chimera – the only one around!”

[Photos: ammonites.fr (stephanoceras, left); ammonites.fr (mollistephanus, right)
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