POPULATION ANALYSIS OF THE SILURIAN BRACHIOPOD ATRYPOIDEA FOXI JONES FROM QUJING,YUNNAN PROVINCE
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Abstract:
Since fossil population contains rich ecological information, related studies are important in palaeontology. By researches on population of Atrypoidea foxi Jones,the structure and ecological environment of population can be evaluated.Brachiopods collected from the lower Kuanti Formation exposed at a stone quarry at Longwangmiao Village in Qujing,Yunnan are dominated by Atrypoidea foxi Jones(Brachiopods),with 381 conjoined valves of the species.A good state of preservation suggests the original condition of the population may be revealed.The population structure was analyzed.The sizefrequency curve fitting normal distribution and slightly negatively skewed,suggests the adult individuals are predominant in this population.Survivorship curve is convex from small to adult individuals and concave from adult to old stage,reveal that most individuals can develop to adult even older individuals,which suggests a suitable living environment.Regression analysis shows that some larger individuals tend to be wider;meanwhile,the shell’s thickness is not stable for large individuals.Furthermore,as an individual becomes more convex rather than longer and wider,the depth of its sulcus is increased.Considering the size of brachiopods affected by length,width and thickness,body volume should be adopted as an index to represent body size.Based on a published study and"density method",a new empirical formula is given to calculate body volume of atrypides.
