Western Australian Cretaceous pliosaurid 
267 
SYSTEMATIC PALAEONTOLOGY 
Class Reptilia 
Subclass Sauropterygia Owen, 1860 
Order Plesiosauria de Blainville, 1835 
Superfamily Pliosauroidea (Gray, 1825) Welles, 
1943 
Family Pliosauridae Seeley, 1874 
Genus Leptocleidus Andrews, 1922 
Type species 
Leptocleidus superstes Andrews, 1922 
Emended diagnosis 
Leptocleidus can be defined as a small genus of 
pliosauroid possessing cranial and postcranial 
characters of a conservative kind, being in many 
ways no more derived than the Liassic (Early 
Jurassic) genera Eurycleidus and Rhomaleosaurus 
(Andrews 1922; Cruickshank 1994, 1996a; Taylor 
1992). Skull triangular in outline, with a prominent 
midnasal ridge which merges with the parasagittal 
crest, flanked by deep grooves or depressions 
which in turn cause the orbital rims to stand up 
from the general profile of the skull. Compared 
with Rhomaleosaurus the tooth count is reduced, to 
21 positions on each side of the upper jaw (5 in 
each premaxilla + 16 in each maxilla), compared 
with at least 27 in the upper jaw of R. megacephalus 
(Cruickshank 1994), and a similar number in R. 
zetlandicus (Taylor 1992; Cruickshank 1996a). No 
complete jaw is known for the genus, but an 
estimated tooth count is 35 (L. capensis), at the 
lower end of the known range for pliosaurids. A 
spatulate lower jaw symphysis with five pairs of 
teeth is assumed for L.capensis (Cruickshank 1997). 
Leptocleidus possesses a dorsomedially directed 
trough on the prearticular and adjacent bones of 
the lower jaw, similar to Rhomaleosaurus. Pectoral 
girdle primitive, having large clavicles and 
interclavicles and small scapulae (Andrews 1922); 
humerus has a very much more symmetrical (fan¬ 
shaped) distal end, in contrast to Rhomaleosaurus 
which has the humerus gently curved posteriorly 
(Cruickshank 1996a; in press). None of the 
vertebrae are compressed, cervicals being spool¬ 
shaped with the neural arches relatively large 
when compared with, for example, Pliosaurus 
brachyspondylus (Taylor and Cruickshank 1993). 
Cervical vertebral count in excess of 13. Leptocleidus 
differs from early forms in one other feature in 
Figure 4 Leptocleidus clemai sp. nov. Anterior cervical 
vertebra of WAM 94.1.6- 64, in anterior (A), 
left lateral (B) and ventral (C) views. Scale 
bar = 1 cm. Abbreviations: fna, fossa for 
neural arch; fcer, attachment of cervical rib. 
possessing a forwardly-pointing expansion 
('cockscomb') on the squamosal mid-line, at the 
rear of the parasagittal crest, very similar to that 
seen in Late Cretaceous Polycotylidae (Welles 1962; 
Thurmond 1968). 
Remarks 
The genus has been redefined in the light of new 
material plus observations of undescribed 
specimens made by one of us (ARIC). We consider 
it important to include this here as further new 
specimens of the genus have been uncovered 
throughout eastern Australia which we anticipate 
will be described in the near future. It should be 
noted that jaw morphology and possibly the 
humerus and cervical vertebral morphology and 
count follow closely those of Early Jurassic genera 
such as Rhomaleosaurus. This is unusual in that it is 
usually recognised that by the Late Jurassic 
pliosaurs reduced their neck vertebral count to 13 
highly compressed disc-like centra. The presence 
Figure 3 Leptocleidus clemai sp. nov. Holotype 92.8.1. A-E, cervical vertebra 92.8.1-29, seen in anterior (A), posterior 
(B), left lateral (C), dorsal (D) and ventral (E) views. F-H, J, M, postcervical vertebra, 92.8.1-23 in left lateral 
(F), anterior (G), posterior (H), dorsal (J) and ventral (M) views. I, K,L,N,0, caudal vertebra 92.8.1-33 in 
posterior (1), dorsal (K), anterior (L), left lateral (N) and ventral (O) views. All shown natural size. 
