Utatsusaurus hataii (Shikama, Kamei and Murata 1978) Early Triassic ~245 mya, ~3 m in length, is a basal ichthyosaur derived from a sister to Shastasaurus pacificus.and Xinminosaurus. Utatsusaurus was more completely modified toward an aquatic existence and phylogenetically preceded the other ichthyosaurs. Grippia was a sister taxon. Mikadocephalus was derived from a sister to Utatsusaurus.

Overall larger and distinct from Ximinosaurus, the skull of Utatsusaurus had a longer, lower rostrum filled with more and smaller teeth. The postorbital region was taller and the upper temporal fenestrae opened dorsally on a flatter skull roof. The naris was reduced to a slit. The lacrimal was longer. The squamosal was deeper.

The cervicals were greatly shortened and there were fewer of them. The caudal neural spines raised the central portion of the tail into a short caudal fin. The dorsal ribs were longer and more gracile. Chevrons were vestigial to absent.

As in Hupehsuchus, the hindlimb was smaller than the forelimb. The pelvis was likewise reduced. Digit V, including metatarsal V, had disc-like elements.

Maisch (2010) found that ichthyosaurs nested either with mesosaurs or procolophonids. The second result is an obvious error caused by too small of an inclusion set.

Maisch MW 2010. Phylogeny, systematics, and origin of the Ichthyosauria - the state of the art. Palaeodiversity 3: 151-214.

Motani R, You H and McGowan C 1997. Eel-like swimming in the earliest ichthyosaurs. Nature, 382:347–348.

Motani R, Minoura N and Ando T 1998. Ichthyosaur relationships illuminated by new primitive skeletons from Japan. Nature, 393:255–257.

Motani R 1999. Phylogeny of the Ichthyopterygia. Journal of Vertebrate Paleontology 19(3):473-496.'

Shikama T, Kamei T and Murata M 1978. Early Triassic ichthyosaurs, Utatsusaurus hataii gen. et sp. nov., from the Kitakami Massif, Northwest Japan. Science Report of the Tohoku University Sendai, Japan, second series (Geology), 48: 77–97.

Young CC and Dong ZM 1972. On the aquatic reptiles of the Triassic in China. Vertebrate Paleontology Memoire 9:1-34

wiki/Utatsusaurus