Size comparison of the Lower Cretaceous Australian leptocleidid plesiosaur Umoonasaurus demoscyllus. Unknown regions were restored after Leptocleidus and Brancasaurus. The diver silhoutte is from File:Scuba33.jpg, which is by NOAA and in the public domain.
References
Kear, B. P.; Schroeder, N. I.; Lee, M. S. (2006). "An archaic crested plesiosaur in opal from the Lower Cretaceous high-latitude deposits of Australia". Biology letters 2 (4): 615–619. DOI:10.1098/rsbl.2006.0504.
Cruickshank, A. R.; Long, J. A. (1997). "A new species of pliosaurid reptile from the Early Cretaceous Birdrong Sandstone of Western Australia". Records of the Western Australian Museum 18: 263-276.
Sachs, S.; Hornung, J. J.; Kear, B. P. (2016). "Reappraisal of Europe’s most complete Early Cretaceous plesiosaurian: Brancasaurus brancai Wegner, 1914 from the “Wealden facies” of Germany". PeerJ 4: e2813. DOI:10.7717/peerj.2813.
Own work
Slate Weasel