for Fish Fossils
Subclass Pteraspidomorphi (early jawless fish)
(unranked) Cephalaspidomorphi (early jawless fish)
Class Osteostraci (bony armored jawless fish)
Infraphylum Gnathostomata (jawed vertebrates)
Class Placodermi (extinct)
Class Chondrichthyes (cartilaginous fish)
Class Acanthodii (spiny sharks. extinct)
Superclass Osteichthyes (bony fish)
Class Actinopterygii (ray-finned fish)
Class Sarcopterygii (lobe-finned fish)
Subclass Coelacanthimorpha (coelacanths)
Subclass Dipnoi (lungfish)
comprise a paraphyletic group (containing taxa that
are descended from a common ancestor, but not including all
taxa descended from the common ancestor), including hagfishes,
lampreys, sharks and rays, ray-finned fishes, coelacanths,
and lungfishes. More formally, fishes are any non-tetrapod
chordates. One widely accepted taxonomy is shown to the right,
and some brief descriptions are given below for major groups
from which fossils are known.
The Agnatha are
the jawless fish, and the extant varieties are the last survivors
of the world's first vertebrate animals. Jawless fishes
diverged from other fish during the Cambrian some 500 million
years ago, and lack scales, paired fins, and jaws. They instead
have a circular toothed outgrowth used to latch on to the
side of another fish in order to feed on its blood.
Agnatha were prominent among primitive fishes of the early
Paleozoic. Haikouichthys and Myllokunmingia are notable agnathans
from the Chengjiang biota of China. Another putative agnathid
from Chengjiang is Haikouella. The Agnatha larvae are filter
feeders, a characteristic that betrays their evolutionary
kinship with invertebrate chordates. Many Ordovician, Silurian,
and Devonian agnathans were heavily armored with bony, spiked
plates. The Ostracoderms were the first armored agnathans,
ancesctors of the bony fishes and thus to tetrapods, including
humans, beings) that are are known from the middle Ordovician.
Agnathans never recovered from a decline during the Devonian.
The Chondrichthyes are
the cartilaginous fish having flexible skeleton of cartilage
rather than bone. They evolved some 100 million years after
the jawless fishes and the sharks, skates, and rays. They
have jaws, teeth and scales, and are, in general, effective
The teeth of carnivorous sharks are not attached to the jaw,
but instead are embedded in the flesh. Shark teeth of many
species are constantly replaced and some sharks can lose
30,000 teeth over their lifetime, which is why shark teeth
fossils are so abundant. In contrast, cartilagage poorly
fossilizes, making the cartilaginous fish fossils relatively
The Osteichthyes are
the bony fishes that evolved in conjunction with the cartilaginous
fish that are by far the largest group of fishes, have paired
fins, dermal scales, numerous vertebrae, and often many teeth.
The bony fish (Osteichthyes) can, in turn, be divided into
two categories, the lobe-finned fish and the ray-finned fishes.
Lobe-finned fishes have muscular fins supported by bones.
The lone surviving lobe-finned fishes is the coelacanth.
believes that terrestrial animals evolved from lobe-finned,
rather than ray-finned fishes. Ray-finned fish comprise all
other fish with a flexible skeleton made of bone. Osteichthyes
are the largest group of vertebrates comprising some 29,000