Pycnodontiformes

Pycnodontiformes Temporal range: Late Triassic–Eocene PreꞒ Ꞓ O S D C P T J K Pg N
Pycnodontiform diversity
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Subclass:	Neopterygii
Order:	†Pycnodontiformes Berg, 1937
Families
Brembodontidae Coccodontidae Gebrayelichthyidae Gladiopycnodontidae Gyrodontidae Hadrodontidae Mesturidae Pycnodontidae

Pycnodontiformes is an extinct order of primarily marine bony fish. The group first appeared during the Late Triassic and disappeared during the Eocene. The group has been found in rock formations in Africa, Asia, Europe, North and South America.^[1]

They were small to middle-sized fish, generally with laterally-compressed deep bodies, some with almost circular outlines,^[2] adapted for manuverability in reef-like environments, though the group was morphologically diverse.^[3] Most, but not all members of the groups had jaws with round and flattened teeth,^[4] well adapted to crush food items (durophagy), such as echinoderms, crustaceans and molluscs.^[3] Some pyncodontiformes developed piranha like teeth used for eating flesh.^[5][6] Most species inhabited shallow marine reef environments, while a handful of species lived in freshwater or brackish conditions.

While rare during the Triassic and Early-Middle Jurassic, Pycnodontiformes became abundant and diverse during the Late Jurassic, exhibiting a high but relatively static diversity during the Early Cretaceous. At the beginning of the Late Cretaceous they reached their apex of morphological and species diversity (much of this due to fossils found in the Sannine Formation of Lebanon, such as Gebrayelichthyidae and Ichthyoceros), after which they began to gradually decline, with a more sudden decline at the end of the Cretaceous due to the collapse of reef ecosystems, finally becoming extinct during the Eocene. They are considered to belong to the Neopterygii, but their relationship to other members of that group is uncertain.^[3]