The Ichthyosauromorpha are an extinct

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

marine reptile Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. The earliest marine reptile mesosaurus (not to be confused with mosasaurus), arose in the Permian period during the ...

s consisting of the Ichthyosauriformes and the Hupehsuchia, living during the Mesozoic. The

node clade In general, a node is a localized swelling (a "knot") or a point of intersection (a Vertex (graph theory), vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two ...

Ichthyosauromorpha was first defined by Ryosuke Motani ''et al.'' in 2014 as the group consisting of the last common ancestor of ''

Ichthyosaurus communis ''Ichthyosaurus'' (derived from Greek ' () meaning 'fish' and ' () meaning 'lizard') is a genus of ichthyosaurs from the Early Jurassic (Hettangian - Pliensbachian), with possible Late Triassic record, from Europe (Belgium, England, Germany, Swi ...

'' and '' Hupehsuchus nanchangensis'', and all its descendants. Their

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

, unique derived traits, include: the presence of an anterior flange on the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

and radius; the lower end of the ulna being as wide as or wider than the upper end, the forelimb being as long as or longer than the hindlimb, the hand having at least three quarters of the length of the upper arm and lower arm combined, the fibula extending behind the level of the thighbone, and the transverse process of the vertebral neural arch being reduced or absent. The Ichthyosauromorpha probably originated in China during the upper Lower Triassic period, about 248 million years ago. One branch consisted of the Hupehsuchia, and the other of the Ichthyosauriformes, of which '' Cartorhynchus'' was a basal member. Other ichthyosauriforms were the Ichthyopterygia, containing the Ichthyosauria and allies. The last ichthyosaurs probably became extinct in the middle Cretaceous. Their relationships with other reptiles are unresolved, due to their highly derived morphology, even in their earliest known representatives, though they are usually considered to be diapsids.

Taxonomy

* Clade Ichthyosauromorpha ** Order Hupehsuchia ** Clade Ichthyosauriformes *** Clade Nasorostra *** Superorder Ichthyopterygia

Phylogeny

The internal phylogenetic structure of the Ichthyosauromorpha is shown by this cladogram:

References

{{Taxonbar, from=Q18534275 Olenekian first appearances Turonian extinctions