Leatherback turtle with partially eaten lion’s mane jellyfish.

Biologists dream in the superlative. Whales are the largest mammals, cheetahs are the fastest vertebrates, bar-headed geese fly the highest of any bird, and so forth. But you would be hard pressed to think of superlative features when it comes to turtles, or even reptiles. Rest assured there are superlatives in this order. Superlatives among reptiles are still with us.

Marine turtles, in some form, date from at least the Triassic period as early as 220 million years ago. For the next 100 million years, there was a rich diversity of other marine reptiles as well, but most of these were lost by the end of the Cretaceous period, 65 million years ago. Yet, marine turtles endured.

There was a monster sea turtle living during the Cretaceous period. Archelon and its few relatives ruled the sea as a 5 metre, 2500 kg behemoth turtle, but this animal became extinct shortly after the dinosaurs. But an intriguing and closely related shard of a family from this ancient …