-h
ICHTHYOPTERYGIA
EOICHTHYOSAURIA
ICHTHYOSAURIA
MERRIAMOSAURIA
EUICHTHYOSAURIA
PARVIF
THUNNOSAURIA[
OPHTHALMOSAURIAÏ
Petrolacosaurus
Claudiosaurus
Thadeosaurus
Hovasaurus
Hupehsuchus
Utatsusaurus
Parvinatator
Grippia
Chaohusaurus
Cymbospondylus petrinus
Cymbospondylus buchseri
Mixosaurus cornalianus
Mixosaurus atavus
Mixosaurus nordenskioeldii
Besanosaurus
Shonisaurus
Shastasaurus
Toretocnemus
Californosaurus
Macgowania
Hudsonelpidia
Suevoleviathan
Leptonectes
Excalibosaurus
Eurhinosaurus
Temnodontosaurus
Stenopterygius
Ichthyosaurus
Brachypterygius
Ophthalmosaurus
Caypullisaurus
Platypterygius
Fig. 101. Phylogenetic hypothesis of ichthyopterygian interrelationships M o t a n i (1999B).
widely available, character-taxon-matrices-based phylogenetic
analyses started to appear. The first of those was
developed by Callaway (1989), who analyzed the interrelationships
of shastasaurids (Fig. 100G). This data matrix
was later improved by Dal Sasso & Pinna (1996), by adding
the newly described Besanosaurus (Fig. 100H). These
studies assumed the monophyly of the ingroup (i.e., shastasaurids),
which turned out to be incorrect (Motani,
1999B). Maisch & M atzke (1997A) and M aisch (1998A)
also published trees for certain ichthyosaurs based on
small character-taxon matrices (Fig. 1001, J). The largest
obstacle to all of these studies was the character polarization:
as stated earlier, the proximate ichthyopterygian sister
group is unknown even today, and only limited data
regarding basal ichthyopterygians were available to these
authors. Motani’s (1998) paper on the forefin of Grippia
contained a small data matrix for some basal ichthyopterygians,
which was added simply to fulfill an editorial condition
for publication; it is not worth further discussion.
Motani and co-workers redescribed three basal ichthyopterygians
(Utatsusaurus, Grippia, and Chaohusaurus),
with additions of new specimens (Motani, 1996, 1997A,
1997B, 1998,2000A; Motani & You, 1998A, 1998B; Motani
et al., 1996, 1998). The resulting data were incorporated
into Motani’s (1999B) phylogenetic analysis of ichthyopterygians,
which, for the first time, covered the majority of
the better-known ichthyosaurs, using both cranial and
postcranial characters (27 ingroup taxa, 105 characters).
The analysis also benefited from the recently established
homology of ichthyopterygian forefin elements, which
was not available to previous studies. Caldwell (1997)
first introduced ossification sequence of carpal bones to
the identification of ichthyopterygian fin elements, which
was subsequently elaborated by Motani (1999A). As he
admitted, Motani’s (1999B) cladogram was far from definitive,
and only certain clades were found sufficiently robust
to be named (see Fig. 101). For example, all post-
Triassic ichthyosaurs formed a clade in Motani’s (1999B)
cladogram, but it was not named because of its instability.
Additional data for as yet unpublished specimens from the
Norian of Williston Lake suggest that this monophyly is
indeed not supported. Therefore, it seems best at the moment
to recognize the Parvipelvia as a major clade representing
the so-called Jurassic-type ichthyosaurs (which are
not restricted to the Jurassic and Cretaceous).
In a review article, Sander (2000) published a new tree
depicting ichthyopterygian interrelationships (Fig. 100F).
The topology presented was somewhat similar to the one
given by Mazin (1982), reflecting the traditional view of
ichthyosaurian evolution. The published data matrix lacks
seven of his characters, and it is not possible to reproduce
the results obtained by Sander (2000) from what is available.
The data matrix did not incorporate previous studies,
and therefore lacks some characters that are considered
important by other authors. Many of the characters used
by Sander (2000) were proportional, which is problematic,
as previously pointed out by Motani (1999B); it is usually
difficult to consider arbitrary divisions of proportions as
discrete synapomorphies. For example, when coding the
snout ratio, there is usually no reason to, say, subjectively
Table 5. Higher-level classification of ichthyosaurs.
Family Genus
Superorder Ichthyopterygia Family incertae sedis Thaisaurus
Family incertae sedis Isfjordosaurus
Family Utatsusauridae Utatsusaurus
Family Parvinatatoridae Parvinatator
(Eoichthyosauria)
Order Grippidia Family Grippiidae Grippia
Chaohusaurus
Order Ichthyosauria Family Cymbospondylidae Cymbospondylus
(Hueneosauria)
Suborder Mixosauria Family Mixosauridae Mixosaurus
Tholodus
Suborder Merriamosauriformes Family incertae sedis Phantomasaurus
Family Besanosauridae Besanosaurus
Family Guanlingsauridae Guanlingsaurus
(Merriamosauria)
Infraorder Shastasauria Family Shastasauridae Shastasaurus
Shonisaurus
Himalayasaurus
Infraorder Euichthyosauria Family incertae sedis Qianichthyosaurus
Family lbretocnemidae Toretocnemus
Family Califomosauridae Californosaurus
(Parvipelvia) Family Macgowaniidae Macgowania
Family Husonelpediidae Hudsonelpidia
Family Sueveleviathanidae Suevoleviathan
Superfamily Temnodontosauroidea Family Temnodontosauridae Temnodontosaurus
Superfamily Leptonectoidea Family Leptonectidae Leptonectes
Excalibosaurus
Eurhinosaurus
Superfamily Ichthyosauroidea Family incertae sedis Chacaicosaurus
Family Ichthyosauridae Ichthyosaurus
Family Stenopterygiidae Stenopterygius
Family Ophthalmosauridae Mollesaurus
Nannopterygius
Undorosaurus
Brachypterygius
Aegirosaurus
Ophthalmosaurus
Caypullisaurus
Platypterygius