Callovian genus first appearances

Equisetum (; horsetail) is the only living genus in Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.

Ophthalmosaurus (Greek ὀφθάλμος ophthalmos 'eye' and σαῦρος sauros 'lizard') is a genus of ichthyosaur known from the Middle-Late Jurassic. Possible remains from the earliest Cretaceous (Berriasian stage) are also known. It was a relatively medium-sized ichthyosaur, measuring long and weighing . Named for its extremely large eyes, it had a jaw containing many small but robust teeth. Major fossil finds of this genus have been recorded in Europe with a second species possibly being found in North America.

Leedsichthys is an extinct genus of pachycormid fish that lived in the oceans of the Middle to Late Jurassic. It was the largest ray-finned fish, and amongst the largest fish known to have ever existed.

Isanichthys is an extinct genus of freshwater lepidotid ginglymodian fish from the Late Jurassic and Early Cretaceous. Four species are known from Thailand, China and the United Kingdom, two of which were previously classified in genera.