Character Matrix and Description
1. Premaxilla posterior end - (0) concave and the dorsal process
is longer than the ventral (Fig. 2A-C); (1) pointed, barely
entering the external naris (Fig. 2D); (2) concave and the
ventral process is longer than the dorsal (Fig. 2E, G-H). Unlike
in other ichthyosaurs and basal diapsids, the premaxilla
of Mixo sauru s has a pointed posterior end that hardly enters
the anterior margin of the external naris. Mazin (1981A)
reconstructed a similar posterior end for the premaxilla of
Grippia longirostris, but this is incorrect (Motani, 1997A).
2. Maxilla dorsal lamina - (0) absent (Fig. 2E, G-H); (1) present
(Fig. 2A-D). [Maisch & Matzke, 1997: characters 2 and 3
(correlated)]
3. Maxilla-external naris contact - (0) present (Fig. 2A-D, H); (1)
absent (Fig. 2E, G) [Maisch & Matzke, 1997: character 1)]
4. External naris orientation - (0) dorso-lateral (Fig. 3A-B); (1)
lateral, barely visible in dorsal view (Fig. 3C-H).
5. Nasal-external naris contact - (0) absent; (1) present.
6. Wide contact between nasal / postfrontal - (0) absent (Fig. 3A-
B, D, F); (1) present (Fig. 3C, E-H). The two bones may be in
contact in Shasta saurus (Fig. 3F), but not as clearly as in
parvipelvians. [Maisch & Matzke, 1997: character 9].
7. Nasal-parietal contact lateral to frontal - (0) absent (Fig. 3AG);
(1) present (Fig. 3H).__.
8. Prefrontal-postfrontal contact - (0) absent, the dorsal margin
of the orbit being formed by the frontal (Fig. 2A-B); (1) present,
eliminating the frontal from the dorsal margin of the orbit
(Fig. 2C-H).
9. Postfrontal postero-lateral process - (0) absent; (1) present,
overlying the postorbital (Fig. 2A-H).
10. Postfrontal participation in UTF - (0) absent; (1) present (Fig.
3A-H).
11. Postorbital shape - (0) triradiate; (1) lunate, without posterior
process (Fig. 2A-H).
12. Postorbital participation in UTF - (0) present (Fig. 2A-B); (1)
absent (Fig. 2C-H).
13. Squamosal participation in UTF - (0) present (Fig. 2A, C, F);
(1) absent (Fig. 2B, D, G-H); (2) squamosal absent (Fig. 2E).
14. Anterior terrace of upper temporal fenestra - (0) absent (Fig.
3E, G-H); (1) present, but small, reaching the posterior part of
the frontal anteriorly (Fig. 3A-C, F); (2) present, and large,
reaching the nasal anteriorly (Fig. 3D).
15. Frontal widest position - (0) located posteriorly (Fig. 3A-D);
(1) at nasal suture (Fig. 3E-H).
16. Sagittal eminence - (0) absent; (1) present but small, involving
only the parietal; (2) present and large, involving the
parietal, frontal, and nasal. The parietals of some ichthyosaurs
(e.g., Cymbospondylus p etrin u s) are nearly vertical along
the median line, forming a small crest (Fig. 3C, F). This
eminence is reduced in some forms, but present (Fig. 3E, H).
A large sagittal crest, reaching the nasal, is a characteristic of
M ix o sauru s (Fig. 3D).
17. Parietal ridge - (0) absent (Fig. 3A-B); (1) present (Fig. 3D-E,
G-H). The parietal ridge (sensu McGowan, 1973) is a feature
that is only present in derived ichthyosaurs. Its presence or
absence has yet to be confirmed for Shasta saurus (Fig. 3F).
18. Parietal supratemporal process - (0) short (Fig. 3D-E, G-H);
(1) long (Fig. 3A-C, F).
