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. 2022 Oct 30;12(11):e9432.
doi: 10.1002/ece3.9432. eCollection 2022 Nov.

Tooth marker of ecological abnormality: The interpretation of stress in extinct mega herbivores (proboscideans) of the Siwaliks of Pakistan

Muhammad Ameen  1   2 , Abdul Majid Khan  1 , Rana Manzoor Ahmad  3 , Muhammad Umar Ijaz  4 , Muhammad Imran  1
Affiliations

Tooth marker of ecological abnormality: The interpretation of stress in extinct mega herbivores (proboscideans) of the Siwaliks of Pakistan

Muhammad Ameen et al. Ecol Evol. .

Abstract

Climate affects living ecosystems and defines species physiology. Climate change causes certain stress on animals, recorded as Enamel Hypoplasia (EH). Proboscideans, the mega herbivores, were extensively represented in the Siwaliks of Pakistan between the Middle Miocene to Pleistocene (~15.99-~0.6 Ma). This study was carried out on 15 species from 9 genera and 4 families using 319 teeth from 266 individual quarries. Our results revealed that 20.06% (64/319) of teeth were infected by EH. Family Deinotheriidae faced higher stress during the terminal of the Middle Miocene (EH 25%). Dental characters of deinotheres indicated that this family preferred soft vegetation like C3 plants and failed to survive in grassland ecology at the onset of the Late Miocene (~10-9 Ma). Gomphotheriidae (EH 21.05%) and Stegodontidae (EH 23.40%) survived through warm and dry climatic conditions of the Late Miocene, but could not survive the cool and dry climate of Plio-Pleistocene where grasslands were abundant with less browsing activity. Family Elephantidae (EH 8.47%) was successful in drier conditions and utilized the exclusive C4 diet in open grasslands as efficient grazers, indicated by their tooth morphology. Elephantids were dominant of the proboscideans in open grassland and drier climate during Plio-Pleistocene in the Indian subcontinent. We assume that change in the Siwalik palaeoenvironment was governed by a microclimate.

Keywords: Siwaliks; enamel; hypoplasia; palaeoecology; proboscidea.

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Conflict of interest statement

The authors declare no conflict of interest in this study.

Figures

FIGURE 1
FIGURE 1
Indicating the stratigraphic range of the family Deinotheriidae in the Siwaliks of Pakistan (Khan et al., ; Patnaik, 2013).
FIGURE 2
FIGURE 2
The stratigraphic range of genera of the family Gomphotheriidae in the Siwaliks of Pakistan (Abbas et al., ; Behrensmeyer & Barry, 2005).
FIGURE 3
FIGURE 3
The stratigraphic range of genera of the family Stegodontidae in the Siwaliks of Pakistan (Osborn, ; Saegusa, ; Saegusa et al., ; Tassy, 1983).
FIGURE 4
FIGURE 4
The stratigraphic range of different members of the family Elephantidae in the Siwaliks of Pakistan (Agarwal et al., ; Dennell et al., ; Hussain et al., ; Nanda, 1997).
FIGURE 5
FIGURE 5
Longitudinal cross section of mammalian (proboscidean) tooth for the development of enamel and dentine, a diagrammatical representation of the formation of EH.
FIGURE 6
FIGURE 6
The pictographic representation of selected molars from the Siwalik Proboscidean families showing enamel hypoplasia where the specimen a = Deinotheriidae, b = Gomphotheriidae, c = Elephantidae, and d = Stegodontidae. The marks and measurements of EH are indicated by an arrow in millimeters from the root crown junction. Scale bar of 10 mm is used.
FIGURE 7
FIGURE 7
Comparison of the occurrence of stress as EH in the studied Siwalik mammalian families. Giraffidae and Tragulidae (Ahmad et al., 2018, 2020), Rhinocerotidae (Roohi et al., 2015).
FIGURE 8
FIGURE 8
Genus level comparison of the Siwalik stress events on different proboscideans, each color indicates a different family (green = Deinotheriidae, red = Gomphotheriidae, yellow = Stegodontidae, blue = Elephantidae); length of the color bars indicate the frequency of environmental stress during different time intervals of the Siwaliks palaeoenvironment (Barry et al., ; Barry & Flynn, ; Dennell et al., 2006).
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References

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