Species: Kronosaurus queenslandicus (type species) and Kronosaurus boyacensis (older species), along with a similar but older and likely closely related brachauchenine called Sachicasaurus vitae.

Classification: sauropterygian-plesiosaur-pliosaur-brachauchenine

Fossil range: late Aptian-mid Albian (116-105 mya)

S. vitae is known from the lower Arcillolitas Abigarradas Member of the Paja Formation (Barremian, 130-125 mya)

K. boyacensis is known from the upper Arcillolitas Abigarradas Member of the Paja Formation (late Aptian, 116-113 mya)

Kronosaurus sp. fossils have been documented from the Wallumbilla Formation (late Aptian, 116-113 mya)

K. queenslandicus is recorded from the Toolebuc Formation (110-105 mya)

Geographic range: K. queenslandicus hails from Queensland, but K. boyacensis comes from Colombia

Size: 9-11 meters in length and up to 10 tons for all species, making them the likeliest contenders for the title of largest known pliosaurs.

Kronosaurus queenslandicus was the pliosaur that made these predatory marine reptiles famous (before being derailed in 1999 by an infamously oversized Liopleurodon), but its also another icon of Cretaceous Australia, as the genus originated in Australias Toolebuc Formation. First described from teeth in 1924, subsequently a partial skull was found in 1229. But Kronosaurus first rose to fame when the Harvard Museum of Comparative Zoology sent an expedition to Australia to procure Australian mammals in the 1930s, but by chance, one member of the team found something far more extraordinary at Toolebuc and uncovered a much more complete skeleton of this Cretaceous behemoth. It took some 20 years to recover the entire skeleton and in 1959, a full-body reconstruction was mounted and put on display at the Harvard. Instant sea monster icon.

This put Kronosaurus in the limelight, with its massive 2.7-meter head and a body stretching 13 meters in length in total, and the Harvard specimen was quickly dubbed the biggest and fiercest sea monster ever to have swam our oceans, and it was widely speculated that the animal could have attained a max length of 15 meters or more. However, the Harvard specimen was later shown to have been reconstructed with too many vertebrae, and subsequent workers have downsized it to a length of 9-11 meters. But that still makes Kronosaurus queenslandicus one of the largest known raptorial marine reptiles on record.

Meanwhile in Colombia, another, very similar pliosaur was found in the Paja Formation in 1977, also in the form of a nearly complete skeleton and was later erected as Kronosaurus boyacensis. This further cements Kronosaurus as the most important pliosaur genus, as both species are known from remarkably complete remains, which is quite the opposite for most other taxa, except for one specimen of Liopleurodon ferox. Sachicasaurus vitae (named in 2019) follows this trend by also preserving a remarkably complete skeleton. Brachauchenines are undoubtably the holy grail for pliosaur researches.

Toolebuc is an important fossil site for understanding the marine life of the Cretaceous, as that place not only housed Kronosaurus, but also the ichthyosaur Platypterygius, the long-necked plesiosaur Eromangasaurus (theres also Woolungasaurus, known from Wallumbilla) and the giant sea turtle Cratochelone, as well as the ornithocheirids known as Mythunga and Aussiedraco. I would have gone with that setting for my Updated with Dinosaur and only vetoed the idea because it was too close in time to Giant of the Skies and disrupted the original flow of the episodes and created a shortage of Jurassic settings. Well, that and sea crocodiles.

https://www.deviantart.com/wdghk/art/Aussie-Plesiosaur-Kronosaurus-queenslandicus-875640824