File:Stenopterygius quadriscissus (fossil ichthyosaurs) (Posidonia Shale, Lower Jurassic; Holzmaden area, Germany) (35788640735).jpg

Stenopterygius quadriscissus (Quenstedt, 1858) - fossil ichthyosaur skeletons from the Jurassic of Germany. (CM 876, CM 6001, CM 6003, Carnegie Museum of Natural History, Pittsburgh, Pennsylvania, USA)

Ichthyosaurs are an extinct group of large, predatory, marine reptiles. They had a fusiform body similar in gross morphology to modern dolphins and porpoises. The latter are mammals, while ichthyosaurs were reptiles. The evolution of similar body plans in unrelated organisms is called convergent evolution. Ichthyosaurs and dolphins are the most commonly cited examples of this evolutionary process.

Ichthyosaur fossils are only found in Mesozoic sedimentary rocks - they first appear in the Triassic and go extinct in the Cretaceous.

The specimens shown above are from the famous Holzmaden Lagerstätte, a Jurassic-aged soft-bodied fossil deposit in Germany. The deposit consists of marine black shales and has produced many complete vertebrate skeletons, many of which have a carbonized halo/outline of skin. The latter is seen in sharks, bony fish, crocodilians, pterosaurs, plesiosaurs, and ichthyosaurs. Many female ichthyosaurs are fossilized with embryos in their bodies, or in the apparent act of giving birth. An alternative interpretation of the latter is that such fossils represent post-mortem abortions due to compression from burial in sediments. The Holzmaden deposit also has fossil logs with encrusting crinoids, plus ammonites & belemnites (both cephalopods) with soft tissues preserved - including ink sacs, tentacles, and hooks.

From museum signage: When different types of organisms adapt to similar environments or lifestyles, they often evolve comparable features. This phenomenon is known as convergent evolution.

Ichthyosaurs ("fish lizards") were reptiles. Nonetheless, their long jaws filled with pointed teeth, streamlined, muscular bodies, and paddle-like limbs were very much like those of modern marine mammals such as dolphins and porpoises.

Most ichthyosaurs probably also had habits comparable to dolphins and porpoises. They lived in the ocean, ate fish and squid, could not walk on land, and had to come to the surface to breathe. Some ichthyosaur skeletons also preserve remains of unborn babies inside. This indicates that, like today's marine mammals (but unlike most living reptiles), ichthyosaurs bore their young alive and in the water.

Among the more than 3,000 ichthyosaur specimens collected from Holzmaden so far, the dolphin-sized Stenopterygius is by far the most common. Much of our knowledge of ichthyosaur biology comes from scientific studies of this species. One of the smaller skeletons shown here preserves the outline of the body in exquisite detail, while the largest contains remains of invertebrate animals within its abdomen - perhaps its last meal.

Classification: Animalia, Chordata, Vertebrata, Reptilia, Ichthyosauria, Ichthyosauridae

Stratigraphy: Holzmaden Lagerstätte, Posidonia Shale, Toarcian Stage, upper Lower Jurassic

Locality: unrecorded/undisclosed site at or near the town of Holzmaden, southwestern Germany

See info. at: <a href="https://en.wikipedia.org/wiki/Stenopterygius" rel="nofollow">en.wikipedia.org/wiki/Stenopterygius</a> and