Jurassic Park Period Part 5

Fauna - Fish

I don't have as much information on the fish of the Jurassic as I had on the reptiles. So this blog might not be as long. But we'll see.

Conodonts - This is a class of jawless fish that had hard tooth-like elements. They were mentioned in the article I consulted only because they died out during the Jurassic, although not all over the globe at the same time. They had over 300 million years of evolutionary history, but only a handful of species made it into the Jurassic, and those went extinct early in the period. So they wouldn't have been plentiful in the oceans, but there might have been some, depending on what time during the Jurassic period a person was looking.

Sarcopterygii - This is a fancy name for lobe-finned fish, a class of fish whose fins are attached to their bodies by a single bone. This includes several genera of lungfish, which lived in freshwater environments in both hemispheres. Some of those lungfish are fairly closely related to lungfish now living in South America and Africa, rather than those living in Queensland. And there were some living in Asia that are not closely related to any group of living lungfish. Another group of this type of fish were the Mawsoniids, which are completely extinct now, but which lived in the oceans or fresh or brackish water.

Bony fish (Actinopterygii) were major components of freshwater and marine ecosystems. Among these were the Amiiform fish, which are represented today only by the bowfin, an elongated, eel-like creature with sharp, pointy teeth that live in slow-moving fresh water. During the Jurassic, the Amiiformes became fairly global. The pycnodontiforms were small to middle-sized fish with laterally-compressed body and an almost circular outline. They lived mostly in shallow-water sea. They had round and flattened teeth, well adapted to crush food items. Some species lived in rivers and possibly fed on molluscs and crustaceans. Although they had a large variety of representatives during the Jurassic, they are all extinct now. Teleosts, which currently make up over 99% of living Actinopterygii, appeared during the Triassic and underwent a major diversification during the Late Jurassic. The Pachycormiformes are a group of fish closely allied to teleosts. They first appeared in the Early Jurassic, and included both tuna-like predatory and filter-feeding forms. This included the largest bony fish known to have existed, with an estimated maximum length over 15 metres (45 feet).

Chondrichthyes - are fish whose skeletons are mostly made of cartilage, rather than bone. During the Early Jurassic, Hubodonts, which appear to have been primitive forms of sharks were common in both marine and freshwater settings. However, by the Late Jurassic, hybodonts were minor components of most marine communities, having been largely replaced by neoselachians, which contains all living sharks and rays. Hybodonts remained common in freshwater and restricted marine environments. Relatives of the bullhead shark, carpetsharks, and mackerel sharks all made their appearance during the Jurassic. There were also other examples of extinct and relatives of now-living sharks mentioned, so I would suppose that shark-like creatures were a regular feature in the oceans.

So there were plenty of fish in the seas.

https://en.wikipedia.org/wiki/Jurassic