Rainfall variations dictated species evolution and mass extinctions
Rains predate life on Earth, says one of the dominant theories about the origin of life. In fact, they have influenced evolution. For instance, the Asian monsoon, which took form around 23 million years ago,and underwent variations in intensity,impacted the evolution of a group of rodents, named Rhizomyinae, in the Shiwalik mountain range of the Himalayas, says a new study. This group of rodents includes the Asian bamboo rats and mole rats.
Terrestrial and freshwater fossils of 38 species, deposited over millions of years in various parts of the mountain range in Pakistan,India,Nepal and Bhutan were analysed in the study published on March 11 in Scientific Reports. The study showed that the periods of the weakening of the monsoon had a huge impact on the evolution of the rodents.
A species’ skull shape, cheek depth and teeth structure indicate the kind of food available and the vegetation, in turn, shows the strength of the monsoon. A weakening of the monsoon about 10 million years ago led to sparser vegetation and more open landscapes, leaving the rodents open to predators,and making food scarce.This led them to seek shelter underground. Subsequently, these rodents evolved to have a skull shape and cheek structure that would enable them to dig with their jaws, rather than their paws, and to feed on underground vegetation that used to be drier and coarser than that which is found above the ground. The species that could not adapt became extinct. There were also several instances of migration of species towards Africa.
The Rhizomyinae clade of rodents