Queensland is home to the world’s largest marine reptile, the Estuarine or Saltwater Crocodile, also known as the Indo-Pacific Crocodile. Male “Salties” may grow over 6 metres in length and weigh over 1,300 kilograms. Recently an Indo-Pacific crocodile measuring 6.4 metres and weighing 1075 kilograms was captured in the Philippines. It is thought that even larger specimens may exist.

In the modern world, Saltwater Crocodiles are apex predators, however they would only be considered minor predators if they lived among the array of large carnivorous marine reptiles which hunted the inland seas of Queensland during the early Cretaceous Period.

At this time, there was a great inland sea which stretched from South Australia into northern NSW and southern and central Queensland. We know about the marine life of this region because the bones of many sea creatures fell to the sea floor, where they eventually became fossilised and formed layers of what was to become the Great Artesian Basin.

The ancient marine reptiles evolved from land animals that returned to the sea as they developed the ability to swim. The reptiles retained lungs and had to surface to breathe air and over millions of years evolved a variety of body shapes, swimming and hunting techniques. The major types of ancient marine reptiles in Queensland were:

Turtles – were the most common marine reptile in the inland sea. There were a number of species which resembled modern green turtles. An extinct giant sea turtle, Cratochelone, was thought to be 4 metres long; however this estimate is based on incomplete fossil records.
 
Ichthyosaurs - or “fish lizards” were quick, agile swimmers, with a streamlined shape that resembled dolphins. They used the same swimming technique as fish; they powered forward by moving their tail laterally and steered with fin like paddles. Young were born alive at sea, ready to swim from birth. Large ichthyosaurs such as Platypterygius grew to 7 metres.

Plesiosaurs - these sleek animals swam with their paddles and steered with their tail and head. They had four paddles, long necks, fine teeth and small heads. It is likely that they fed on fish, squid, bivalves and small prey. It is believed that they may have left the water to lay their eggs on land.

Pliosaurs – used the same swimming techniques as the plesiosaurs but had a different body shape, usually big heads and short necks. They were probably fierce opportunistic predators that hunted fish, giant squid and other marine reptiles. The largest was Kronosaurus queenslandicus, a skeleton of this species was 12.5 metres in length, 1.5 metres in diameter and had 15 cm teeth, some Kronosaurus teeth measuring 30 cm have also been found. This species had four incredibly strong paddles which were able to push its streamlined body through the water at high speed in a straight line.