Extinction of Siwalik fossil apes: a review based on a new fossil tooth and on palaeoecological and palaeoclimatological evidence

Abstract

We report here a new fossil hominoid tooth from the Late Miocene (~7.8 Ma) of the Hari-Talyangar region, India. The large-sized hominoid M2 is rather bunodont and its occlusal morphology and size are fairly distinctive from both the Sivapithecus sivalensis and Sivapithecus indicus conditions. Correlation between upper and lower molar breadth in extant hominoids and Sivapithecus species suggests that this upper molar fits within an estimated range of Indopithecus (= ‘Gigantopithecus’) M2 variation; a lower M2 of the same taxon is known from the same region. However, molar size and morphology are also consistent with a S. parvada attribution. Therefore its formal taxonomic allocation remains problematic. Sivapithecus was primarily a fruit eater and its teeth do not generally show caries, but the present molar exhibits a large caries, indicating a probable diet of grasses and fruits. The supposed diet of the new fossil tooth suggests that these Late Miocene apes of the Hari-Talyangar region lived in a habitat drier than that of Sivapithecus. A review based on the present fossil and palaeoecological and palaeoclimatological evidence supports a hypothesis that the Siwalik fossil apes disappeared by the Late Miocene because of a decrease in humidity and an increase in seasonality, aridity, and unpredictable climatic conditions brought about by the intensification of the monsoon system, eventually leading to expansion of grasslands at the expense of rainforests.