Fish Biology and Behaviour
Origins of Fish
Fish first fossil records of fish are of the Upper Cambrian Period in which fossils of Pikaia which was over 550 million years ago. Although it was worm like the it showed alot of characteristics of the order Cordata. Fish Started to dominate the sea in the Silurian and the Devonian periods. Where fish started to divesify and these were mostly carteligious in the Silurian Period and the first boney fish appeared in the the late Silurian Period. The devonian period is also know as The Age of Fishes. Towards the end of the Devonian the first tetrapods (vertebrates which evolved true legs with which they could walk on land) had evolved from one specific branch of fish. Fish greatly specialized in their aquatic niche during both the Devonian and the Silurian and part of this evolution led to adaptations to land in the form of amphibians.
A typical Silurian (Wenlock-Ludlow) vertebrate fauna from Saaremaa Island, Estonia. This fauna is dominated by agnaths, including thelodonts (1, Phlebolepis), heterostracans (2, Toypelepis), anaspids (3, Rhyncholepis), and osteostracans (4, Procephalaspis; 5, Witaaspis; 6, Thyestes; 7, Dartmuthia; 8, Tremataspis; 9, Oeselaspis). Jawed fishes are also present, especially acanthodians (10. Nostolepis) and possibly the earliest known osteichthyans (11. Andeolepis, known only from isolated scales and teeth). All these fishes lived in a marine environment, but osteostracans were more confined to lagoonal, shallow-water facies, whereas acanthodians and the lodonts were probably epipelagic.
early Devonian fish
Early Devonian fishes from the Old Red Sandstone of Spitzbergen (Wood Ray Formation). This fauna displays a remarkable number of jawed fishes, such as placoderms (1. Dicksonosteus, 2 Sigaspis), acanthodians (3. Mesacanthus), and porolepiformes (4. Porolepis). Jawless fishes nevertheless remain fairly abundant and diverse, with the same major taxa as in the Silurian, i.e. heterostracans (5. Zascinaspis 6. Doryaspis), osteostracans (7. Norselaspis, 8, Gustavaspis; 9, Belonaspis; 10 Boreaspis; 11. Parameterororaspis 12 Machiaraspis) and thelodonts (13 Turinia). As a whole, this fauna differs from the previous Silurian ones by the large size of some species (1, 4, 11) which could reach about a metre in length. These fish inhabited marginal marine (bay, estuarine, delta, etc) environments
Middle Devonian Fish
Fishes of the Middle Devonian locality of Lethen Bar, in Scotland (Givetian, about 377 Ma). They include antiarchs (1 Pterichthyodes); and arthrodire (2. Coccosteus) placoderms, acanthodians (3. Diplacanthus), ray-finned fish (4, Cheirolepis), lungfish (5, Dipterus), and osteolepiform lobe-finned fish (6. Osteolepis), representing the lineage that gave rise to land animals.
Late Devonian Fish
The marine fish fauna (found in association with coral reefs) from the famous Late Devonian locality of Gogo, north-western Australia (Early Frasnian), displays an amazing diversity of placoderms. Most of these are arthrodires (1, Eastmanosteus; 2, Latocamurus; 3. Tubonasus; 4, Incisoscutum; 5. Harrytoombsia; 6, Torosteus). Other placoderm groups are represented by the antiarch (7, Bothriolepis) and ptyctodontids (8, Campbellodus). The lobe-finned fishes are lungfishes (9, Holodipterus; 10, Griphognathus) and Osteolepiformes (11, Gogonasas). Small ray-finned fishes (12, Mimia) were also fairly abundant.
Esturine Late Devonian Fish
The Miguasha fish fauna (Escumenic fish fauna of Quebec (north central Euramerica) presents a remarkable diversity of early vertebrates, although chondrichthyans (sharks), which are largely represented in other localities of similar age, are absent. There is a variety of lobe finned fishes (sarcopterygia), belonging to five major taxa: the actinistians (1. Miguashuia). porolepiforms (2, Holoptychius), lungfishes (3, Scuamenacia), Osteolepiformes (4, Eusthenopteron), and elpistostegalians (5, Elpistostege), which are the immediate ancestors of the tetrapods. Ray-finned fishes (Actinopterygii) are rare with only one large form (6 Cheirolepis). In addition, there are archaic elements, such as the antiarch (7, Bothriolepis) and arthrodire (Plourdosteus) placoderms as well as acanthodians (9, Diplacanthus). and the youngest known osteostracan jawless fishes (10, Escuminaspis) Two anaspid-like naked jawless fishes (11. Endeiolepis, 12. Euphanerops) may be close relatives of the extant lampreys. These fishes lived in an estuary surrounded by ferns.
Eary Permium Fish
Early Permian fishes from the Copacabana Formation of Bolivia. The fauna still includes some of the peculiar chondrichthyans of the Carboniferous, such as huge engeneodontids (1. Parahelicoprion) and petalodontids (2, Megactenopetalus) along with primitive sharks (3) and a variety of ray-finned fishes (4, platysomids).
In the Early Permian, the last refuge for some of the vertebrate taxa that were widespread in Devonian times was the marginal, possibly brackish or freshwater, environment. exemplified here by the red beds of the Wichita Group of Texas. In this environment survived the youngest osteolepiform (1. Ectosteorhachis) and acanthodians (2. Acanthodes) in association with xenacanthiform (3) and hybodontiform sharks (4). as well as with coelacanths, lungfishes (5), and various ray-finned fishes (6). Various tetrapods (stem tetrapods and early synapsids, 7) also occur together with this fish fauna.