About 100,000 years ago, megabeasts started disappearing from the face of the planet — the 13-ton elephant ancestor Stegodon, the 600-kg lizard-like Megalania, the 100-kg Giant Beaver. It was a period of significant climate change. It was also when prehistoric humans started expanding their footprint outside Africa. Wherever humans arrived, large animals died out. But not in Africa and south Asia.
It's a pattern that has puzzled palaeontologists for decades. But while Africa has been studied for six decades, India has never been. In a new study, for the first time, researchers from Yale University, the Smithsonian’s National Museum of Natural History, the University of Nebraska and the George Mason University have compiled a database of recent fossils from the Indian subcontinent to fill this gap.
Lead author Dr Advait Jukar said “co-evolution” has been used to explain the survival in Africa. “Co-evolution is this interesting hypothesis developed in the 1960s by American palaeoarchaeologist Paul Martin … He saw we still have a lot of large animals in Africa, but not in the Americas. So, he thought about it and came up with the idea that because humans had evolved in Africa, other large species had evolved along-side them,” Jukar told TOI. “It’s kind of like an evolutionary rat race, where one species has to be better than the other to survive.”
Advait Jukar studying tooth from a Stegodon from India at Natural History Museum, London
So, if humans got better at hunting, animals would get better at escaping. If humans lived in riverine plains, animals would move into the safety of dense forests. “We don’t know what the exact mechanism is. We just know, based on the patterns we see, that this is a likely hypothesis to explain the survival and extinction pattern,” Jukar said. This worked for Africa. But India remained a mystery.
Indian megafauna samples that were studied
Jukar’s study documents the extinction of five large mammals — two massive elephant relatives (Palaeoloxodon namadicus and Stegodon namadicus), a prehistoric hippo (Hexaprotodon), a wild zebra-like horse (Equus namadicus), and the wild ancestor of the modern domestic Zebu cattle (Bos namadicus) — on the Indian subcontinent. Along with these five species, they also document the local extinction of ostriches, which are only found in Africa today.
With fossil records from 25 sites in India and statistical analysis, they put together data on when these animals went extinct, if they were larger than survivors, the extinction rate here and how that compared to those in other parts of the world. Then, they compared it with historical climate data and records of the emergence of humans to see if causal patterns emerged.
Indian megafauna chronology
What they found was that these five species represent only ~4% of India’s land mammals, a very small number compared to the rest of the world, but very similar to what has been known from Africa.
The disappearance of large animals appears to have begun some 30,000 years ago and continued up to 8,000 years ago. This is around the time that there was a drop in the Indian Monsoon (there were three prominent cold and dry periods, when low monsoon intensity led to droughts), the paper said. Rain-fed rivers like Son and Belan show signs of sedimentation between 40,000 and 16,000 years ago. The Ganga river valley also showed reduced activity between 28,000 and 15,000 years ago. Yet, they noted, “all of the species we document going extinct survive several intervals of prolonged drought during the late Pleistocene (126,000 to 12,000 years ago).” Even the arrival of Homo sapiens from Africa 60,000 years ago, clearly, does not coincide with the extinctions. In fact, on the Indian subcontinent, there is a 30,000-year gap between the appearance of humans and disappearance of megafauna, like the Stegodon.
The only clear link, it turns out, is with the time that humans start using projectile tools. The study said, “The timing of the extinctions does correlate with a shift in tool technologies and an increase in human population density. A shift to microliths (sharp flint-like small tools of stone, used as spearheads) during the Middle Palaeolithic-Late Palaeolithic transition (45,000–35,000 years ago) indicates the use of composite tools, such as projectiles and bows and arrows, thus making hunting more efficient.”
Because the extinctions were limited to large species, Jukar argues for a strong human role as a primary cause. However, we still have elephants, tigers, and rhinos in India.
Four factors may have helped large animals survive in the Indian subcontinent. India has been home to different species of humans in the past, just like Africa, with a record going back almost 2 million years. Jukar said this would have led to co-evolution, just like it’s been hypothesized in Africa. Additionally, prehistoric humans here hunted smaller prey like monkeys or more abundant game like deer, evidence of which has been found in Sri Lanka, and butchery sites in India. Then, there is the beginning of cattle domestication some 9,000 years ago, as evidence from Mehrgarh in Baluchistan suggests, which means people started settling down. Finally, the large geographic area over which animals were distributed — many found in India ranged all the way from Turkey to southeast Asia until very recently – may have helped them survive. “The species that go extinct were all endemic [found nowhere else] to the Indian subcontinent … with no source population outside to ‘rescue’ collapsing populations.”
“Up until our study, no one had synthesised any of these records to try and figure out what was going on in India … I can count the number of vertebrate palaeontologists in India on both hands and I am one of them,” Jukar said. “India has one of the longest records of fossil mammals anywhere on the planet. We have a record in the Siwalik, which goes back about 24 million years. The only other places where we get comparable records are North America and parts of China. In India, research has been held back because of a lack of resources.”