Giant Ichthyosaur Ichthyoтιтan severnensis Nears Blue Whale Size — While Pliosaurs Like the Dorset “Sea Rex” Ruled as 12-Metre Apex Killers

The Late Triᴀssic oceans hosted some of the largest marine reptiles ever — including Ichthyoтιтan severnensis, a shastasaurid ichthyosaur whose jawbone fragments suggest a body length of ~25 metres, approaching the size of the largest blue whales. Meanwhile, colossal pliosaurs such as the recently excavated 2-metre-skulled specimen from England’s Jurᴀssic Coast reached 10–12 metres and dominated as hypercarnivorous macropredators.

Described in 2024 in PLOS ONE by Dean Lomax and colleagues, Ichthyoтιтan is known from two mᴀssive surangular bones recovered from the UK’s Westbury Mudstone Formation (~202 million years ago). Scaling from the 21-metre Shonisaurus sikanniensis indicates a length of 22–26 metres — making it the largest marine reptile currently known. These filter-feeding giants cruised Triᴀssic seas alongside smaller marine reptiles, using their enormous size to dominate the food chain.

In contrast, the 2.1-metre pliosaur skull (“Sea Rex II”) extracted from Kimmeridge Bay in 2024 belongs to a ~12-metre predator with a bite force exceeding 20,000 newtons. Published in Cretaceous Research (2026), this Kimmeridgian specimen reveals a short-necked, four-flippered hunter capable of taking down other marine reptiles.

While no pliosaur exceeded blue-whale proportions, Ichthyoтιтan demonstrates that ichthyosaurs independently approached the absolute upper size limit for marine vertebrates during the Triᴀssic — a remarkable case of convergent gigantism with modern baleen whales. Both groups vanished by the end of the Cretaceous, leaving blue whales as the undisputed champions of marine gigantism today.