Ichthyosaurs might have a Permian origin

I just read a short note, Earliest Triassic ichthyosaur fossils push back oceanic reptile origins, from Current Biology 33:159-179, March 2023, Benjamin Kear, Victoria Engelschion, Oyvind Hammer, Aubrey Roberts, Jorn Hurum.

As I understand this note, some very early Triassic ichthyosaur vertebrae are cancellous or spongy, which hypothetically held oil as a buoyancy mechanism. Modern whales also have cancellous bones containing oil. A blue whale’s skeleton (died 1998 due to collision with boat) is still dripping oil today.

Nice convergent evolution, but there’s another implication.

Cancellous bone is an adaptation to an entirely pelagic lifestyle, so early Triassic ichthyosaurs were living out in the open ocean all the time. The 2 million years or so between the end-Permian extinction and these fossils isn’t enough time for all the adaptations (flippers, smooth skin, live birth, cancellous bone, etc) necessary for an open ocean life to have evolved. Therefore, ichthyosaurs evolved in the Permian, and survived the Great Dying.

That’s an interesting thing to imply. Current orthodoxy is that ichthyosaurs evolved after the end-Permian extinction, radiating rapidly due to vacant ecological niches, and growing to large sizes because ammonoids recovered rapidly after the extinction and had virtually no other predators.

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I tried, but failed, to find out if plesiosaurs or thalattosuchians had cancellous bone.