What is specific "mammalian" about our eyes ? Are our eyes the best eyes ever developed by evolution ? Are some design constraints derived from evolutionary heritage ?
				To Outline of Lecture "On the Biology of Seeing Colors"
		Recent studies (using behaviour testing, electrophysiology, morphology, and molecular biology) are digging up a wealth of new information about the visual system of man and its relatives. By combining some recent findings the following page suggests a possible scenario for the specificities and the evolution of our visual system.

1) A very short outline of the evolution of mammals

with special attention to the visual system.

At one stage of evolution (the Permian) the reptiles represented the largest forms of animal life on earth. They diversified to plant eaters or meat eaters and some managed swimming and flying. The most famous group are of course the dinosaurs, including the bi-pedal Tyrannosaurus.

Later most reptilian groups became extinct but some groups survived. Today these lizards, turtles snakes and crocodiles or the Tuatara (left) again face a big threat of extinction: from the expansion of the human species.

Around 250 Mio years ago there was a branch from another reptilian group - the Synapsids. They had evolved some different features. These "Cynodonts" (see a 3D-skull ?) remained on the ground with all four legs but changed their skeletons for faster running and their teeth became more specialized to do different jobs. Some were consequently called "Weasel lizards". Probably they were already covered by some fur.

From this Synapsid animals the first mammalian creatures evolved and coexisted with their big reptilian "cousins". They were not very impressive when compared to the dinosaurs or to their big future descendants. They resembled big shrews, probably eating insects, worms etc., some perhaps also eggs of dinosaurs.

These creatures such as Megazostrodon ..evolved further by becoming even smaller, increasing the brain, developing milk gland. During the Jurassic ages the Pantotheres ..definitely abandonend egg laying, by shifting their arms close under the ribs they became better runners and climbers. This animals(50 Mio yrs later) became larger again and are considered as the ancestors of modern placental mammals.

Today the mammals (besides birds) represent the most visible part of the animal kingdom. Because of temporary isolation and splitting of the old Southern continent Gondwana during recent earth history, two of the surviving mammalian groups - the egg laying Monotremes (Echidna and Platypus) and the Marsupials (e.g. Kangaroos and Opossums) - persisted in Australia and South America. In most Northern regions however the Placental type of mammals diversified and adapted to all biotopes and lifestyles (including to life in the oceans). Even by just looking at the animals above we see that a considerable change took place along the evolution from reptilian to mammalian life forms. The change of body shape indicates that the first small mammals also evolved some new functional features.

Next page: 2) Characteristics of Reptilian Photoreceptors