|The Vertebrates||Ancestral Ichthyosaurs|
illustration by Nobu Tamura (Wikipedia)
Ichthyopterygia ("fish flippers") was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic Ichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitive early and middle Triassic ancestors (Motani 1997, Motani et al. 1998, Motani 1999b).
Basal Ichthyopterygians (prior to and ancestral to true Ichthyosauria) were mostly small (a meter or less in length) with elongate bodies and long spool shaped vertebrae, indicating that they swam in a sinuous eel-like manner. This allowed for quick movements and maneouverability that were an advantage in shallow-water hunting (Motani 2000). Even at this early stage they were already very specialised animals with proper flippers, and would have been incapable of movement on land.
These animals seem to have been widely distributed around the coast of the northern half of Pangea, as they are known the Late Olenekian and Early Anisian of Japan, China, Canada, and Spitsbergen (Norway). By the later part of the Middle Triassic they were extinct, having been replaced by their descendents, the true ichthyosaurs. MAK060529 (Wikipedia)
Range: Early Triassic to Late Cretaceous
Phylogeny: Neodiapsida:::: Sauria + *: Utatsusaurus + (Grippidia + Ichthyosauria)
Characters: euryapsid skull; primitive tooth implantation probably subthecodont [M97]; replacement teeth outside pulp cavity [M97]; uniquely down-turned vertebral column that enters the lower lobe of its caudal fin; flippers for limb; live birth.
Links: Dinosauricon; JVP; Notes; CVA; Wikipedia, Ichthyosaurs.
Image: Utatsusaurus from [M+98].
References: Motani (1997) [M97]; Motani et al. 1998) (M+98) (image). ATW020518.
Range: Early Triassic of Japan & Canada
Phylogeny: Ichthyopterygia: (Grippidia + Ichthyosauria) + *.
|Utatsusaurus from Fossil Gallery. Note that the forelimbs show a characteristic ichthyosaur pattern of polyphalangy, but are very small. The dorsal vertebrae are narrow and relatively long.|
Characters: 1.4 - 3.0 m "lizard with flippers"; lower temporal fenestra absent [M+98]; tooth implantation pleurodont anteriorly, shifting to subthecodont [M97]; replacement teeth are lingodistal to functional tooth [M97]; tooth roots expanded [M97]; body relatively long and thin; about 40 small diameter, cylindrical vertebrae (undulatory swimming) [M+98]; 2 well-defined sacral (but transversely thin and weakly articulated with ilium) ribs with distal expansion [M+98]; sacral ribs not fused to vertebrae [M+98]; small flippers; humerus & femur of equal length [M+98]; hindlimb larger than forelimb [M+98]; restricted to continental shelf
Links: Fish-lizards; Fossil Gallery; JVP; Utatsusaurus; Utatsusaurus Japanese); Ordnung der Ichthyosauria German -- probably an excellent page); Tohoku MNH; Yamagata Japanese: excellent photo); Utatsusaurus ??????? ???? Japanese models); ??????? Korean); 05.20.98 - UC Berkeley study establishes that extinct ... press release); The Journal of Vertebrate Paleontology abstract); Scientific American- Feature Article- Rulers of the Jurassic Seas ... also in Polish); 07.15.98 - "Fish-Lizards" Turn Out to Be More Lizard than Fish press release); The Journal of Vertebrate Paleontology another abstract); ?? fossil); Dan Varner Paleo-Life Art Dan's image of Utatsusaurus); ???.
References: Motani (1997) [M97]; Motani et al. 1998) (M+98) ATW030203.
Grippidia: Chaohusaurus (= Chensaurus), Grippia
Range: Early Triassic of Greenland, China, etc.
Phylogeny: Ichthyopterygia:: Ichthyosauria + *.
Characters: <1 m?; lacrimal excluded from nares [C97]; relatively large upper temporal fenestra [C97]; postorbital participates in upper temporal fenestra (primitive) [C97]; tooth implantation subthecodont [M97]; replacement teeth lingodistal [M97]; tooth roots expanded [M97]; dentition, vertebral number & form similar to Utatsusaurus; humerus longer than femur (as in all other ichthyopterygians) [M+98].
Image: David Peters - Reptile Evolution.
Links: Eyes; JVP; JVP.
References: Callaway (1997) [C97]; Motani (1997) [M97]; Motani et al. 1998) [M+98]. ATW021024