274 
A.R.I. Cruickshank, J.A. Long 
Figure 15 Leptocleidus clemai sp. nov., WAM 94.1.6-95, 
humerus in anterior (A), dorsal (B), 
proximal (C) and distal (D) views. 
leaving only the polycotylid pliosaurs as the last 
remaining representatives of the Pliosauroidea 
(Benton 1993). It is worth noting in this respect that 
the first mosasaurs are known from the 
5cm 
Figure 16 Leptocleidus clemai sp. nov. A, WAM 92.8.1- 
66, right tibia in dorsal view. B, WAM 
92.6.1-67, right fibula of in dorsal view. 
Scale bar = 1 cm. 
Cenomanian, about the same time as ichthyosaurs 
become extinct worldwide (Benton 1993), and may 
have been able to out-compete the pliosaurs in 
some way not yet known. Maybe they were the 
more capable swimmers (Massare 1988). They 
certainly had a very different feeding mechanism. 
But the puzzle is, if the large pliosaurids 
disappeared, then why not the cryptoclidids and 
elasmosaurs? Both of these families survived right 
to the end of Cretaceous times (Cruickshank and 
Fordyce in prep.). 
Leptocleidids are known to occur in association 
with other shallow marine to fluvial vertebrate 
assemblages. In the English Wealden, a lagoonal 
deposit, remains of L.superstes occur with terrestrial 
dinosaurs (e.g., Hypsilophodon, Iguanodon, 
Baryonyx). In South Africa L. capensis occurs in an 
inshore marine to lagoonal deposit whose 
foraminifera have a heavy nonmarine imprint, and 
remains of terrestrial dinosaurs and wood also 
occur in close association. In South Australia the 
Early Cretaceous deposits of Coober Pedy and 
Andamooka containing Leptocleidus sp. (the famous 
"Eric" specimen at the Australian Museum, 
Sydney) also yield the remains of terrestrial 
Figure 17 Attempted reconstruction of Leptocleidus clemai sp. nov. by J.Long. 
