Utatsusaurus
Name:
Utatsusaurus
(Utatsu lizard).
Phonetic: Oo-tot-soo-sore-us.
Named By: Shikama, Kamei & Murata -
1978.
Classification: Chordata, Reptilia,
Ichthyopterygia.
Species: U. hataii (type).
Diet: Piscivore.
Size: 3 meters long.
Known locations: Japan, Canada.
Time period: Olenkian of the Triassic.
Fossil representation: Few specimens.
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.
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