Western Australian Cretaceous pliosaurid 
273 
Figure 14 Leptocleidus clemai sp. nov., WAM 92.8.1-2, 
femur, in anterior (A), dorsal (B) and 
proximal (C) views. 
There is a notch developed betwen the tibia and 
fibula, which are wider than long (Figure 16). The 
ilium (Figures 12,13C) is well ossified, but its distal 
end is not preserved. 
WAM 94.1.6-1 to 100 (Figs 4, 7,13C, 14) 
The second specimen seems to be identical with 
the foregoing, so little of the corresponding 
material is illustrated. The vertebrae range in 
overall length from 20.0 mm for an anterior 
cervical (Figure 4) to 41.2 mm for a dorsal centrum 
(Figure 11). Sacral vertebrae range from 28.0 mm 
to 38.2 mm, and cervicals range in length up to 
39.7 mm. These sizes coincide with those for WAM 
92.8.1 with the exception of the anterior cervical 
vertebra, which is from a region of the neck much 
further forward than in WAM 92.8.1. 
The complete right humerus of WAM 94.1.6 
(Figures 13C, 15) is 270 mm long, 68.2 mm across 
the head and 127.4 mm across the distal expansion 
(Table 1). It does not have the preaxial expansion 
seen in other late pliosaurs, and is reminiscent of 
the humeri of Early Jurassic plesiosaurs 
(Cruickshank 1996b). 
These specimens represent two sub-adult small 
pliosaurids with an estimated maximum length 
of 2.5 to 3 m. (based on proportions of 
Rhomaleosaurus), from shallow marine waters of the 
Early Cretaceous of Western Australia, which vary 
from other known members of the genus 
Leptocleidus only in their greater size. 
DISCUSSION 
Maturity of specimens 
A question as to whether the specimens 
described here are juvenile or not deserves 
comment. The limb bones are all very well ossified 
and do not give the impression of being from 
young animals. However the neural arches of the 
two other species of Leptocleidus are firmly fused to 
their centra, and certainly these two specimens 
must be regarded as 'adult'. Notwithstanding these 
observations, the specimen of Pliosaurus 
brachyspondylus described by Taylor and 
Cruickshank (1993) is a very large animal (skull 
length ca 2m), the skull sutures were well fused, 
and yet the cervical vertebrae did not have their 
neural arches fused. It is unlikely that an observer 
would have called that animal, if seen alive, 
"juvenile'. We prefer to regard these specimens 
from the Birdrong Sandstone as being sub-adult, 
probably being close to fully grown when they 
died. 
Distribution of 'primitive' pliosauroids 
Leptocleidids (Early Cretaceous) seem to be very 
similar to, if smaller than, rhomaleosaurid (Early 
Jurassic) pliosaurs. An ancestor-descendant 
relationship can be confidently inferred for them 
(Cruickshank 1996a). They seem to have been 
inhabitants of the close-inshore, marine, 
environments in a manner similar to modem sea- 
lions, and may have moved to this environment 
under pressure from the later, larger, Jurassic 
forms such as Liopleurodon, Simolestes, Pliosaurus 
and Peloneustes (Andrews 1910 - 1913; Taylor and 
Cruickshank 1993). These large forms, in the 
Cretaceous, are typified by the genus Kronosaurus, 
but which did not survive beyond the Turonian, 
