Jawless Fish – (Lamprey and Hagfish)
Armored Fish – (Placoderm – Dunkleosteus)
Spiny Sharks – (Chondrichthyes – Cartilage Fish)
Lobe-finned – (Coelacanth-Living Fossil)
Ray-FinnedFish – (Actinopterygii – Modern Fish)
The study of fish is called Ichthyology. The study of prehistoric fish, their fossils and environment is called Paleo-ichthyology (“Study of Ancient Fish”). Fish were the first vertebrates to develop on Earth due to the earliest known vertebrates found in the fossil record. Primitive fish first appeared in the Cambrian Period approximately 510 Million years ago and developed, diversified and of course exist today with thousands of different species throughout the world in both fresh and salt water environments.
Ancient fish are classified in groups that describe major morphological differences. The earliest classifications are the Jawless Fish, Armored Fish, Spiny Sharks, Ray-FinnedFish, Boney Fish and the Lobe-finned fish like the Coelacanth. Many ancient species like the jawless fish, sharks, rays and even the Coelacanth still exists today. These living fossil and similar species can be found in the fossil record throughout the Paleozoic and are abundant throughout the Devonian.
The jawless fish, Agnathans (“without jaws”) like lampreys and hagfish alive today as well were the earliest and most primitive fish to develop. They had bony fins, thick scales and developed armor like bony scaling with bony spines representing fins. Their mouths were fixed open because they did not have jaws and would suck in food particles from the muddy bottom or surrounding water. The jawless fish developed in the sea but later invaded rivers and lakes.
During the Devonian Periodconsidered the“Age of the Fish”, The Placoderms(“Plated Skins”) or Armored Fishappeared during the end of the Silurian and the by the beginning of the Devonian Periods. This sea going predator is believed by scientists to be the closest relative of all living jawed fish. The Placoderms became extinct by the end of the Devonianor possibly the beginning of the Mississippian(Carboniferous) Period, about 365 million years ago.
Placoderms had large heads, powerful jaws, razor sharp teeth and an armored bony plated head. The most famous Placoderm fossil is Dunkleosteus (named after the founder Mr. Dunkle) and is the largest and most famous of the Placoderms found so far in the fossil record.It ranged in size from a few inches to 26 feet long and was a top predator in the seas.
About 420 million years ago the Chondrichthyes(“Cartilage Fishes”) appeared by the late Silurian Period in many of the seas around the world. This group includes sharks, rays and ratfish which have changed very little over time. Many species of shark like fish have evolved throughout time but still possess the basic features of a streamlined body, sharp teeth, speed and maneuverability and ferocious appetite. When discussing ancient sharks the one that comes to mind first is Megladon. Megladon (Giant Tooth) was an ancient shark probably related to our Great White Shark of today with a difference. The “Meg” measured about 50 feet in length and had 7 inch teeth and was the top predator of its time. A reconstruction of its jaws is on display at the Museum of Natural History in New York City. My recollection of its size is that you could drive a mid-sized into its jaws and still have some room on the sides.
By the late Silurian and early Devonian approximately 420 million years ago the modern boney fishes appeared, called the Osteichthyes. A subclass of the Osteichthyes is the ray-finned fishes, called the Actinopterygii. They and were and are the dominant group of fishes from approximately 420 million years ago to the present representing thousands of different species in both fresh and salt water around the world.