The Ichthyosauriformes are a group of marine

reptiles Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

, belonging to the

Ichthyosauromorpha The Ichthyosauromorpha are an extinct clade of Mesozoic marine reptiles consisting of the Ichthyosauriformes and the Hupehsuchia. The node clade Ichthyosauromorpha was first defined by Ryosuke Motani ''et al.'' in 2014 as the group consisting ...

, that lived during the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

. The stem

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Ichthyosauriformes was in 2014 defined by Ryosuke Motani and colleagues as the group consisting of all ichthyosauromorphs that are more closely related to ''

Ichthyosaurus communis ''Ichthyosaurus'' (derived from Greek () meaning 'fish' and () meaning 'lizard') is a genus of ichthyosaurs from the Early Jurassic (Hettangian - Pliensbachian) of Europe (Belgium, England, Germany and Portugal). Some specimens of the ichthyo ...

'' than to ''

Hupehsuchus nanchangensis ''Hupehsuchus'' is an extinct genus of small marine reptiles, about 1 m (3 ft) long, found in the area of Hubei in China. This marine reptile lived in the Olenekian stage of the Early Triassic period. It was probably a filter feeder, ...

''. 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 ...

include the possession of a long

nasal bone The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...

, stretching to the front beyond the nostril; large scleral rings, filling the eye sockets; a narrow snout in top view; and converging digits with little space between them. The Ichthyosauriformes probably split off in the

Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between 251.9 Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which ...

, about 250 million years ago; the last known forms lived in the middle

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

. A basal ichthyosauriform is ''

Cartorhynchus ''Cartorhynchus'' (meaning "shortened snout") is an extinct genus of basal (phylogenetics), early ichthyosauriformes, ichthyosauriform marine reptile that lived during the Early Triassic epoch (geology), epoch, about 248 million years ago. The g ...

''; more derived species are part of the

Ichthyopterygia Ichthyopterygia ("fish flippers") was a designation introduced by Richard Owen, 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 ...

which again include the

Ichthyosauria Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on foss ...

References

Literature

*Motani, R., Jiang, D.-Y., Chen, G.-B., Tintori, A., Rieppel, O., Ji, C., and Huang J.-D., 2014, "A basal ichthyosauriform with a short snout from the Lower Triassic of China", ''Nature''. doi:10.1038/nature13866 {{Taxonbar, from=Q18534271 Mesozoic reptiles Olenekian first appearances Turonian extinctions Ichthyosauromorpha Fossil taxa described in 2014