19. Right and left parietals’ anterior processes - (0) contacting
each other anteriorly, eliminating frontal from pineal foramen
(Fig. 3A-B); (1) narrowly separated anteriorly, forming parietal
fork, and frontal dorsally visible along the pineal foramen
(Fig. 3C-D, F); (2) widely open, resulting in absence of
clear fork (Fig. 3E, G-H). [M a z in , 1982: character 2; Callaw a y ,
1989: character 2]
20. Supratemporal posterior slope - (0) absent; (1) present. In
ichthyosaurs, the supratemporal has a slope on the postero-
dorsal comer (Motani,. 1997A). This posterior slope is small
in Utatsusaurus (Motani, 1997A), but well developed in Mixosaurus
(Motani, 1997A) and in Ichthyosaurus (McGowan,
1973), forming a partial roof over the upper temporal fenestra:
21. Supratemporal posterior ridge - (0) absent; (1) present. The
posterior ridge (M o t a n i, 1997A) of the supratemporal is
present in all ichthyosaurs where a supratemporal is known
(M o t a n i, 1997A), but absent in basal diapsids.
22. Supratemporal ventral process - (0) absent; (1) present. The
ventral process of the supratemporal is known in some derived
ichthyosaurs, such as Mixosaurus (Motani, 1997A) and
Ichthyosaurus (McGowan, 1973).
23. Jugal-quadratojugal dorsal contact - (0) absent (Fig. 3A-B);
(1) present (Fig. 3C-H).
24. Jugal shape - (0) triradiate; (1) lunate, or J-shaped (Fig. 3A-H).
25. Cheek orientation - (0) mostly lateral; (1) largely posterior. In
eurhinosaurs and several other ichthyopterygians, the posterior
curvature of the cheek region is so extensive that the
region is better viewed posteriorly than laterally.
26. Pterygoid, transverse flange - (0) antero-lateral; (1) posterolateral;
(2) not well defined.
27. Interpterygoidal vacuity - (0) present; (1) absent, or extremely
reduced. [M a is c h & M atzke, 1997: character 22]
28. Ectopterygoid - (0) present; (1) absent. [Callaway, 1989: character
9]
29. Basioccipital peg - (0) clearly present; (1) absent or extremely
reduced.
30. Basioccipital extracondylar area - (0) wide; (1) reduced to a
narrow band of concavity.
31. Basioccipital condyle - (0) flat or slightly concave; (1) hemispherical.
[Callaway, 1989: character 1]
32. Angular lateral exposure - (0) extensive, at least as high and
anteriorly as surangular exposure (Fig. 3G); (1) much smaller
than surangular exposure (Fig. 3A-C, E).
33. Overbite - (0) absent or slight; (1) clearly present.
34. Snout extremely slender - (0) no; (1) yes.
35. Replacement teeth - (0) appear outside the pulp cavity of the
predecessor; (1) inside.
36. Plicidentine - (0) absent; (1) present.
37. Tooth horizontal section - (0) circular; (1) disto-medially compressed;
(2) laterally compressed.
38. Posterior tooth crown - (0) conical; (1) rounded; (2) flat.
39. Tooth size relative to the skull width - (0) normal (over 0.1);
(1) small (below 0.05). This character is based on M assare’s
(1987) index to express the size of the teeth relative to the
gullet width (substituted by skull width). There seems to be
a clear dichotomy in the distribution of this feature among
ichthyosaurs: the possession of small and numerous teeth is
typical of some Early Triassic ichthyosaurs (M o t a n i, 1996,
1997B), and Mixosaurus comalianus (M o t a n i, 1997A).
40. Maxillary tooth row - (0) single; (1) multiple.
41. Upper dental groove - (0) present throughout jaw margin; (1)
only present anteriorly; (2) absent. A dental groove, homologous
to that of the subthecodont condition in primitive am-
niotes, exists in most ichthyosaurs (M o t a n i, 1997B).
42. Lower dental groove - (0) present throughout jaw margin; (1)
only present anteriorly; (2) absent. The lower dental groove
shows a different character-state distribution than its upper
counterpart (M o t a n i, 1997B), and is therefore treated as a
separate character.
