Kronosaurus was a massive marine reptile called a pliosaur which lived in the waters around northeastern Australia during the middle Cretaceous Period circa 105-100 million years ago.
The fossils of this animal were discovered in 1899 in Queensland, Australia, consisting of the front of the upper and lower jaws. Although the fossils themselves were small, the implications were enormous, as the teeth were absolutely huge! Clearly, this fragment was merely the front tip of a massive skull possibly measuring 6 feet long or more. The teeth were identified as coming from a large pliosaur, the big-headed short-necked cousins of the plesiosaurs. In 1924, Albert H. Longman officially named this skull fragment Kronosaurus queenslandicus.
During the 1930s, Harvard University sent a paleontological expedition to Australia, and they returned with the partial remains of two more individuals. The university’s Museum of Comparative Zoology made a reconstruction of what the entire animal may have looked like, but much of this iconic and well-known skeletal mount was due just as much to interpretation as hard evidence. We now know that the museum’s staff made the skeleton much longer than it would have been by giving the animal too many vertebrae and ribs.
Largely due to the Museum of Comparative Zoology’s incorrect mounting, Kronosaurus was long-believed to have been the largest marine reptile ever. Books and magazines from throughout the second half of the 20th Century commonly stated that Kronosaurus measured 40 feet long or perhaps even longer. However, more recent studies have shown that these lengths were slightly exaggerated, and that the great beast actually measured 30-35 feet long – still impressive, no doubt, but just not quite as impressive as before. Moreover, gigantic ichthyosaurs from the Triassic Period such as Shonisaurus, Shastasaurus, and Ichthyotitan have challenged Kronosaurus’ title of “biggest marine reptile ever”. Unfortunately, we haven’t found a complete skeleton of a fully-grown Kronosaurus, so we don’t know for sure just how big the great behemoth got.
Kronosaurus queenslandicus. © Jason R. Abdale (July 7, 2025).
Kronosaurus’ fossils were found within the Toolebuc Formation, which, according to Benjamin P. Kear’s 2005 report, dates to the middle to late Albian Stage of the middle Cretaceous Period 105-100 MYA. Numerous fossils of fish and other marine reptiles have been found here, including the sea turtles Cratochelone and Bouliachelys, the ichthyosaur Platypterygius, and the plesiosaur Eromangasaurus. Fossils of pterosaurs and dinosaurs have been found here too, indicating that the rocks of the Toolebuc Formation were deposited along a coastal environment.
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Categories: Paleontology, Uncategorized
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