The Ichthyosauromorpha are an extinct clade of marine reptiles consisting of the Ichthyosauriformes and the Hupehsuchia, living during the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

. The node clade Ichthyosauromorpha was first defined by Ryosuke Motani ''et al.'' in 2014 as the group consisting of the

last common ancestor In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...

of '' Ichthyosaurus communis'' and '' Hupehsuchus nanchangensis'', and all its descendants. Their synapomorphies, unique derived traits, include: the presence of an anterior flange on the humerus and

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

; the lower end of the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

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 The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity i ...

extending behind the level of the thighbone, and the transverse process of the vertebral

neural arch The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

being reduced or absent. The Ichthyosauromorpha probably originated in China during the upper

Lower Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is a un ...

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 Ichthyopterygia ("fish flippers") was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic ichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitiv ...

, containing the

Ichthyosauria Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...

and allies. The last ichthyosaurs probably became extinct in the middle

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

. 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 Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ag ...

Taxonomy

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

Phylogeny

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

References

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