Ichthyodectiformes

Ichthyodectiformes Temporal range: Middle Jurassic-Early Paleocene PreꞒ Ꞓ O S D C P T J K Pg N
Xiphactinus audax Ichthyodectes ctenodon Cladocyclus gardneri Chirocentrites sp.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Division:	Teleostei
Order:	†Ichthyodectiformes Bardack & Sprinkle, 1969
Subgroups
See text

Ichthyodectiformes is an extinct order of marine stem-teleost ray-finned fish. The order is named after the genus Ichthyodectes, established by Edward Drinker Cope in 1870. Ichthyodectiforms are usually considered to be some of the closest relatives of the teleost crown group.^[1]

They were most diverse throughout the Cretaceous period, though basal forms like Thrissops, Occithrissops and Allothrissops are known from the Middle-Late Jurassic of Europe and North America. They were almost entirely wiped out by the Cretaceous-Paleogene extinction event, but a single species, Saurocephalus lanciformis, appears to have survived into the earliest Paleocene (Danian).^[2]

Most ichthyodectiforms ranged between 1 and 5 meters (3–15 ft) in length. Most of known taxa were predators, feeding on smaller fish; in several cases, larger ichthyodectiforms preyed on smaller members of the order. Some species had remarkably large teeth, though others, such as Gillicus arcuatus, had small ones and sucked in their prey. Heckelichthys preopercularis is a rare example of non-predatory ichthyodectiform, more likely to be microphagous, fed on small particles.^[3] There is evidence that at least one species, Xiphactinus audax, may have been endothermic ("warm-blooded").^[4] Another genus, Dugaldia, may have been able to laterally open its mouth extremely wide in a manner akin to the modern sarcastic fringehead.^[5]