Enamel Hypoplasia Analysis in Giraffids to Compare Stress Episodes in Geological History of the Siwaliks of Pakistan
Enamel Hypoplasia Analysis in Giraffids to Compare Stress Episodes in Geological History of the Siwaliks of Pakistan
Rana Manzoor Ahmad1,2, Abdul Majid Khan1,*, Ghazala Roohi3 and Muhammad Akhtar1
ABSTRACT
Studies on dental enamel hypoplasia have been used by different paleontologists as stress indicator in evaluation of palaeo-environments. The present study involves the analysis of enamel hypoplasia in seven extinct giraffid species to determine and compare stress periods during the early Miocene to Pleistocene ages of the Siwaliks of Pakistan. Enamel hypoplasia is a tooth malady which is caused by the deficiency of food/nutrients. The feeding deficiency is directly linked to the physiological or environmental stress. In this study occurrence of enamel hypoplasia in giraffids has been observed in species of all time intervals between 18.3-0.6 Ma except the time 11.2-9.0 (late Miocene) that has no giraffids with this dental defect. The comparative percentage for occurrence of enamel hypoplasia in giraffids of these Siwalik deposits is early Miocene-early middle Miocene (29%), middle Miocene (20%), late Miocene-early Pliocene (15%), early Pliocene-late Pliocene (26%) and late Pliocene-early Pleistocene (10%). Prevalence of enamel hypoplasia indicates the existence of stress episodes and percentage displays the comparative intensity of these stresses in the Neogene and Quaternary period of the Siwalik region. These stress episodes are due to the climatic, vegetational, ecological and faunal changes during these time spans. These early Miocene to Pleistocene stress events may have played a key role in evolution and speciation of the Siwalik fauna especially the mammals.
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