Palaeontology and taphonomical studies of osteichthyes in limestones in Bueng Sam pan, Changwat Phetchabun, Northeast Thailand

Abstract

Limestones in Amphoe Bueng Samphan, Phetchabun, contain not only abundant coral building animals, Brachiopods, Mollusca, Rugosa, Ammonoids, Calcareous sponges and Bryozoans, but fish fossils. The discovery was in the course of field work II. First of all, I prepared the geologic map and classified geomorphic surfaces in study area scaled 25,000 and determined stratigraphical position of fish fossil localities. And after that, by using lithology and sedimentary structures in limestone. paleoenvironments are reconstructed. Fish fossils are two horizons. The first one is the same locality with Crinoid limestone (Horizon 1). The color of this limestone is reddish purple and orients to the layer parallel to bedding plane. The other one is in the alternation of limestone (100-200 cm.) with black shale (10-20 cm.). This limestone has laminated partly, on the upper surface, trace fossil of creeping animal are observed. Expected microenvironments are lagoonal swamp with some times invasion of fresh water. This groups originated from fresh water environments. So, according to explosive evolutional trend, they may extend to marine environments. It is important to collect more samples and precise taxonomy. Fish fossils are mostly the surface of body, hard diamond scales. They are lacking the skull, according to the characteristics of fish scale, fish fossils are belonged to Osteichthyes ( Class ), Chondrostei ( Superorder ), Palaeochondrostei ( Superorder ), Paleonisciforms ( Order ). These group is characterized by the characteristic “Ganoid” scale. Like these fish fossil had been refered from China (Lu and Ma,1973)