PALEONTOLOGY OF PROBOSCIDEAN FOSSILS FROM THAISIN SANDPIT, AMPHOE CHALOEM PHRA KIAT, CHANGWAT NAKHON RATCHASIMA

Abstract

Thaisin sandpit in Tambon Tha Chang, Amphoe Chaloem Phra Kiat, Changwat Nakhon Ratchasima consists of various sizes of sediments. Aerial photograph interpretation shows that Thaisin sandpit is located in Meander scar. Stratigraphic successions suggested that paleoenvironment of Thaisin sandpit was fluvial deposit with various events. Three units were interpreted. Unit 1 is the upper unit, sedimentary layers are composed of channel sediments with poorly-sorted, medium to very coarse sand and gravel with cross-bedding structure and plant fragments. Unit 2, consists of sediments deposited in flood plain environment with well-sorted, root traces, bioturbation structure and few plant fragments. Unit 3, the lower most part, contains sediments in flood situation with varied size of sediments, cross-bedding and large plant fragment, tight pack dark gray color sediments with peat at the bottom. Seven proboscidean fossils teeth specimens, 2TE1, 3TE1, 3TE2 4TE1, 6TE1, 6TE2 and 9TE1, were found from Thaisin sandpit. They were studied and identified by comparison of their external morphology and measurement methods of teeth. Two genera of proboscidean fossils were classified; Stegodon and Stegolophodon. Statistical analysis was also used for clustering fossils into groups. Maximum width, crown height and enamel thickness of teeth into two groups. The first group is composes of T2TE1, 3TE1, 3TE2 and 9TE1, another group contains 4TE1, 6TE1 and 6TE2. The results of both external morphology and the clustering analysis are similar. Paleoecology was described from the relationship between fossil and its environment. The dietary of proboscidean shows the evolution trend of teeth. Stegodon shows the higher crown, wider tooth and thicker enamel than Stegolophodon. These indicated they were the grasser than browser. The proboscidean might live not far from the forest and river, while the turbulence weather was carried bones and trees along the river then deposited rapidly.