14 DAY TRIAL // Ichthyosaurs (ichthyosaur literally means "fish lizard" in Ancient Greek) were marine reptiles from Mesozoic (Dinosaur Era).
First records are from about 250 million years ago, earlier than dinosaurs, and disappeared during the Lower Cretaceous, before the extinction of the dinosaurs (which vanished at the end of the Cretaceous).
Primitive Ichthyosaurs had serpentine (snake like) bodies, but gradually they got a fish like appearance. The most evolved species looked like hunchbacked dolphins, and even had dorsal fins. They were the size of modern dolphins and probably played the same role, but some species reached 40 feet (14 m). Their body shape indicated they were fast swimmers, but until a recent discovery it was not known in which way their fins got rigid for swimming.
Current fast swimmers like tuna, dolphins and sharks have stiff fins and a streamlined body shape. Fast swimming sharks - like the great white shark - have in the skin structure collagen sheets that lie at slightly different angles to one another. The collagen envelope is thicker around the tail and dorsal fins in order to stiffen them. "We showed that the support given by collagen in sharks is every bit, if not stronger, than bone," Lingham-Soliar said.
"The dorsal fin and tail flukes of dolphins are similarly stiffened with collagen, but the fibers are arranged more randomly than in sharks," said Theagarten Lingham-Soliar of the University of KwaZulu-Natal in South Africa.
"A large and stiff back fin deflects a large body of water effectively and pushes an animal through the water," Lingham-Soliar explained.
Tuna's dorsal and tail fins are stiffened by bony spines, like in every bony fish. When Lingham-Soliar and Gerhard Plodowski of the Senckenberg Research Institute in Germany examined fossilized soft-tissue from a well-preserved specimen of an Ichthyosaurs species called Stenopterygius quadricissus(image), they found an arrangement identical to that found in the great white shark's fins. Layered sheets of collagen fibers were found in the skin of the dorsal and tail fins.
This is an example of convergent evolution, in which animals not closely related develop similar characteristics. The assembly tuna - shark - ichthyosaur - dolphin was already an example of classical convergent evolution of body morphology. Now we talk about an anatomical convergence. The new study has confirmed what scientists have long suspected. "Collagen is one of the most effective materials for toughening something, so from that point of view, it's not a surprise" Lingham-Soliar told.
"Where one is surprised is to find good soft tissue in an animal that is so, so very old-200 million years old-and to actually find the collagen fibers in the [fin] structures. That becomes near miraculous."
Present in animal bone and connective tissues, collagen is a fibrous protein present in bone and connective tissues. It gives skin its elasticity, and its degradation with age causes wrinkles. The collagen would have stiffened the fins, allowing the reptiles to move through water like torpedoes.