Temnodontosaurus and the Soft Tissue of the “Dinosaur-like” Marine Mammal: They Swim Like Modern Sharks!

In May 2024, a groundbreaking study published in Nature revealed long-held secrets about how ichthyosaurs—a group of “dinosaur-era marine mammals”—swam. Specifically, a remarkably well-preserved specimen of Temnodontosaurus (a giant Early Jurᴀssic ichthyosaur, ~200–180 million years ago) in Germany revealed nearly perfect soft tissue, showing they swam in a thunniform motion—identical to large sharks and modern tuna.

Temnodontosaurus was a large ichthyosaur (9–12 meters long) with a long head, sharp teeth, and a slender body. Previously, it was thought that ichthyosaurs swam by undulating their entire bodies like eels. But the new specimen from Holzmaden (Germany) has completely changed that:

• The dorsal and caudal fins are perfectly preserved with their collagen fiber structure. The skin had melanosomes (pigment cells), resulting in darker coloration on the back and lighter coloration on the belly—a form of countershading similar to sharks.
• The body was elongated, the tail was a powerful sickle shape, and the pectoral/tail fins were designed to generate strong propulsion at the rear of the body.
• The study concluded that Temnodontosaurus (and many post-Triᴀssic ichthyosaurs) swam by vigorously flapping their tails like great white sharks or tuna, rather than bending their entire bodies. This highly efficient swimming style allowed for rapid and energy-efficient movement over long distances—suitable for their role as “super predators” of the Jurᴀssic ocean.

This finding also shows a strong evolutionary convergence between ichthyosaurs and modern sharks: both developed a streamlined body shape, sickle-shaped tail fins, and a thunniform swimming style to dominate the open sea environment.

As of June 2026, the Temnodontosaurus specimen with soft tissue remains one of the most important discoveries regarding the functional biology of ichthyosaurs. It demonstrates that these “sea mammals of the dinosaur era” not only looked like sharks but also swam like sharks—a classic example of evolutionary convergence between two completely different groups of animals.

The Jurᴀssic oceans once had their own “sharks”—and Temnodontosaurus was one of the most fearsome rulers.