Fig. 79. Chacaicosaurus cayi, holotype (MOZ 5803 PV), redrawn from Fernändez (1994). A) skull. B-C) basioccipital in posterior and left
lateral views. D) forefin, depicted as left, in dorsal view. Scales each equal 100 mm, except in B) and C) (20 mm).
mately 78, and can be referred to Stenopterygius quadriscis-
sus.) As the holotype has only four digits, and the humerus
is much broader distally than proximally, with a prominent
preaxial facet, the species is provisionally referred to
Temnodontosaurus.
Five species of Temnodontosaurus are recognized here:
T. platyodon, T. trigonodon, T. eurycephalus, T. crassimanus,
and, provisionally, T. acutirostris. Maisch & Hungerbuhler
(1997) make a case for also referring Leptopterygius nuer-
tingensis H uene, 1931B to Temnodontosaurus. The holotype
of this species (SMNS 13488) comprises a partial skull,
eight vertebrae, some ribs and a coracoid. CM previously
concluded that the material was too incomplete to be determinate
(McGowan, 1979B: 128) and accordingly considered
the species a nomen dubium. But Maisch & H ungerbuhler
(1997) made the valid point that the skull possesses
a number of distinctive features that diagnose the species.
Among these features, which include many palatal characters,
is the union of the jugal with the premaxilla. They
argued that this feature only occurs in Temnodontosaurus
trigonodon (which they referred to as T. burgundiae), and is
evidence for a close relationship between die two. The
large size of L. nuertingensis, together with its long and
robust snout, numerous, large, and strongly sculptured
teeth, and the general shape of its skull, were all taken as
further evidence of its affinities with Temnodontosaurus.
However, none of the diagnostic features of Temnodontosaurus
is evident, save for its large size, and possibly its
large, unreduced teeth. Accordingly, L. nuertingensis is here
regarded a nomen dubium.
Superfamily Ichthyosauroidea nov.
Definition: The last common ancestor of Stenopterygius
quadriscissus, Ichthyosaurus communis, and Ophthalmosaurus
icenicus, and all its descendants.
Diagnosis: Forefin at least twice as long as hindfin.
Family incertae sedis
Genus Chacaicosaurus FernAndez, 1994
Chacaicosaurus FernAndez, 1994: 292
Type species: Chacaicosaurus cayi FernAndez, 1994.
Diagnosis: Forefin probably < 5 digits; ulnare smaller than
intermedium; no digital bifurcation; notching in most elements
of leading edge; humerus probably with two distal
facets, for radius and ulna; elements in longest digit <20.
Orbit small, orbital ratio < 0 .2 0 and maybe < 0 .1 5 ; snout
long, snout ratio >0.70; nares set well back, prenarial ratio
>0.55 and probably >0.60. Teeth probably lost or extremely
reduced. Basioccipital with essentially flat anterior surface,
with only an incipient peg, if at all; extracondylar area
extensive, lying ventral and lateral to condyle; condyle
clearly defined.
Remarks: In lateral view, the basioccipital is gently rounded,
as in Ophthalmosaurus, with an incipient basioccipital
peg, which is clearly seen in FernAndez (1994: fig. 3b).
However, F ernAndez described the anterior surface as
being flat, without a basioccipital peg.
Chacaicosaurus cayi FernAndez, 1994
Fig. 79
Chacaicosaurus cayi F ernAndez, 1994: 2 92
Holotype: MOZ 5803 PV, a partial skeleton comprising a
rather poorly preserved skull, atlas / axis and four cervical
vertebrae, a nearly complete forefin, and a femur.
Diagnosis: As for genus.
Occurrence: Chacaico Sur, Neuquen Province, Argentina.
Stratigraphic range: Los Molles Formation; Middle Jurassic
(lower Bajocian).
