Umoonasaurus demoscyllus Click to enlarge image
Umoonasaurus demoscyllus. Pliosaur opalised fossil bones nick named Eric Image: Carl Bento
© Australian Museum

Fast Facts

  • Classification
    Super Class
  • Size Range
    2.5m long (head-tail)
  • View Fossil Record
    Fossil Record
    Cretaceous Period
    (141 million years ago - 65 million years ago)

Pliosaurs are actually aquatic carnivorous reptiles, not dinosaurs. 'Eric' was a small, short-necked pliosaur and and was discovered by an opal miner in Coober Pedy in 1987. 'Eric' is one of the most complete opalised vertebrates known and became part of the fossil collection of the Australian Museum in 1993 after money to purchase the specimen was raised by the schoolchildren of Australia (with the help of Akubra Hats). 'Eric' is currently on display at the Australian Museum.


Plesiosaurs (pliosaurids and elasmosaurids) were secondarily marine tetrapods that evolved from a group of terrestrial sauropterygian reptiles during the latest Triassic. The limbs of plesiosaurs were developed into paddles, and the limb girdles formed large ventral plates akin to the plastron of turtles.

Pliosaurids were short-necked, carnivorous marine reptiles belonging to the order Plesiosauria, which also included the long-necked elasmosaurids. The skulls of pliosaurids were massive, supported by short, robust necks.

'Eric' was a very small pliosaur, only about the size of a living seal. Features unique to Eric include small body size, a comparatively long neck and a proportionately small head (other pliosaurs tended to have shorter necks and larger heads). A keel on the snout suggests that 'Eric' may have had a crest down the midline of the rostrum. There are also thin ridges of bone over the orbits (eye sockets).


'Eric' lived in the cool, high-latitude Eromanga Sea - an inland sea that covered vast areas of inland Australia during the Early Cretaceous (Aptian-Cenomanian, about120-90 million years ago). Glendonites and boulders that may have been rafted by ice are evidence of cold to near-freezing winter conditions.


'Eric' is known only from a single skeleton found at Coober Pedy in South Australia (once part of the epicontinental Eromanga Sea).

Feeding and diet

Like other small pliosaurs, 'Eric' probably subsisted mainly on a diet of fish Fish bones and gastroliths (to help regulate buoyancy) and were found in the region of Eric's stomach.

Fossils description

'Eric' is almost complete; most of the skull and skeleton have been found. 'Eric' is held by the Australian Museum, Sydney.

Evolutionary relationships

Plesiosauria (pliosaurs and plesiosaurs) were secondarily marine tetrapods that evolved from a group of terrestrial sauropterygian reptiles during the latest Triassic. Both pliosaurs and plesiosaurs survived until the Late Cretaceous, becoming extinct at the end of the era in the end-Cretaceous extinction event.

In a recent phylogenetic analysis, 'Eric' is placed as the most basal member of Rhomaleosauridae, within Pliosauroidea. The base of the rhomaleosaurid radiation occurred during the latest Triassic, and most of its members were Jurassic in age. This means that 'Eric's lineage was a long-surviving holdover from the Triassic, a phenomenon seen in many other Australian Cretaceous vertebrates (for instance, the Early Cretaceous Queensland dicynodont and Victorian labyrinthodont amphibian).


  • Kear, B. P. 2003. Cretaceous marine reptiles of Australia: a review of taxonomy and distribution. Cretaceous Research 24, 277-303.
  • Kear, B. P., Schroeder, N. I., Vickers-Rich, P, and Rich, T. H. 2006. Early Cretaceous high latitude marine reptile assemblages from southern Australia. Paludicola 5, 200-205.
  • Kear, B. P., Schroeder, N. I. And Lee, M. S. Y. 2006. An archaic crested plesiosaur in opal from the Lower Cretaceous high-latitude deposits of Australia. Biology Letters online. Doi:10.1098/rsbl.2006.0504 (1-11 + electronic supplementary material)
  • Molnar, R. E., 1991. Chapter 18: Fossil reptiles in Australia. Pp. 605-702 in Vickers-Rich, P., Monaghan, J. M., Baird, R. F. and Rich, T. H. (eds) Vertebrate Palaeontology of Australasia. Pioneer Design Studio, Melbourne.

Further reading

  • Long, J. A. et al. 2002. Dinosaurs of Australia and New Zealand and Other Animals of the Mesozoic Era. New South Wales University Press, Sydney.
  • Wallace, D. R. 2007. Neptune's Ark: from Ichthyosaurs to Orcas. University of California Press, Berkeley.