The name Ichthyosauria comes from Greek and means “fish lizard”. The name is made up of two parts: Ichthys, meaning fish, and sauros, the lizard. The taxon Ichthyopterygia was established in 1840 by the English biologist and paleontologist Sir Richard Owen.
Ichthyosaurs are a group of extinct reptiles that descended from land lizards and later became water-dwelling, marine organisms. Over time, their extremities developed into impressive fins. The body is streamlined and shows a strong convergence with the bodies of sharks and dolphins. Over time, approximately eighty species have been scientifically described. In 1811, Mary Anning, then twelve years old, found the first complete skeleton of an Ichthyosaurus, the eponymous genus of this group, in Lyme Regis (England).
At this point in time, finds of Ornithischia and Saurischia (Dinosauria) were still completely unknown. Finds of ichthyosaurs initially puzzled the scientific world because many features of these fossil organisms were reminiscent of land vertebrates. Some researchers saw them as fish, others viewed them as amphibians or even classified them as marine mammals.
Evolution: The first ichthyosaurs appeared around 251 million years ago in the Lower Triassic (Olenekinian). These creatures still had an elongated, lizard-shaped habit and probably moved in the shallow water near the coast by wriggling their entire bodies. At the end of the Middle Triassic, the elongated ichthyosaurs disappeared and were replaced in the Upper Triassic by forms with a more spindle or torpedo-shaped body. At that time, these ichthyosaurs also conquered the open ocean habitat (McGOWAN & MOTANI, 2003). In the Middle Triassic, the ichthyosaurs showed their greatest diversity of forms.
The ichthyosaur Cymbospondylus youngorum from Nevada was 17 meters long, weighed 45 tons and was the first giant creature to ever live on Earth. It probably took "only" about three million years from the first appearance of ichthyosaurs until they reached this body size around 246 million years ago (in the Middle Triassic).
Even though the ichthyosaur is the size of a sperm whale, the two have little in common, not even the evolutionary speed of their body growth.
"The evolutionary models show very clearly that ichthyosaurs had an initial size boom and became giants early in their evolutionary history, while whales took much longer to reach their maximum size."
In the Lower Jurassic (Black Jurassic, Lias Epsilon) the ichthyosaurs had their greatest diversity, and deep-diving species emerged. Several species or subspecies are known from the genus Stenopterygius alone. Particularly rich finds from this period are the Posidonia slate (Lias Epsilon) from Bad Boll, Ohmden and Holzmaden (near Stuttgart) in southern Germany. Over the course of many decades, these dark slates yielded approximately 3,000 specimens of the genera Stenopterygius, Eurhinosaurus and Temnodontosaurus. Stenopterygius is the most common genus of ichthyosaurs in the Holzmaden Posidonian Slate. Type specimens of the genus Ichthyosaurus were found in England. In the Cenomanian period, the ichthyosaurs died out around 94 million years ago.
Stenopterygius belongs to the group of advanced ichthyosaurs. Similar to modern tuna, it probably had a fairly stiff skeleton. It can also be assumed that he was a very good and fast swimmer simply by the movement of his fins. The streamlined body had a vertical tail fin. Additional, paddle-shaped front and hind fins, which have finger and toe phalanges, were primarily used for control. Like other reptiles, ichthyosaurs breathed through their lungs, so they had to surface from time to time - like today's whales - to take a breath.
The first exposure of a Stenopterygius with skin preservation by Bernhard Hauff in 1892 was sensational and initially controversial. Fatty proteins can be detected using modern methods.
The diet of ichthyosaurs can be described as carnivorous (mainly cephalopods) and has come down to us from the well-preserved remains of prey in the stomach region. Belemnite parts and fish scales as well as other vertebrate remains were found as stomach contents.
Ichthyosaurs developed very specialized teeth. In addition to purely fish-eating forms, there were also representatives with teeth for cracking hard-shelled food such as mussels, snails, ammonites, brachiopods, etc.
Ichthyosaurs were land vertebrates. They have secondarily switched back to life in the water. They were so adapted to life in the sea that they could no longer go on land to lay their eggs and gave birth to live young.
The shoulder girdle is not firmly attached to the skull as in fishes, and in their fins the upper and lower arm bones, carpal bones and finger bones can be distinguished.
A particularly characteristic feature of ichthyosaurs is the scleral ring, which is located in the outer skin of the eye and around the iris.
The scleral ring is a ring-shaped, bony reinforcement of the eye; it is also found in birds, the extinct dinosaurs, pterosaurs, and also some modern reptiles such as iguanas.
The scleral ring probably served to keep the ichthyosaurs' flat, non-round eyeballs in shape because their large eyes were exposed to varying water pressure while swimming. The part of the eyes closer to the snout was exposed to greater water pressure than the part further back.
The largest eye found in an ichthyosaur is also the largest eye of all vertebrates. It was 26.4 cm in diameter and belonged to Temnodontosaurus platyodon. The eyes were very bright and enabled hunting at great depths.
The scleral ring symbolizes the Posidonia slate from Holzmaden, which is why it was chosen as the logo for Fossiland.
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