Description

Stenopterygius sp.
Early Jurassic
Posidonia Shale – Lias Epsilon
Holzmaden, Germany

27 inch ichthyosaur on 31 inch slab from the famous Holzmaden quarries.

Ichthyosaurs are iconic marine reptiles of the Mesozoic era. Just as dolphins descended from land mammals that adapted to live in the sea, the ancestors of ichthyosaurs were reptiles that lived on land and were contemporaneous with the dinosaurs. The limbs of ichthyosaurs are characterized by a considerable reduction in the size of the long bones and a very high number of phalanges. The result is a highly flexible fin. The propulsive tail fin of dolphins and ichthyosaurs have the same adaptations, dolphins having a horizontally oriented tail, ichthyosaurs a vertical one. Many other details of ichthyosaur anatomy reveal their extensive adaptation to aquatic life. Most fast-swimming animals have a fusiform body shape, thus ichthyosaurs, dolphins, and sharks all evolved to deal with the same environmental pressures of high speed propulsion in the ocean and developed similar adaptations as a result. Their amazing similarity is a classic example of convergent evolution as a response to similar adaptive pressures. This very example is frequently cited in textbooks.

The Stenopterygius specimen here comes from the world famous Holzmaden Quarries near Stuttgart, Germany which have produced extraordinary fossil specimens since at least 1598. In the 18th century, Holzmaden ichthyosaurs were discovered with deposits of carbon surrounding their bones. This carbon was actually the
remains of the animal’s soft tissues and was a first for this kind of preservation known. In the case of the ichthyosaurs, the carbon deposits showed that the body outline of the creature is almost dolphin-like, which was previously completely unknown.