The origins of those sexual organs: a fishy tale much more primitive than we thought

July 19, 2018 by John Long And Marion Chevrinais, The Conversation

Euphanerops, a primitive jawless fish from the World Heritage site at Miguasha, Quebec, which has now been found to have paired hind limb structures and copulatory sex organs. Credit: François Miville-Deschênes with permission, Author provided

Fossil discoveries from the Devonian rocks of Scotland and Australia first revealed that the earliest jawed fishes, the placoderms, reproduced using copulation in much the same way as sharks and rays do today.

They also had the first paired pelvic skeletons, the precursor to the hind paired fins – and legs – of all animals. Their paired reproductive organs, called "claspers", probably developed in the same way as limbs.

The appearance of jaws and teeth in the first vertebrates was thus intimately linked to the origin of paired hind limbs (pelvic girdles) and an advanced kind of sexual reproduction.

Read more at: 

The First Vertebrate Sexual Organs Evolved as an Extra Pair of Legs

By John Long, Flinders University and Kate Trinajstic, Curtin University | June 10, 2014 

This article was originally published at The Conversation. The publication contributed the article to Live Science's Expert Voices: Op-Ed & Insights.

We humans use the euphemism for sex that “we like to get a leg over” but the first jawed vertebrates – the placoderms – they liked to get a leg in.

They were the first back-boned creatures to evolve male genital organs, or claspers, supported by a bony internal skeleton.

What’s even more peculiar is that, unlike the cartilaginous claspers of modern sharks, which are a modified part of the pelvic fin, our new research has shown that in placoderms they were basically a separate set of paired appendages.

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