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 "Thrissops" fossils are known from the Oxfordian-Kimmeridgian boundary in the Late Jurassic. Most ichthyodectiforms ranged between 1 and 5 meters (3–15 ft) in length. All 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. There is evidence that at least one species, "Xiphactinus audax", may have been endothermic ("warm-blooded"). 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. Ichthyodectiformes