Large extinct sea reptiles known as ichthyosaurs were common during much of the Mesozoic epoch. They originally appeared about 250 million years ago (Ma), and one species of the Ichthyosauria order persisted into the Late Cretaceous period some 90 million years later.
It was once thought that ichthyosaurs and other ichthyosauromorphs descended from an unnamed group of land reptiles during the Early Triassic period. These early amphibious reptiles improved their swimming abilities over time and finally transformed their limbs into flippers. They began to give birth to live young and changed their body shape to resemble a fish, breaking their last connection to the Earth.
A 2014 expedition to western Spitsbergen’s Ice Fjord collected a significant amount of concretions, which were then brought to the Natural History Museum at the University of Oslo for additional research. Limey sediments that accumulated over decaying animal remains on the old seabed gave rise to concretions.
In concretion deposits thought to be too old for ichthyosaurs to have existed, researchers discovered bony fish, strange “crocodile-like” amphibian bones, 11 articulated tail vertebrae from an ichthyosaur, and other unusual fossils.