The second major ichthyosaur extinction took place during the Cenomanian-Turonian boundary event, an 'anoxic event', eliminating the apex predators, after which just a single lineage survived, Platypterygius hercynicus, which disappeared shortly afterwards, about 93 million years ago. Ichthyosaur extinction was thus a pair of abrupt events rather than a long decline, probably related to the environmental upheavals and climatic changes in the Cenomanian and Turonian. If so, it was not caused by mosasaurid competition; large mosasaurs did not appear until 3 million years after the ichthyosaur extinction, likely to fill the resulting ecological void. Plesiosaurian polycoltylids perhaps also filled some of the niches previously occupied by ichthyosaurs, although they had coexisted for 19 million years. The extinction was most likely the result of ecological change and volatility that caused changes in migration, food availability, and birthing grounds. This part of the Cretaceous was one in which many other marine extinctions occurred, including those of some types of microplankton, ammonites, belemnites, and reef-building bivalves. Taxonomy This taxonomy was presented by Michael Werner Maisch in his 2010 review of ichthyosaur classification. Clade Ichthyopterygia (sensu Motani (1999)) Genus Chaohusaurus Family Grippiidae Family Parvinatatoridae Family Thaisauridae Family Utatsusauridae ? Family Omphalosauridae ? Genus Isfjordosaurus Order Ichthyosauria (sensu Motani (1999)) Family Quasianosteosauridae Parvorder Hueneosauria Nanorder Mixosauria Family Wimaniidae Family Mixosauridae Nanorder Longipinnati Family Toretocnemidae Family Cymbospondylidae Hyporder Merriamosauria Family Merriamosauridae Family Besanosauridae Family Shastasauridae Family Shonisauridae Family Californosauridae Minorder Parvipelvia Family Hudsonelpidiidae Family Macgowaniidae Suborder Neoichthyosauria Family Temnodontosauridae Family Leptonectidae Family Suevoleviathanidae Infraorder Thunnosauria Family Ichthyosauridae Family Stenopterygiidae Family Ophthalmosauridae Phylogeny In modern phylogeny, clades are defined that contain all species forming a certain branch of the evolutionary tree. This also allows one to clearly indicate all relationships between the several subgroups in a cladogram. In 1999, a node clade Ichthyopterygia was defined by Motani as the group consisting of the last common ancestor of Ichthyosaurus communis, Utatsusaurus hataii and Parvinatator wapitiensis; and all its descendants. Within Motani's phylogeny, the Ichthyopterygia were the larger parent clade of a smaller stem clade Ichthyosauria that was defined as the group consisting of Ichthyosaurus communis and all species more closely related to Ichthyosaurus than to Grippia longirostris. Motani's concept of the Ichthyosauria was thus more limited than the traditional one that also contained basal forms, such as Grippia, Utatsusaurus, and Parvinatator. The following cladogram is based on Motani (1999): An alternative terminology was proposed by Maisch & Matzke