Family Ichthyosauridae BONAPARTE, 1841
G enu s Ichthyosaurus-DE la B eche e t Conybeare,
1821
Ichthyosaurus KÖNIG, 1818: 54 [nomen nudum]
Proteosaurus Home, 1819A: 209
Ichthyosaurus de la Beche et Conybeare, 1821: 562
Eurypterygius Jaekel, 1904: 32
Protoichthyosaurus Appleby, 1979: 922
Type species: Ichthyosaurus communis de la Beche e t Conybeare,
1821.
Diagnosis: Forefin with no fewer than five digits; ulnare
larger than intermedium; digital bifurcation occurs, anterior
to the primary axis; phalanges numerous and close-
packed; distal end of humerus wider than proximal end.
Pelvic girdle tripartite, without fusion between pubis and
ischium. Preflexural vertebrae <80. Basioccipital with extensive
extracondylar area and well developed basioccipital
peg (Fig. 34A-C).
Remarks: Although Proteosaurus H ome was the first available
generic name for ichthyosaurs, Home (1819A) himself
acknowledged that the name Ichthyosaurus had already
been used. Proteosaurus has seldom been referred to in the
primary literature and should be considered a nomen ob-
litum.
Ichthyosaurus communis de la Beche et Conybeare, 1821
Fig. 80; Pis. 8-9
Ichthyosaurus communis de la Beche et Conybeare, 1821:
5 94
Ichthyosaurus communis; Conybeare, 1822: 109
Ichthyosaurus intermedius C onybeare, 1822: p. 108
Ichthyosaurus chiropolyostinus H awkins, 1834: 25
Ichthyosaurus chiroparamekostinus Hawkins, 1834: 32
Polyostinus Hawkins, 1840: 12
Paramecostinus Hawkins, 1840: 15
Ichthyosaurus latimanus Owen, 1840: 123
Ichthyosaurus fortimanus Owen, 1884: 176
Ichthyosaurus communis-, L ydekker, 1889A: 41
Ichthyosaurus communis hyperdactyla Jaekel, 1911: fig. 154
Eurypterygius communis (de la Beche & Conybeare); H uene
1922: 5 [partim]
Protoichthyosaurus prostaxalis Appleby, 1979: 9 42
Protoichthyosaurus prosostealis Appleby, 1979: 9 42
Ichthyosaurus intermedius; Maisch, 1997: 4
Holotype: A partial skeleton, mentioned by DE la Beche &
Conybeare (1821: 594), comprising, “the head, with all, or
nearly all, the vertebrae in place ... .” The mandible was
said to be “1 foot 6 1 /2 inches long” (466 mm). No illustration
was given; the specimen can no longer be located and
is assumed lost. McGowan (1974B) designated BMNH
R1162 as a neotype.
Diagnosis: Preflexural vertebrae >74 <80; presacral vertebrae
>41. Snout relatively long, snout ratio >0.57; orbit not
exceptionally large, orbital ratio typically <0.26. Forefins
variable, with differences between Somerset and Dorset
specimens. Former have fewer digits, usually six or less,
with fewer elements in longest digit (typically not more
than 20); phalanges more angular than rounded; notching
usual in some preaxial elements. Dorset specimens normally
with at least 6 digits, and upward of 9; number of
elements in longest digit >25; no notching. Medium-sized,
reaching total lengths of about 2.5 m.
Occurrence: Primarily Lyme Regis, Dorset, and Street,
Somerset, England.
Stratigraphic range: The Lyme Regis material is from the
Lower Jurassic (Lower Lias; Hettangian-Sinemurian), but
the Street material is mostly latest Triassic (Rhaetian) in
age. The stratigraphic range of the species thus straddles
the Triassic-Jurassic boundary (Rhaetian-Sinemurian).
Remarks: This species is the most common Lower Liassic
ichthyosaur. The first description of Ichthyosaurus communis
is generally attributed to Conybeare (1822) (Woodward
& Sherborn, 1890; Kuhn, 1934). However, as pointed
out by McGowan (1974B), the name first became available
in 1821.
Maisch (1997) a rgu ed for the retention of Ichthyosaurus
intermedius as a separate species, on the grounds that the
partial skull figured by Conybeare (1822: pi. 17) h a s fea