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Temporal range: Early Devonian, 421–409 Ma
Ischnacanthus gracilis life restoration.jpg
Life restoration of Ischnacanthus gracilis
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Acanthodii
Order: Ischnacanthiformes
Family: Isnacanthidae
Genus: Ischnacanthus
Type species
I. gracilis
Egerton, 1861

Ischnacanthus is an extinct genus of jawed fish in the class Acanthodii. It lived during the Early Devonian period, approximately 421–409 million years ago. It is known from a single species, which is also the type species, I. gracilis.

Discovery and naming[edit]

Primitive acanthodians, Mesacanthus pusillus, Parexus falcatus, and Ischnacanthus gracilis

Ischnacanthus was first discovered in 1861 by Egerton, and later assigned to Isnacanthidae by A. S. Woodward in 1891.[1] The type specimen that defines this species is named Ischnacanthus gracilis, and helps outline the Isnacanthidae family it belongs to. Fossils of this fish were first discovered in Tillywhandland Quarry, Forfar, Scotland.[2] The Acanthodians, the class Ischnacanthus is home to, are the subject of some dispute over their systematic position because they have features of both bony fish, the Osteichthyes, and cartilaginous fish, the Chondrichthyes.[2]


Ischnacanthus was a fish in the class Acanthodii that had a long body covered in mosaic-like scales, and likely grew up to 2 m in length.[3] They possess highly advanced, spindle-shaped bodies that were thought to have made them swift swimmers. This fish had two narrow dorsal spines, one either side of and just behind its head.[2] It was a predatory fish that possessed a mouth with very small teeth on the lower jaw. The feature all Acanthodians share in common is the fact that massive spines, formed of dentine, support all fins other than the caudal fins.[2] This species probably lived in Lake Forfar, which is a fresh-water lake surrounded by volcanoes.


  1. ^ Woodward, A. S. "Catalogue of the Fossil Fishes in the British Museum". Catalogue of the Fossil Fishes in the British Museum (2). 
  2. ^ a b c d "Complete Acanthodian Fossil Fish From The Devonian Of Scotland". FossilMall. Retrieved November 7, 2017. 
  3. ^ "Teleostomi, Acanthodians". Palaeos. Retrieved November 7, 2017.