Ichthyosaurs

Ichthyosaurs were a group of marine reptiles that thrived during the Mesozoic era, spanning from the Triassic to the Cretaceous period. They exhibited remarkable adaptations to the aquatic environment, boasting a hydrodynamic body shape akin to sharks or dolphins. Their tail was inverted heterocercal, meaning the vertebral column extended into the lower part of the caudal fin. Their skin was smooth, and they possessed elongated skulls adorned with large to enormous eyes. Their mouths were equipped with numerous teeth, which varied in size among different species – some ichthyosaurs had small teeth, others had large ones, and some had none at all.
The scapular and pelvic girdles of ichthyosaurs were notably small or even absent, and their limbs featured hyperphalangia, meaning they had a large number of phalanges for each finger. In some genera, they even displayed hyperdactyly, possessing more than five fingers. Their musculature was specialized for snapping, and they propelled themselves through the water by undulating their tails sideways. Their fin-like limbs aided in changing direction and stabilizing their movement. Most ichthyosaurs were predators, preying on fish, molluscs (especially cephalopods), arthropods, and even smaller marine reptiles, including other ichthyosaurs. Fossilised stomach contents of some ichthyosaurs have revealed the presence of stones (gastrolites), which likely aided in digestion. Fully adapted to marine life, ichthyosaurs never ventured onto land. Instead, they gave birth to live young that developed within their mother’s body. This reproductive strategy is supported by fossil evidence, such as the discovery of fossilized ichthyosaur females alongside newly born offspring or embryos inside the mother’s body. While the average length of ichthyosaurs was around 2 meters, larger forms also existed.