Today’s most successful fish weren’t always evolutionary standouts

Take a glance around the oceans, rivers and lakes of today and you’ll confront an astonishing diversity of fish, from narrow-bodied eels to the 25-foot-long giant oarfish to delicate, fluttering seahorses. The vast majority of fish alive today — approximately 96 percent — are known as teleosts, a group of ray-finned fish that emerged 260 million years ago.