Osteolepis macrolepidotus Devonian Fossil Fish

An Ancient Lobe-Finned Ancestor of Tetrapods from Scotland

Osteolepis macrolepidotus

Class Sarcopterygii, Infraclass Tetrapodomorpha, Superorder Osteolepidida, Order Osteolepiformes, Family Osteolepidae

Geological Time: Middle Devonian

Size: 175 mm in length

Fossil Site: Cruday Quarry, Orkney, Scotland

Fossil Fish Osteolepis macrolepidotuDescription: Osteolepis is a member of Order Osteolepiformes within Vertebrata Class Sarcopterygii, the so-called lobe-finned fish. While they are bony fish, they are formally considered in classical cladistics to be terrestrial vertebrates and are among the many ancestors of tetrapods that conquered the land late in the Devonian Period (~ 360 million years ago). Osteolepis is noted for Osteolepis Paleoarthaving scales and plates on its head that were covered with a thin layer of cosmine scales (a spongy but bony material).

Osteolepiformes is also included in an unranked (but believed monophyletic) clade Rhipidistia made up of Tetrapoda and still extant lungfishes and Coelacanths. Traits that place Osteolepis within the lobe-finned fish are paired lobed fins and posterior nasal passages called choanae between the nasal cavity and the throat in tetrapods, including humans, that allow breathing when the mouth is closed. Osteolepis is also noted for think rhombic-shaped as seem in the fossil images here. These Devonian fish had many characteristics that would be largely retained when the first fish walked ashore.

 Tetrapod Ancestor Fossil Fish
Images by permission from Fossil Mall (CC BY-NC 4.0)

Also see: Sarcopterygii Fish Fossils Osteolepis panderi

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