Utatsusaurus: Research Database
Utatsusauroidea (Ichthyosauria) · Early Triassic (~250–245 MYA) ·> Asia — Japan (Matsuda, Gifu Prefecture)
Research Note: Utatsusaurus was an early ichthyosaur from the Early Triassic of Japan. As one of the earliest known ichthyosaurs, it provides critical data on the origin and early diversification of ichthyopterygians.
| Research Finding | Status | Grade | Year | Method | Citation | Impact |
|---|---|---|---|---|---|---|
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Maisch & Matzke 2003: Utatsusaurus and early ichthyosaur evolution in the Triassic of Japan
Maisch & Matzke 2003 provide comprehensive data on Utatsusaurus from the Early Triassic of Japan, establishing it as a basal ichthyosauromorph and documenting its significance for understanding the early evolution of ichthyopterygians
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Confirmed | A | 2003 | Fossil | Maisch & Matzke, Neues Jahrbuch für Geologie und Paläontologie | Taxonomy |
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Motani 1996: New data on early ichthyosaur evolution
Motani 1996 provide additional data on early ichthyosaur evolution, contextualising Utatsusaurus within the broader evolutionary history of ichthyopterygian marine reptiles
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Confirmed | B | 1996 | Fossil | Motani, Journal of Vertebrate Paleontology | Evolution |
Active Debate: The Origin of Ichthyopterygians and Early Marine Reptile Evolution
Whether Utatsusaurus is a basal ichthyosauromorph or more closely related to true ichthyosaurs is debated.
What We Still Do Not Know About Utatsusaurus
- Complete skeletal morphology: Partial specimen known.
- Body size: Estimated.
- Swimming mechanics: Locomotion debated.
- Diet: Likely fish-eating.
In Depth
Utatsusaurus is an important entry in the fossil record concerning marine reptiles as it is often considered one of the first ichthyosaurs and as such it is used by some as the bench mark for identifying basal (primitive) features in ichthyosaurs. This includes skeletal features similar to diapsid reptiles, today the group that includes lizards that dates back as least as far as the Carboniferous with the appearance of Petrolacosaurus. Utatsusaurus was not as well developed to aquatic life as later ichthyosaurs were as it lacked a dorsal fin, and had a tail that seems to have bent down to a larger lower lobe that resulted in an uneven caudal tail.
Utatsusaurus may not have been ‘the’ defining primitive form however as the fins have four toes instead of the usual five seen in other primitive ichthyosaurs. This suggests that Utatsusaurus was on the evolutionary line to transitionary ichthyosaurs such as Mixosaurus which had three toes indicative of advanced forms like Ichthyosaurus. For this reason alone Utatsusaurus remains an important entry when dealing with ichthyosaur evolution. The limelight has shifted away from Utatsuaurus somewhat since the 2015 naming of Cartorhynchus.
The skull of Utatsusaurus is quite broad in proportion when compared to other ichthyosaurs (especially narrow skulled ones like Shastasaurus), and is a feature that harks back to its terrestrial ancestors. Teeth in the jaws suggests that Utatsusaurus hunted for fish, although its plausible that Utatsusaurus may have taken other prey such as cephalopods and possibly even other smaller marine reptiles.
Further Reading
– Early Triassic Ichthyosaurus, Utatsusaurus hataii Gen. et Sp. Nov., from the Kitakami Massif, Northeast Japan. – Science Reports of the Tohoku University Second Series (Geology), 1977. 48(1–2): p. 77-97. – T. Shikama, T. Kamei & M. Murata – 1977. – Redescription of the dental features of an early Triassic ichthyosaur, Utatsusaurus hataii. – Journal of Vertebrate Paleontology, 1996. 16(3): p. 396-402. – R. Motani – 1996. – New information on the forefin of Utatsusaurus hataii (Ichthyosauria). – Journal of Paleontology, 1997. 71(3): p. 475-479. – R. Motani – 1997. – Ichthyosaurian relationships illuminated by new primitive skeletons from Japan. – Nature, 1998. 393(6682): p. 255-257. – R. Motani, N. Minoura & T. Ando – 1998. – Reinterpretation of the cranial morphology of Utatsusaurus hataii (Ichthyopterygia) (Osawa Formation, Lower Triassic, Miyagi, Japan) and its systematic implications. – Journal of Vertebrate Paleontology, 2013. 33(4): p. 817-830. – R.S. Cuthbertson, A.P. Russell & J.S. Anderson – 2013.
