Ichthyosaurian relationships illuminated by new primitive skeletons from Japan

  title={Ichthyosaurian relationships illuminated by new primitive skeletons from Japan},
  author={Ryosuke Motani and Nachio Minoura and Tatsuro Ando},
The Ichthyosauria is a group of reptiles with fish-shaped bodies from the Mesozoic (65–250 million years ago),. Their secondary adaptations to aquatic life have obscured their ancestral features,, and basal ichthyosaurs, which would be expected to retain these ancestral features (plesiomorphies), are poorly represented in the fossil record. As a result, their relationships to other amniotes have been controversial for over 180 years,. New specimens of Utatsusaurus hataii from the Lower Triassic… 


Abstract Omphalosaurus is a marine reptile known from the latest Early Triassic to the Middle Triassic. It has a wide distribution in the northern hemisphere, occurring in the eastern Pacific realm,

Osteohistology of the Early Triassic Ichthyopterygian Reptile Utatsusaurus hataii: Implications for Early Ichthyosaur Biology

The first osteohistological data concerning the most basal ichthyopterygian yet known, Utatsusaurus hataii, from the Lower Triassic of Japan is presented, and the cancellous bone structure suggests adaptation to active swimming in an open marine environment.

A New Triassic Primitive Ichthyosaur from Yuanan, South China

Based on the systematic study of two fossil skeleton specimens collected from the top of the third member of the marine Lower Triassic Jialingjiang Formation of Yuanan, Hubei Province, South China, a

Reinterpretation of the Cranial Morphology of Utatsusaurus hataii (Ichthyopterygia) (Osawa Formation, Lower Triassic, Miyagi, Japan) and its Systematic Implications

The first complete description of the skull of UHR 30691 and the incorporation of data derived from it into a phylogenetic analysis retrieves a monophyletic Ichthyopterygia that is supported by 18 unambiguous synapomorphies and recovers Utatsusaurus in a basal clade with Parvinatator (united by one unambiguous feature).

A New Ophthalmosaurid (Ichthyosauria) from Svalbard, Norway, and Evolution of the Ichthyopterygian Pelvic Girdle

The Slottsmøya Member Lagerstätte ichthyosaurs are significant in that they represent a diverse assemblage of ophthalmosaurids that existed immediately preceding and across the Jurassic–Cretaceous boundary, and expand the known range in size variation of pelvic girdle elements in the clade.

Cranial Morphology and Relationships of a New Grippidian (Ichthyopterygia) from the Vega-Phroso Siltstone Member (Lower Triassic) of British Columbia, Canada

ABSTRACT In 1989, TMP 89.127.3, a basal ichthyopterygian, was collected as a counterpart slab from the Vega-Phroso Siltstone Member (Lower Triassic) of the Sulphur Mountain Formation in

Cranial morphology of Platypterygius longmani Wade, 1990 (Reptilia : Ichthyosauria) from the Lower Cretaceous of Australia.

Preparation of specimens using acetic acid and application of high-resolution X-ray computed tomographic analyses has revealed many previously unrecorded anatomical details, including the absence of a coronoid and squamosal, and the presence of well-developed epipterygoids facets on the pterygoid and parietal.

Early Triassic ichthyopterygian fossils from the Russian Far East

Ichthyopterygia is a major clade of reptiles that colonized the ocean after the end-Permian mass extinction, with the oldest fossil records found in early Spathian substage (late Olenekian, late

New Mixosaurid Ichthyosaur Specimen from the Middle Triassic of SW China: Further Evidence for the Diapsid Origin of Ichthyosaurs

Abstract Recent cladistic analyses have all suggested a diapsid origin of ichthyosaurs. However, an intermediate evolutionary stage of the lower temporal region of ichthyosaurian skull between basal

The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps

Divergence time estimates show that lepidosaurs and most other diapsids originated before the Permian/Triassic extinction event, indicating that the Triassic was a period of radiation, not origin, for several diapsid lineages.



Eel-like swimming in the earliest ichthyosaurs

The most complete specimen of the oldest known ichthyosaur, Chensaurus, is reported, representing a transition between the two body plans, and seems to be an evolutionary intermediate between the shorter-bodied terrestrial stock from which the group evolved, and advanced thunniform ICHthyosaurs.

The affinities and ecology of Triassic ichthyosaurs

The resolution of the problem of ichthyosaurian affinities has been complicated and prolonged by an emphasis on the morphology of Jurassic ichthyosaurs, some 30 to 40 m.y. younger than the earliest

Hupehsuchus, an Enigmatic Aquatic Reptile from the Triassic of China, and the Problem of Establishing Relationships

The difficulty in determining the relationship of the Hupehsuchia may be attributed to the limited knowledge of the fossil record of diapsid reptiles in the late Permian and early Triassic, as well as the great amount of convergence exhibited by secondarily aquatic reptiles.


The importance of the critical fossils seems to reside in their relative primitive‐ness, and the simplest explanation for their more conservative nature is that they have had less time to evolve.

Turtles as diapsid reptiles

The result robustly supports the diapsid affinities of turtles, and so requires reassessment of the use of turtles as 'primitive' reptiles in phylogenetic reconstruction, and illustrates the difficulties of treating groups that have extant members with peculiar morphologies that mask phylogenetic affinity.

An ichthyosaur skull from the Cretaceous of Wyoming

  • A. Romer
  • Environmental Science, Geology
  • 1968
An ichthyosaur skull from the Mowry Shale of Wyoming--the only good ichthyosaur skull so far known from the Cretaceous--is described and figured. Study of the well-preserved temporal region leads to

A case against a diapsid origin of the Ichthyosauria

The case for the diapsid origin of ichthyosaurs made by TARSITANO (1982,1983) is revisited. The skull on which TARSITANO'S original observations and hypotheses were mainly based is rediscussed and

Reptile relationships turn turtle⃛

The data are corrected and reanalysed, and it is found that Rieppel and deBraga's data actually support, rather than challenge, the traditional view.

Osteology of the Reptiles

Based on the work of Samuel Wendell Williston and Dr. W.K. Gregory, author and editor of the original title published in 1925, this volume consists of two major parts - a structure-by-structure

Interpretation of tectonically deformed fossils

Abstract Taxonomic information can be recovered from tectonically deformed fossils by analysing the strain and then restoring the fossils to their original shapes. Trilobites and graptolites are used