Palæos:		Unit 210: Eureptilia
The Vertebrates		500: Thunnosauria

Eureptilia: Thunnosauria

REPTILOMORPHA
|--SYNAPSIDA
`--+--ANAPSIDA
   |
   Eureptilia
   |--Protorothyrididae
   `--Diapsida
      |--Araeoscelidans
      `--Neodiapsida
         |--Younginiformes
         `--+--Ichthyosauria
            |  |--Shastasauria
            |  `--Thunnosauria
            |     |--Stenopterygius
            |     `--+--Ichthyosaurus
            |        `--Ophthalmosauria
            `--Sauria
               |
               |--LEPIDOSAUROMORPHA
               `--ARCHOSAUROMORPHA            

Taxa on this Page

1. Ichthyosaurus X
2. Ophthalmosauria X
3. Sauria
4. Stenopterygius X
5. Thunnosauria X

Thunnosauria: Chacaicosaurus

Range: Late Triassic, but mostly Early Jurassic to middle Cretaceous

Phylogeny: Parvipelvia: Temnodontosaurus + Eurhinosauria + *: Stenopterygius + (Ichthyosaurus + Ophthalmosauria).

Characters: diapophyses & parapophyses round [S97]; diapophysis on anterior spine attaches to neural arch & moves down centrum to fuse with parapophysis in sacral vertebrae [S97]; parapophysis also moves ventrally, but not as much; caudal vertebrae with 1 articular facet [S97]; pubis & ischium rod-like [M97]. 

References: McGowan (1997) [M97]; Sander (1997) [S97].

Note: It will be disappointing if this turns out not to be a clade, since it is so aptly named.  These are, indeed, the tuna-lizards. ATW020517.

Stenopterygius: S. quadriscissus Quenstedt

Range: Early Jurassic to Middle Jurassic of Europe & South America.

Phylogeny: Thunnosauria: (Ichthyosaurus + Ophthalmosauria) + *.

Characters: to 2-3 m; generally similar to Ichthyosaurus; small head; see image for unusual structure of skull; exceptionally large orbit compared to size of head; dramatic overbite; narrow paddles (hence the name). 

Image:  fossil replica image from www.fossilien.de.  Larger image and various close-ups at this site.

Links: Prehistoric World Images - Stenopterygius - Jurassic reptile; Stenopterygius; Stenopterygius quadriscissus; Weight; Biology 356 (detail of forelimb); jurassic images (another strikingly beautiful image from Doug Henderson); Dinosaurios: Stenopterygius; Fossilienverkauf (remarkable selection of photos); Gallery of fossil amphibians, reptiles and birds; Bernstein, Fossilien, Ammoniten, Repliken und vieles mehr zum Kaufen; Neuigkeiten aus der Wissenschaft; Bilder aus der Fossilien-Sammlung von Armin Bauer; Ichthyosaur Stenopterygius quadriscissus (fossil image); Stenopterygius　ステノプテリギウス (model); Dinowelt-Stenopterygius; Ichthyosaurier Stenopterygius quadriscissus Quenstedt - ... (fossil images); [스테노프테리기우스(Stenopterygius)] (Korean: several good images); Gallery of fossil amphibians, reptiles and birds (very nice, but tiny image); 標本解説　ステノプテリギュウス.   ATW020517.

Ichthyosaurus: 

Range: Late Triassic(!?) to Early Jurassic of Europe & North America. [C97a]

Phylogeny: Thunnosauria:: Ophthalmosauria + *.

Characters: ~2 m; jaws of equal length; maxilla relatively small [M97]; orbits enlarged [M97]; narrow posorbital region [M97]; pronounced dorsal fin; nares very close to orbits; polydactyly;  

Ichthyosaurus intermedius
Lower Lias (Hettangian) of England
Length: usually less than 2 metres
The earliest species of the important Ichthyosaurid family, I. intermedius is sometimes included under the same species as the common Sinemurian I. communis.  But in view of the millions of years that separate the two, the smaller size of the former, and different flipper proportions, it is more likely that these two are different species of an ecological and evolutionary succession, with I. intermedius being the direct ancestor of I. communis.

Ichthyosaurus communis Conybeare 1821
Lower Lias (Sinemurian), Lyme Regis, Dorset
Length: usually not more than 2 metres, although occasionally up to 3 or 5 metres in length
A common, dolphin-sized ichthyosaur.  Both the dorsal (back) and tail-fins are large and shark-like.  As with all species of the genus, the jaws are of equal length, the teeth extending in a regular series along the whole length of the mouth [Zittel, p.280].  Both flippers are quite short and broad, the fore-flippers being much larger than the hind ones.

Ichthyosaurus conybeari Lydekker 1888
Lower Lias (Sinemurian), Lyme Regis, Dorset
Length: about 1 metre
A relatively rare species, with a thin pointed snout equipped with numerous needle-sharp teeth.  The eyes are quite large.  The smallest ichthyosaur of this period, no larger than the Triassic mixosaurs.  [M91]

Ichthyosaurus breviceps Owen 1881
Lower Lias (Sinemurian), Lyme Regis, Dorset
Length 1.5 to 2 metres
The very short snout and large eyes give the head of this little ichthyosaur a bird-like appearance [M91].  MAK991007.

Links: Ichthyosaurus teunuirostris (Italian); No. 973: Owen's Ichthyosaurus; The Field Museum of Natural History Ichthyosaurus; Marine Reptiles: Ichthyosaur: Ichthyosaurus; Ichthyosaure - Reptile marin de l'Ere Secondaire; Dinosaurios: Ichthyosaurus; Hawkins 1834 - Page 14 - The Ichthyosaurus Chiroligostinus (not certain this is Ichthyosaurus itself, but an incredible site all the same). 

References: Callaway (1997a) [C97a]; McGowan (1991) [M91]; McGowan (1997) [M97]. ATW020517.

Ophthalmosauria: Aegirosaurus, Brachypterygius, Caypullisaurus, Nannopterygius, Ophthalmosaurus, Otschevia, Paraophthalmosaurus, Platypterygius, Plutoniosaurus, Simbirskiasaurus, Undorosaurus

Range: Middle Jurassic to Late Jurassic 

Phylogeny: Thunnosauria:: Ichthyosaurus + *.

Characters: extra zeugopodial element anterior to radius, with associated extra digit. 

Links: Charmouth 180 million years BC and the Ichthysaur.; Geology Field Trip Guide - Kimmeridge, Dorset - Kimmeridge Clay Fossils; BBC - Walking with Dinosaurs - Fact Files; Discovery of the ichthyosaur Ophthalmosaurus (Reptilia) in the Late Jurassic of the Boulonnais; Ophthalmosaurus sp.; Ophthalmosaurus (Portuguese); Dinosaurios: Ophthalmosaurus (Spanish); Diving; Untitled Document (JVP abstract); Re- NEW RHYNCHOSAUR & TEMNOSPONDYLS (questioning monophyly). ATW030613.

Sauria: LCA all living diapsids [C97a]

Range: from the Middle Permian. 

Phylogeny: Neodiapsida:::: Ichthyopterygia + *: Archosauromorpha + Lepidosauromorpha.  

Characters: Ant. process of squamosal narrow; squamosal largely restricted to top of skull; dorsal origin of temporal musculature; no tabular; sacral ribs lateral orientation; ribs mostly single-headed; fusion of caudal ribs, small proximal carpals & tarsals. 

References: Callaway (1997a) [C97a] ATW990911.

checked ATW050512