Life tries again
After the extinctions at the end of the Cambrian, the Ordovician once again came with a sudden increase in the amount and variety of life. This time, those who survived the end of the Cambrian would diversify, so life didn’t quite start over. This period saw the armored jawless fish, and just before it’s end, some fish with jaws, which is as far as vertebrates got so far. There were also giant relatives of octopus and squid, with shells that got anywhere from 20 to 40 feet long, and the very first land plants make their appearance.
Here’s the first fishy link.
Here’s the second fishy link, about the early evolution of vertebrates, early vertebrates AKA. Fish.
Here are a couple of articles with general information about the Ordovician.