A new study, cited below, out of China provides insights into why "higher primates" survived and evolved into various clades including humans in Africa, while they went extinct leaving only "lower primates" in Asia.
The key event took place 34 million years ago when the collision of the continental plate that is now the Indian subcontinent hit the rest of Asia resulting in climate changes that destroyed jungles that had been home to primates until then. "Lower primates" managed to survive in the less lush forests that remained, while "higher primates" could not survive without a thriving tropical jungle.
A sharply cooler and drier climate at that time, combined with upheavals of landmasses that forged the Himalayas and the Tibetan Plateau, destroyed many tropical forests in Asia. That sent surviving primates scurrying south, say paleontologist Xijun Ni of the Chinese Academy of Sciences in Beijing and his colleagues. New Chinese finds provide the first fossil evidence that the forerunners of monkeys, apes and humans, also known as anthropoids, were then largely replaced in Asia by creatures related to modern lemurs, lorises and tarsiers. . . .
“The focal point of anthropoid evolution shifted at some point from Asia to Africa, but we didn’t understand when and why the shift occurred until now,” says paleontologist and study coauthor K. Christopher Beard of the University of Kansas in Lawrence.
But the scarcity of Asian primate fossils from that time relative to those from Africa leaves the matter unsettled. Egyptian sites in particular have yielded numerous primate fossils dating from around 37 million to 30 million years ago.
Excavations from 2008 to 2014 in southern China produced 48 teeth, some still held in jaw fragments, from six new fossil primate species, Beard says. These primates were tree dwellers and had assembled in a region located far enough south to retain forested areas. The new finds provide a rare glimpse of Asian primates that managed to weather the climate shift. Fossil teeth of one ancient species look much like those of modern tarsiers. These tiny, bug-eyed primates now live on Southeast Asian islands. “Tarsiers are ‘living fossils’ that can trace their evolutionary history back tens of millions of years in Asia,” Beard says.
Only one Chinese fossil primate comes from an anthropoid, Ni’s group concludes. The researchers classify that animal as part of a line of Asian anthropoids previously identified from roughly 40-million-year-old tooth and jaw fragments found in Myanmar, just across China’s southwestern border (SN: 10/16/99, p. 244).
Only one other Asian site, in Pakistan, has yielded anthropoid fossils of comparable age to the Chinese finds. The Pakistan fossils consist solely of teeth. Asian anthropoids died out a few million years after the continent’s tropical forests began to shrink, Beard suspects.
Investigators already knew that primates’ forest homes in Africa survived the ancient cool down better than those in Asia.The Chinese team also argues, with less definitive support, for an asian origin of higher primates around 55 million years ago. But, "Lemur and loris ancestors must have lived in equatorial Africa and Madagascar by 34 million years ago, as lemurs and loris relatives do today. . . . The oldest known primate fossils, from 56 million to 55 million years ago, come from Asia, Europe, Morocco and North America." So, it is much harder to determine where primates, in general, first evolved.
The new paper is:
X. Ni et al. "Oligocene primates from China reveal divergence between African and Asian primate evolution." 352 Science 673 (May 6, 2016).