43. Bony fixation of teeth — (0) present; (1) absent.
44. Pterygoidal teeth - (0) present; (1) absent. Pterygoidal teeth
are absent from ichthyosaurs, except in Utatsusaurus hataii,
which has vestigial teeth on the pterygoid.
45. Interclavicle shape - (0) cruciform; (1) triangular; (2) T-shaped.
46. Scapula antero-dorsal margin - (0) fan-shaped (Fig. 4A-B, D-
E, G-H); (1) emarginated (Fig. 4C); (2) straight (Fig. 4F). [C a l law
ay, 1989: character 23]
47. Scapular blade shaft - (0) absent (Fig. 4A-E); (1) present at
least proximally (Fig. 4F-H). The narrow region in the scapula
of Cymbospondylus (Fig. 4C) is not considered a shaft because
the surface striation is radial, not being parallel to the margin.
48. Scapular axis and glenoid facet orientations - (0) nearly parallel
(Fig. 4A-F); (1) at 60 degrees or more (Fig. 4G-I).
49. Coracoid facet on scapula - (0) scapula and coracoid fused;
(1) absent; (2) equal or smaller than glenoid facet of scapula;
(3) twice as large as glenoid facet.
50. Ossified sternum - (0) absent; (1) present.
51. Ossified cleithrum - (0) present; (1) absent.
52. Humerus distal articular facets - (0) not terminal; (1) terminal,
radial facet being larger than ulnar facet; (2) terminal,
two facets being nearly equal.
53. Humerus anterior flange - (0) absent; (1) present and complete;
(2) present but reduced proximally. [Callaway, 1989:
character 29]
54. Humerus relative width exclusive of anterior flange — (0)
much longer than wide; (1) nearly squarish. [C a llaw a y , 1989:
character 28]
55. Humerus, distal and proximal ends, exclusive of anterior
flange - (0) nearly equal; (1) distal end wider than proximal
end.
56. Ridge on humerus plate-like - (0) no; (1) yes. The dorsal
ridge in the Ophthalmosauria are well pronounced to from a
plate-like eminence.
57. Humerus anterodistal facet for sesamoid - (0) absent; (1)
present. [Godefroit, 1993: character 10]
KÜ 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
P etro la co saurus 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ? 0 0 0 0 0 7
Thadeo saurus ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
Claudio saurus 0 1 0 0 0 0 0 Ol 0 0 0 m 0 0 0 0 1 0 0 0 i t 1 ,0i. 0 1 0 p f # 0 0 0 0 7
Hova sauru s \ ? n 7 n M . 0 0 0 0 1 0 0 0 0 9 0 0 0 ? ? 0 0 0 0 0 1 0 ? ? % 0 ? 7 7
H upesuchus 0 0 1 ? 0 0 1 0 0 ? 0 0 ! 0 ? 0 0' 0 ? ? ? ? ? ? 0 2 0 0 ? ? 7 7 0 0 ?
Utatsusaurus 0 1 0 0 0 0 0 0
p
1 0 0 1 0? 0 0 1 0 1 1 0 0 1 0 0 t i 1 ? ? ? 1 0 0 0
Grippia 0 1 0 0 0 0 0 0 1 1 1 0 1 1 0 0 0 1 0: ? ?l r 'ÜÈ 0 1 0 0 ? ? ? 7 1 0 ? 0
P a rvin ata to r I t 1 0 0 ? ? 0 ? ? 1 ? ? ? ? ? ? ? ? ? ? ? ? 1 ? ? ? ? ? ? ? ? ? ? ?
Chaohusaurus ■ ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 1 7
Cymb. petrinus 0 1 0 1 1 1 0 1 1 1 1 1 i : 1 --0! 0 l 1 ? 1 1 1 0 2 1 1 ! ? 0 1 0 0 0
Cymb. buchseri ? ? ? ? ? ? ? 1 1 7 1 1 ? ? ? 0 ? ? ? ? ? ? ? 1 ? ? ? ? ? ? ? 1 ? ? ?
