Cheirolepis

Cheirolepis (from χείρ kheír, 'hand' and λεπίς lepis 'scale') is an extinct genus of marine and freshwater ray-finned fish that lived in the Devonian period of Europe and North America. It is the only genus yet known within the family Cheirolepididae and the order Cheirolepidiformes. It was among the most basal of the Devonian actinopterygians and is considered the first to possess the "standard" dermal cranial bones seen in later actinopterygians.

Cheirolepis was a predatory freshwater and estuarine animal about 55 cm long. It had a streamlined body with small, triangular ganoid scales similar to those of the Acanthodii. These scales had a basic structure typical of many early osteichthyans, with a superficial of ganoine overlying dentine, and a basal plate of bone. Cheirolepis had well-developed fins which gave it speed and stability, and was probably an active predator. Based on the size of its eyes, it hunted by sight. Cheirolepis's jaws, lined with sharp teeth, could be opened very wide, allowing it to swallow prey two thirds of its own size.

Species
The following species are known:


 * C. aleshkai Plax, 2020 - Middle Devonian (Eifelian) of Belarus
 * C. bychovensis Plax, 2022 - Middle Devonian (Emsian & Eifelian) of Belarus
 * C. canadensis Whiteaves, 1881 - Late Devonian (Frasnian) of Miguasha, Canada
 * C. gaugeri Gross, 1973 - Middle Devonian (Givetian) of Belarus & Estonia
 * C. gracilis Gross, 1973 - Emsian & Eifelian of Belarus & Estonia
 * C. jonesi Newman, Burrow, den Blaauwen & Giles, 2021 - Givetian of Spitsbergen, Svalbard
 * C. trailli Agassiz, 1835 (type species) - Middle Devonian (Eifelian & Givetian) of Scotland
 * C. schultzei Arratia & Cloutier, 2004 - Middle Devonian (Givetian) of Nevada, USA

C. schultzei is known from Red Hill, Nevada deposited during the Mid-Late Devonian boundary. The specimen from which this species was named, consisting of scales and a lower jaw, was originally referred to C. canadensis. Many species, including C. aleshkai,C. bychovensis, C. gracilis & C. gaugeri are only known from isolated scales.

The species C. sinualis from Belarus is considered a nomen nudum. The species C. cummingae Agassiz, 1845, C. macrocephalus M'Coy 1848 , & C. uragus Agassiz, 1835 are considered conspecific with C. trailli