(235 ma, MiddleTriassic)
Fig. 68. Body plans of seven ichthyosaurs, representing the four basic plans and intermediates. A) Utatsusaurus hataii (from Motani
et al. [1998]); B) Chaohusaurus geishanensis; C) Cymbospondylus petrinus (based on Merriam [1908]); D) Mixosaurus cornalianus;
E) Califomosaurus perrinv, F) Temnodontosaurus platyodon; G) Ophthalmosaurus icenicus (based on Motani et al. [1999]). A-B) basal
plan; C) stem plan; D) mixosaur plan; E) transitional; F-G) parvipelvian plan. Only known skeletal parts are figured (e.g., the neural
spines in T. platyodon are not absent but unknown), and the body outlines are hypothetical. Reconstructions are based on photographs
and measurements, and on consideration of three-dimensional directions, as pointed out by Andrews (1915). Kirton (1984) revived the
view of Andrews (1915), who criticized his own previous reconstruction (Andrews, 1910). Note that this latter reconstruction is still
widely reproduced despite of the noted inaccuracy (e.g., Sander [2000] and Buchholtz [2001]).
(200 ma, Early Jurassic)
Ophthalmosaurus icenicus
(150 ma, Late Jurassic)
Mixosaurian plan
(Fig. 68D)
The mixosaurian plan is known only for Mixosaurus, which
probably did not grow much longer than 2 m. There are
many skeletons available for this genus, so this body plan
is reasonably well known. The skull was relatively large.
There are some 50 presacral vertebrae, but the trunk is not
slender, in part due to its characteristically high neural
spines. The trunk vertebral centra are discoidal, with
height/length ratios of about 1.6 to 2.0 near the pelvic
girdle. In addition to the anticlination of the neural spines,
the caudal peak is associated with the increase of the
height of the vertebral centra posteriorly. The caudal centra
posterior to the caudal peak have a high height/length
ratio because of this height increase, often exceeding 4.0.