The Triassic predator that hunted like a seal but paved the way for plesiosaurs

Nature · Published 3 October 2026 Swipe more like this →

In short: Long before the ocean giants of the Jurassic, the Nothosaurus prowled the Tethys Sea. This semi-oceanic reptile, with its needle-toothed jaws and webbed limbs, lived much like a modern seal. It was a pivotal evolutionary link, bridging the gap between terrestrial ancestors and the massive, fully aquatic predators that followed.

Thriving between 245 and 228 million years ago, Nothosaurus was a widespread genus of sauropterygian reptile. Its fossils have been recovered across a vast range, from North Africa and Europe to China. While the typical Nothosaurus reached about 4 metres in length, larger species like N. giganteus and N. zhangi could grow up to 7 metres, making them formidable hunters in the Triassic seas.

The creature’s anatomy reveals a fascinating, if imperfect, transition to aquatic life. It possessed a broad, flat skull lined with sharp, needle-like teeth, ideal for snatching fish and other marine prey. Evidence from trackways discovered in Yunnan, China, in 2014 suggests these animals used their webbed paddles to churn up the seabed, exposing hidden creatures. Unlike the later, highly specialized plesiosaurs, Nothosaurus remained semi-oceanic, using a combination of tail undulation and limb-driven swimming to navigate the water.

Beyond its hunting habits, Nothosaurus displayed remarkable developmental plasticity. Research on a sample of twenty-four specimens revealed that seven showed evidence of vivipary, or live birth. This reproductive strategy may have been an evolutionary adaptation to ensure higher survival rates for offspring in a high-mortality environment. While phylogenetic studies, such as those by Liu et al. in 2014, have complicated the classification of the genus—leading to the reassignment of species like N. juvenilis to Lariosaurus—the Nothosaurus remains a critical subject for understanding the evolution of marine reptiles. It is widely believed that one branch of these nothosaurs eventually gave rise to the pliosaurs and plesiosaurs that would dominate the oceans for millions of years to come.

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