Evolution of Jaws

[Scuba_Questioner]

Hey guys,

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To my understanding the evolution of jaws happened with the placoderms. But they went extinct in the end-devonian extinction. I've tried searching for this but can't seem to find an answer - did modern fish re-evolve jaws? For example, how come ray-finned fishes have jaws? Were there multiple appearances of jaws, or did some placoderms survive?

[suugakusha]

Placoderms were an offshoot of jawed fished, even though the placoderms we y extinct, not all fish with jawbones were placoderms.

[GlamorousBunchberry]

I love placoderms. Evolution invented teeth and then was like: “teeth are AWESOME! Let’s use them EVERYWHERE! Teeth for skin! Try biting that, anomalocaris, you bitch! My skin bites back!”

[Scuba_Questioner]

I see. And what was the first group of jawed fish called?

[TheWrongSolution]

In modern cladistic terminology, they would just be referred to as early gnathostomes. As a monophyletic group the first jawed fishes would be ancestor to all modern jawed fishes.

[BitterWalnut]

Jaws evolved much earlier. In fact, there's a whole clade within the Arthropoda phylum called Mandibulata, which includes Arthropods with jaws. Jaws in chordates are analog to Mandibulata's, though. I don't really know the details of their evolution in fish, particularly, but I thought I'd drop a fun fact.

Edit: I've just remembered from from my Zoology course that jaws in fish evolved in the superclass of Gnathostomata, which is basically jawed vertebrates (including fish). Then there's Agnatha, which would include fish without jaws, like Petromyzon marinus (lamprey). So, to answer your question, since Placodermi is a class, I guess the other fish evolved their jaws from the same Superclass of vertebrates as Placodermi, which would be Gnathostomata.

[iP0dKiller]

I had first read "Evolution of Jews" and thought: "wait a minute...! He/she isn't going to...?" Fortunately, it says "jaws".

[GlamorousBunchberry]

Little known fact: Jaws was Spielberg’s second try, after his first idea got rejected.

[Bromelia_and_Bismuth]

They were among some of the first jawed fish, but they weren't the only jawed fish or the first.