The Devonian Period was a golden age for life in the ocean, in fact it’s called the Age of Fishes. First the jawless fish evolved but soon swimming around in a fishy way seemed pretty sweet and everyone was doing it. Fish with jaws emerged and were hardcore with the eating of other fish, then ancient sharks hit the scene.
As life underwater was taking off, plants began to move to the land, perhaps they were sick of being lunch for fish. Green ferns were among the first to stake their leafy claim, but shortly after insects followed, and plants were right back to being lunch again.
There was lots of life, lots of diversity, lots of new things and lots of feasting to be had. But the party had to end eventually, and indeed the last 20 million years of the Devonian were part of a long, drawn out mass extinction.
The extinction at the end of the Devonian was massive, it’s in the “five major extinction events” along with our favourite dinosaur-ending Cretaceous episode. Nearly 70% of all invertebrates would never be seen again, and the marine world was the worst hit.
Why did this massive extinction happen?
Your guess is as good as mine, but there are theories about. One is that the plants stripped the carbon dioxide from the air, causing global cooling. Maybe an asteroid is to blame, which I blame the dinosaur extinction on myself. Or maybe they all got fish flu.
There’s some evidence in rocks which date back to that time that the waters were very low in oxygen at the time of the extinction, so perhaps that was involved. It’s probably a mixture of events that by themselves would have been okay, but add them together and not much can survive. Excluding this familiar character which has done a damn good job of surviving.
It was at the end of the Devonian that the lungfish evolved and made it’s way onto land, beginning an air-breathing trend that I am proud to continue.
Up until now people believed the lungfish grew up in freshwater, because there’s still some freshwater lungfish around today. Looks like the textbooks will have to be rewritten now, because of this little guy.
Introducing a brand-new discovered-in-2008 lungfish Rhinodipterus that lived in SALTwater! Why does this matter? Well, it suggests that the ability to breathe air happened twice in the Devonian, once in freshwater and once in saltwater. The researchers suggest that one of these fish went on to evolve into other animals, while the other stayed back and remained a lungfish.
Their report will be published in this weeks edition of Biology Letters, which I’m sure all my readers will be DYING to read. But next time someone says “we evolved from lungfish” you can counter with “freshwater or salt?”
If you’d like to read more and don’t want to tackle the journal article, here’s the press release from the Australian National University. Hey, I study there. Maybe I should get an interview…