ichthyosaur phylogeny
a mirror of some the content of Ryosuke
Motani's
excellent webpage
on Ichthyosaurs
in memory of Australia's Ichthyosaur hunter Mary Wade 1928-2005
7. PHYLOGENY AND STRATIGRAPHY OF ICHTHYOSAURS
Many ichthyosaurs are known only from
fragmentary material and unsuitable for phylogenetic analyses at the
moment. When choosing 27 better-known taxa, a phylogenetic analysis
gave the following strict consensus tree. See Motani
(1999) for details of the analysis.
There have been other studies of ichthyosaurian phylogeny since Motani (1999). I will deal with them in the future.
STRATIGRAPHY
When adding the time scale to the phylogeny, we see a certain pattern in the evolution of ichthyosaurs. Ichthyosaurs were quite diverse by the end of the Early Triassic. By early Late Triassic, there already were forms approaching the typical body profile seen in truly fish-shaped ichthyosaurs. So, the fish-shaped body plan, which, persisted for about 140 million years once established (until the extinction of the group>, evolved somewhat quickly (within 20 million years or less).
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