April 10, 2014

Ancient Indian mammals’ remarkable story of survival

Mammalian extinctions during the past several hundred thousand years have been a major focus for evolutionary biologists, geologists, and archaeologists, often being linked to climate change and human hunting.

Now an international research team, including Distinguished Professor Richard (Bert) Roberts and Dr Zenobia Jacobs from the University of Wollongong’s Centre for Archaeological Science, has revealed how mammals on the Indian subcontinent have shown great tolerance to survive large-scale climatic, volcanic and human impacts.

Their report was published in this week’s Proceedings of the National Academy of Sciencesof the USA (PNAS), which is one of the world’s leading multidisciplinary scientific journals.

The new research shows that 20 of 21 mammal groups (taxa) present on the Indian subcontinent up to 200,000 years ago are still present today, in contrast to the mass extinction of many other taxa (particularly large animals, known as megafauna) in other regions of the globe.

The team’s results for India are similar to fossil record trends elsewhere in southern Asia, but contrast with much higher levels of faunal extinctions in the Americas, Eurasia and Australia.

The new findings highlight the importance of refugia (areas that have escaped ecological changes occurring elsewhere) for animal conservation, say the authors.

Their work also argues for a more "nuanced ecological understanding" in debates over the fate of Australia's giant marsupials, birds and reptiles, rather than the entrenched support for either climate- or human-induced extinction of our megafauna.

The new findings are based on fossil finds in two caves in the Billasurgam cave complex in Andhra Pradesh state in southern India.

The fossils found in the two caves constitute the oldest, well-dated faunal succession for the Indian subcontinent, stretching from 240,000 years ago to the last 10,000 years.

Professor Roberts and Dr Jacobs provided a timeline for the fossils, using single-grain optically stimulated luminescence (OSL) methods to date the cave deposits.

The authors tracked species diversity through several major natural events, including two glacial–interglacial cycles and a volcanic super-eruption 74,000 years ago, as well as the arrival of modern humans in India within the last 100,000 years.

Examination of the fossils shows a diverse range of ancient mammals, including small to large carnivores, primates, small to large bovids (cloven-hoofed mammals) and cervids (deer family), rhinoceros and wild Equus (such as horses, donkeys and zebras).

One of the primates, a type of baboon that is today restricted to the highlands of Ethiopia, lived in southern India until 100,000 years ago and may have survived until more recently.

The fossil record also shows that mammals now found in other regions of India were once present at Billasurgam.

Shifts in the geographic range of extant species suggest they may have survived by retreating to "mixed, interconnected habitats", the authors say.

In an interview with ABC Science, senior author of the report, archaeologist Professor Michael Petraglia, from the University of Oxford, says that climate change and population growth in India in the past 10,000 years are leading to the further restriction of mammals such as the rhino and wild ass.

"As the inter-connection between mosaic habitat declines, animals are finding themselves increasingly isolated and geographically circumscribed," he says.

"Conservation efforts need to be placed on preserving these habitats and their inter-connection, or else we can expect a significant reduction in the genetic diversity of mammal populations, and even their extinction."

Professor Roberts, who has worked previously on the extinction of the Australian megafauna, notes that the results from India mirror recent findings from Australia that show the combined effects of climate change and human disturbance.

“The Billasurgam fossil record shows that the impact of human arrival, climate change and other natural events such as volcanic eruptions will vary from region to region, so untangling these different influences is the next great challenge”, he told ABC Science.