Systematic Paleontology
Diagnostic characters given in italics are not strictly apo-
morphic for the taxon in question; they were provided
solely for convenience.
1. Recognized Genera and Species
Superorder Ichthyopterygia Owen, 1840
Definition: The last common ancestor of Ichthyosaurus
communis, Idtatsusaurus hutiiii, and Paruinatator wapitiensis,
and all its descendants.
Diagnosis: Posterior process of postfrontal present; anterior
terrace of upper temporal fenestra present (lost in
derived forms); supratemporaT process of parietal long;
interpterygoidal vacuity absent or extremely reduced; ec-
topterygoid absent; metacarpal I with reduced anterior
shaft; metacarpal V without postaxial shaft; digits integrated
without interdigital separation; caudal peak of vertebral
column present; antidination of neural spine present
in tail.
Remarks: Maisch & Matzke (2000) claimed that Thaisaurus
was outside the clade Ichthyopterygia as defined by
Motani (1999B). However, this genus was coded on the
basis of illustrations of unprepared specimens, and its
status is very questionable. See the Phytogeny chapter for
further discussion. See also below for Thaisaurus chonglak-
manii.
Family incertae sedis
G en u s Thaisaurus M azin, Su t e e th o en , B uf fe ta u t ,
Ja eg e r e t H e lm c k e -Ingavat, 1 9 9 1
Thaisaurus Mazin et al., 1 9 9 1 :1 2 1 1
Type species: Thaisaurus chonglabnanii Mazin e t al., 1991.
Diagnosis: Pointed tooth crowns without ornamentation;
deep bu t incomplete dental alveoli (Mazin e t al., 1991).
Thaisaurus chonglabnanii Mazin, SuteeihoiSÇ Buffetaut,
Jaeger e t H elmcke-Ingavat, 1991
Thaisaurus chonglabnanii M azin e t al., 1991: 1211
Holotype: TF2454, a partial skeleton comprising skull,
forelimb, and hindlimb.
Diagnosis: As for the genus.
Occurrence: Khao Thong Hill, near Phattalung, Southern
Peninsula, Thailand.
Stratigraphic range: Unrecorded horizon of the Triassic
(probably Lower Triassic).
Discussion: Thaisaurus chonglabnanii is poorly known
because the holotype is unprepared (Mazin et al., 1991).
A color photograph of the type, kindly provided by Dr.
Mazin, reveals that the animal is very similar to a young
Chaohusaurus; no clear difference could be detected. The
ulna, as figured by Mazin et al. (1991), appears slightly
different from that of Chaohusaurus in having a broad shaft,
but the color photograph shows that the shaft is actually
constricted (brown area represents the broadened part of
the figured ulna, whereas the constricted shaft is gray as in
other bones of the specimen). Posterior teeth are not exposed
in the specimen, and thus it is not possible to see if
there is at least one rounded tooth, as in Chaohusaurus.
Proper preparation of the holotype is necessary to enhance
our understanding of this species.
Family Parvinatatoridae nov.
Remarks: A family comprising a single genus named solely
for classificational convenience.
G e n u s Paruinatator N ich o l l s e t B r in km a n , 1 9 9 5
Parvinatator Nicholls & Brinkman, 1995: 522
Type species: Parvinatator wapitiensis Nicholls & Brink-
man, 1995.
Diagnosis: Small ichfhyopterygian with total length probably
1 m or less; tooth size-relative to skull width not typically
small (more than 0.1); tooth crowns mesiodistally compressed;
more than five phalanges in longest digits.