Fishes and sharks ENG

The shallow warm lakes covered a large part of the Krkonoše Piedmont Basin during Late Paleozoic. They were home to many species of fishes and sharks. Most of fishes were ray-finned with ganoid scales. These kinds of fish with cartilaginous skeleton had relatively robust bodies with an asymmetrical tail fin and thick shiny scales, commonly rhomboidal- or rectangular-shaped, serving especially as protection from bigger predators, since these fishes were only several dozen centimetres long. Their present-day relatives include for instance bowfins, sturgeons, and bichirs. Another type of fish were acanthodians, an extinct group of fish-like vertebrates. Its representatives looked like sharks, but their size ranged from 10 to 30 centimetres. Their body was covered with armour consisting of small thick scales; the head was protected with bony outer skin. The edges of fins were supported with firm spines – these are the most commonly found fossils. Acanthodians were active predators and were likely the first stage in development of more modern ray-finned fishes and sharks. The sharks were at the top of the food chain. Their characteristic features include a big mouth with triangular teeth, a distinctive dorsal fin spine behind the head, and a long dorsal fin stretching lengthwise across the body. The territory of the Geopark has yielded finds of several kinds of ganoid fishes of the artificial genus Amblypterus, several finds of acanthodians and sharks of genus Bohemiacanthus and Xenacanthus, especially around Semily, Košťálov, and Lomnice nad Popelkou.