Were late Gomphotheres (Plio-Pleistocene) of the Siwaliks at more Stress as Compared to early Gomphotheres (middle to late Miocene)?

Muhammad Ameen,Amtur Rafeh,Ayesha Iqbal,Muhammad Tahir Waseem,Abdul Majid Khan,Muhammad Imran,Rana Manzoor Ahmad

doi:10.35691/jbm.0202.0158

Muhammad Ameen, Amtur Rafeh + Show 5 more

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https://doi.org/10.35691/jbm.0202.0158

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Abstract

Gomphotheres existed in the Siwaliks from the middle Miocene (14.2Ma) to the middle Pleistocene (0.8Ma) and became extinct later on. In this paper, we tried to discuss the reasons of such extinction of gomphotheres in the lower Pleistocene time span by considering Linear Enamel Hypoplasia (LEH) among 114 isolated tooth samples to assess whether ecological changes correlate with the stress factor in gomphotheres. For this purpose, the Siwalik gomphotheres were divided into two Groups viz. early gomphotheres (middle Miocene to late Miocene) and late gomphotheres (Pliocene to middle Pleistocene). We presented the hypothesis, that as the gomphotheres are characterized by the brachydonty and relied on browsing for their feeding while inhabiting the semi forest land setting thus, expected to have higher stress in Plio-Pleistocene time span as vegetational change around ~6 Ma may have exerted stress on late gomphotheres. The results for the occurrence of frequency of LEH indicated severe ecological stress in late gomphotheres (33%). The significant differences were found (P < 0.05) among the early gomphotheres and late gomphotheres which can be correlated to the vegetational change from C3 to C4, higher aridity indices and intensified seasonality after the late Miocene vegetational shift which may have resulted in substantial faunal turnover, extinction and speciation. We assume that such palaeoecological changes forced a competition with more pronounced grazers like of family Elephantidae and Bovidae resulting in extinction of gomphotheres during the late Pleistocene in the Siwaliks of Pakistan.

Highlights

The Siwaliks of Pakistan ranges from the middle Miocene to the latePleistocene time span and exhibit a rich vertebrate diversity including perissodactyls, artiodactyls, rodents, proboscideans, carnivores and hominids (Dennell et al, 2006; Badgley et al, 2008; Flynn et al, 2016)
The Siwalik genus, Anancus represented by two species, A. sivalensis and A. osborni which showed 33.33% occurrences of Linear Enamel Hypoplasia (LEH)
The findings showed that the lowest number of teeth defected with LEH were found 15.79% in P. chinjiensis and 16.36% in C. corrugatus whereas, the species A. sivalensis having 37.50% of LEH was found to have the highest number of defected teeth

Summary

Introduction

The Siwaliks of Pakistan ranges from the middle Miocene to the latePleistocene time span and exhibit a rich vertebrate diversity including perissodactyls, artiodactyls, rodents, proboscideans, carnivores and hominids (Dennell et al, 2006; Badgley et al, 2008; Flynn et al, 2016). The Siwaliks of Pakistan ranges from the middle Miocene to the late. The Potwar Plateau (Figure 1) has yielded a rich fossil record and has been a center of focus for palaeontologists from all over the globe from a century (Falconer and Cautley, 1868; Pilgrim, 1910, 1913, Sarwar, 1977; Barry et al, 1982, 2002, 2013 etc.). The samples have been taken throughout the Siwalik series to assess that how palaeoecological changes forged the phylogeny of gomphotheres. This study deals with the hypothesis that, how ecological changes shape up the phylogeny of the Siwalik gomphotheres after the late Miocene transition (Cerling et al, 1993; Barry et al, 2002, 2013). The present work is the estimation of palaeoenvironmental stress among Gomphotheres before and after the transition

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