| Ichthyopterygians | |
|---|---|
 | |
| Utatsusaurus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | †Ichthyosauriformes |
| Superorder: | †Ichthyopterygia Owen, 1840 |
| Subgroups | |
Ichthyopterygia ("fish flippers") was a designation introduced bySir Richard Owen in 1840 to designate the Jurassicichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitive early and middleTriassic ancestors.[1][2]
Basal ichthyopterygians (prior to and ancestral to true Ichthyosauria) were mostly small (a meter or less in length) with elongated bodies and long, spool-shapedvertebrae, indicating that they swam in a sinuous,eel-like manner. This allowed for quick movements and maneuverability that were advantages in shallow-water hunting.[3] Even at this early stage, they were already very specialised animals with proper flippers, and would have been incapable of movement on land.
These animals seem to have been widely distributed around the coast of the northern half ofPangea, as they are known from theOlenekian (Early Triassic) and earlyAnisian (earlyMiddle Triassic) ofJapan,China,Canada, andSpitsbergen (Norway). By the later part of the Middle Triassic, thestem group members were extinct, having been replaced by their descendants, the true ichthyosaurs.
Fossil remains of derived marine ichthyopterygians, and the oldest ichthyopterygian remains to date, are known from the Olenekian agedVikinghøgda Formation of Spitsbergen (Svalbard). These rocks are dated to just 2 million years after thePermian-Triassic extinction event, indicating that ichthyopterygians at the very least originated very early in the Triassic, before theLate Smithian crisis (a widespreadocean anoxic event that may have allowed ichthyopterygians to dominate deeper waters andtemnospondyls to dominate shallow waters) and thatichthyosauromorphs as a whole originated during thePermian and were survivors of the Permian-Triassic mass extinction.[4][5]
Below is acladogram modified from Cuthbertsonet al., 2013.[6]
| Ichthyopterygia |
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