What was the largest pliosaur?
I'm working on a learning fair project with my son titled "Giant Predators of the Ancient Seas". We are having trouble finding a definitive answer to the question of the which pliosaur was the largest. Resources tend to name either Liopleurodon or Kronosaurus. Please let us know what the current thinking on the matter is.?

The identity of the largest pliosaur has been a matter for some debate recently, and most popular books are quite simply wrong. I think it comes from the BBC series, 'Walking with Dinosaurs', which featured 'Liopleurodon' as a 25m, 150 ton monster. Other researchers for popular books have taken these numbers at face value, and changed them slightly to make it look as if they've done their own research (they make it 23 or 24 m long, rather than 25).

I've worked with a number of specimens of Liopleurodon, and it was not 25 meters long. At the most, it was around 10m, weighing around 4 tons - a formidable predator, but not baleen whale size. However, there are a few odd bones which show that there was another, much larger predator around at the same time. All we have are a couple of teeth about 400mm long (the largest liopleurodon teeth measure about 200mm from root to tip - much the size of T-rex teeth), three vertebrae the diameter of dinner plates - well over twice the diameter of those of Liopleurodon, and 40% bigger than those of Kronosaurus. There is also a lower jaw in Oxford Museum which is over 3m long, and about 10 million years younger than Liopleurodon. The skull of Liopleurodon is about one seventh of its' overall length, which would make this animal 21 meters long, weighing around 20 tons - around the size of a Sperm Whale, the largest modern carnivore.

The problem with these few enormous bones is that we don't have enough material, or material of the right kind, to work out if they came from a new species of mega-predator, or from a very large individual of a known species. The jury is still out, and every time I go down one of the clay pits, I hope.

Kronosaurus was a very large animal, though not as large as this British pliosaur. It is well known from the skeleton in Harvard Museum of Natural History. Unfortunately, this specimen is largely reconstructed from fragmentary material, and is much longer than more recent finds have shown the animal to have been. One of the best preserved comes form Columbia, and shows that it was a strange beast, with a huge head about one quarter of its' overall length.

When talking about marine monsters, I have to mention the latest and most extraordinary find of all, a giant ichthyosaur from British Columbia, Canada. This monster is 23 meters long, and is a complete, articulated skeleton. The skull alone is 5.5 meters long. We don't know much about it yet. It is being excavated bit by bit, but as it is in a very remote place all the bones have to be taken out by helicopter. The block containing half the skull weighed 3 tons!

Hope this helps your son with his science project