Many new groups of organisms evolved in a relatively short time in an event called the

It is called the cambrian explosion. It is where new groups of organisms arises and are being classified and it is during the period of the cambrian, one of the reason why it was named after it. It has the highest animals found during that time and it could be found on the fossil records that has been established.

That is true! many fish species traveled to the u.s. because of it.