Mix. cornalianus 1 1 0 1 0 0 1 1 1 1 1 1 2 2 1 0 l I s ? ? 1 1 ? 1 ? ? 1 1 7 0 1 7
Mix. atavus 1 1 0 1 0 0 0 1 1 1 1 1 1 2 i 2 1 0 l 1 1 1 ,i: 1 0 2 1 1 ? ? 7 7 7 ? 7.
Mix. nordefisk io eldii ? ? ? ? ? ? ? ? ? ? ? ? ? 2 ? ? ? ? ? ? ? ? ? ? ? 2 ? ? ? ? ? ? ? ? ?
Besanosaurus 0 0 ? ? ? ? ? ? ? 1 ? ? ? ? ? ? ? ? ? ? ? ? ? ?< ? ? ? ? ? ? 1 ? ? ?
Shasta saurus 0 ? 0 1 0 0 0 1 1 1 • p 1 0 1 i 1 E3 1 l 1 # . ? ? 1 0 2 1 1 ? 0 1 -7 0 0 7
Shonisaurus 0 ? ? ? 1 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 1 ? ? 7 0
Califo rno saurus ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?
Toretocnemus ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 ? ? ? ? ? ? ? 1 ? ? ?
H udsonelpidia ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 ? ? ? ? ? ? ? ? 0 7
Ma cgowan ia 2 0 ? 1 ? 7 ? 1 1 ? E 1 ? ? ? ? ? ? ? ? ? ? ? 1 0 ? ? ? ? ? ? 1 0 0 7
Suevoleviathan 2 0 7 1 0 1 W:> 1 1 1 1 1 f 0 l 1 l 0 l 1 ? ” ? 1 : 1 0 ? ? ? ? ? ? 1 0 0 7
Temnodontosaurus % 0 1 1 0 1 1 1 ! 1 1 1 T 0 /1 % 1 o ?a l 1 % 1 1 1 0 2 0 1 0 0 1 1 0 0 1
L eptonectes 2 0 7 1 0) ? ? 1 1 1 1 1 n 0 ? l 0 ? 1 ? ? ? 1 1 ? 0 ? ? 0 1 1 0 0 7
Excalibosaurus ? 0 7 1 0 7 ? 1 1 7 1 1 -'Wf 0 ? ? ? ? ? ? ? ? ? 1 1 ? ? ? ? 7 ? 1 1 1 ¥■
E urhinosaurus 2 0 0 1 0 7 0 ] 1 1 1 1 ? 0 ? 0 i 0 I I 1 ? ? 1 1 1 ? ? ? ? 0 1 1 1 1 ¥'
Ichthyo sau ru s 2 0 1 1 0 1 0 1 1 1 1 1 M 0 i 1 l 0 2 1 1 1 • 1 ' 1 0 2 0 t® 0 0 1 0 0 1
S tenopterygius 2 0 0/1 1 0 1 1 1 1 1 1 1 0 i 1 l 0 2 1 1 1 ;il 1 0 2 0 M ? 0 1 0 0 7
B rachypterygius 2 0 7 1 # 7 7 1 1 7 1 1 ? 0 ? ? ? ? ? ? i ? 0 ? ? ? 1 1 1 0 0 0 7
Ophthalmosaurus 2 0 1 1 0 1 0 1 1 1 1 1 % l 0 i 0 0 2 1 1 1 T 1 0 2 0 1 1 1 i 0 0 0 1
Caypullisaurus ? 0 7 1 ? ? 4| j ? ? ? 1 7 rf ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 7 7 0 7 0 7
P latypterygius 2 0 1 1 0 1 1 1 1 1 1 1 2 0 l 1 1 0 2 1 ? ? 1 ; y 0 2 ? ? ? 1 1 0 0 0 7