Recent Items – 1999
July 15, 1999
[Several examples of ichthyosaur fossils have been found in the Peace region. This article gives some technical information about these aquatic giants]
While dinosaurs ruled the land, the ichthyosaurs shared the seas of the world with the other great groups of large marine reptiles, the plesiosaurs and mosasaurs.
“Ichthyosaur” means “fish lizard.”
The earliest ichthyosaurs had long, flexible bodies and probably swam by undulating, like living eels. More advanced ichthyosaurs had compact, very fishlike bodies with crescent-shaped tails. The shape of these ichthyosaurs is like that of living tunas and mackerels, which are the fastest fish in the ocean; like them, the later ichthyosaurs were built for speed.
Rare fossils have been found that show ichthyosaurs actually giving birth to live, well-developed young; ichthyosaurs never had to leave the water to lay eggs. In fact, from their streamlined, fishlike bodies, it seems almost certain that ichthyosaurs could not leave the water. Yet they still breathed air and lacked gills, like modern whales.
Ichthyosaurs were not dinosaurs, but represent a separate group of marine vertebrates. Because ichthyosaurs were so specialized and modified for life in the ocean, we don’t really know which group of vertebrates were their closest relatives. They might have been an offshoot of the diapsids — the great vertebrate group that includes the dinosaurs and birds, the pterosaurs, the lizards and snakes, and many other vertebrates. On the other hand, some have suggested that the ichthyosaurs were descended from a distant relative of the turtles.
The first ichthyosaurs appeared in the Triassic. In the Jurassic, ichthyosaurs reached their highest diversity, and then began to decline. The last ichthyosaurs disappeared in the Cretaceous — several million years before the last dinosaurs died out. Whatever caused the extinction of the dinosaurs did not cause the ichthyosaurs to die out.
Ichthyosaurs diversified very quickly once they appeared. Several different body plans appeared in the Early and Middle Triassic. Shonisaurus popularis and probably Himalayasaurus tibetensis (both Late Triassic), reaching 15 metres, are the largest ichthyosaurs that have been described, but there are undescribed specimens that are larger. Among the smallest ichthyosaurs is Chaohusaurus geishanensis (Early Triassic), which probably did not reach 70 cm.