Ichthyodectiformes


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.
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.
Most ichthyodectiforms ranged between 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. There is evidence that at least one species, Xiphactinus audax, may have been endothermic. Another genus, Dugaldia, may have been able to laterally open its mouth extremely wide in a manner akin to the modern sarcastic fringehead.

Systematics

The basal phylogeny is badly resolved, leading to many ichthyodectiforms that are simply known to be rather primitive, but where nothing certain can be said about their precise relationships.
IchthyodectiformesAfricathrissops Taverne, 2010Allothrissops Nybelin, 1964Antarctithrissops Arratia et al., 2004Ascalabothrissops? Arratia, 2000Capassoichthys Taverne, 2015Carsothrissops d'Erasmo, 1946Dugaldia Lees, 1990Faugichthys Taverne & Chanet, 2000Furloichthys Taverne & Capasso, 2018Occithrissops Schaeffer & Patterson, 1984Ogunichthys Alvarado-Ortega & Brito, 2009Pachythrissops? Woodward, 1919Prymnetes Cope, 1871Thrissops Agassiz, 1843Sultanuvaisia Nesov, 1981Unamichthys Alvarado-Ortega, 2004Verraesichthys Taverne, 2010Chuhsiungichthyidae? Yabumoto, 1994