The hidden date for this stamp can be found along the right edge of the stamp.
It seems people everywhere are re-discovering a fascination with the "Age of Reptiles", a period in which the dinosaur was the dominant land creature. Canada Post Corporation is contributing to this phenomena with its issue of four stamps featuring three dinosaurs and one marine reptile to launch Stamp Month on October 1, 1993. The dinosaurs had 165 million years of domination of the earth from approximately 230 million to 65 million years ago. One theory of why the great beasts became extinct is because they could not adjust to drastic climatic changes brought about by a giant asteroid striking the Earth. Remains of dinosaurs have been found on all continents, with the first Canadian discovery being made at Morgan Creek, Saskatchewan in 1874 by geologists of Her Majesty's North American Boundary Commission. The famous "badlands" of Alberta yielded the most dinosaur finds in Canada to date. This was a six-meter long Cretaceous-period marine reptile which represents something of a cross between a lizard and a seal. The most common of the mosasaurs, the Platecarpus descended from land lizards and had limbs that were modified into paddle-like flippers, with a vertically expanded, eel-like tail. Savage and pugnacious in nature, they fed on fish and were in turn attacked by sharks. Platecarpus inhabited the North American mid-continental seaway, which 85 million years ago extended from Texas to the Arctic Ocean. In Canada, remains of Platecarpus have been discovered in the District of Mackenzie, Northwest Territories and near Morden, Manitoba. They have also been identified from Alabama to Europe to southern Africa. The group to which it belonged, mosasaurus, became extinct at the about same time as dinosaurs vanished from the face of the Earth. Rolf Harder has designed all three stamps sets in the "Prehistoric Life in Canada" series. The choice of subjects was made on the advice of Canadian paleontologists and reflects importance, location in Canada, and visual suitability for depiction on stamps. A key element in the design is the rendition of the texture of the creature's surface, which is produced by a mezzotint stipple effect. Although the colour of these beasts is subject to speculation, each is shown of a hue appropriate to its surroundings.