Fossil evidence from before 2005 suggested that grasses evolved around 55 million years ago. This date has been pushed back to 66 million years due to the discovery of grass-like phytoliths in dinosaur coprolites from the latest Cretaceous (Maastrichtian) Lameta Formation of India. It was discovered in 2011 that fossils from the same deposit belonged to the modern rice tribe Oryzeae, indicating that major lineages had already undergone significant diversification by this time.
According to Wu, You, and Li (2018), grass microfossils that were taken from the teeth of the hadrosauroid dinosaur Equijubus normani, which were found in northern China and date to the Albian stage of the Early Cretaceous approximately 113–100 million years ago, belonged to primitive lineages within the Poaceae that were in a position that was similar to that of the Anomochlooideae. Currently, these are the earliest known grass fossils.
In the BOP clade, the relationships between the three subfamilies Bambusoideae, Oryzoideae, and Pooideae have been established: Compared to Oryzoideae, Bambusoideae and Pooideae are more closely related to one another. Within the relatively brief space of about 4 million years, this separation took place.
Lester Charles King claims that the spread of grasses in the Late Cenozoic would have altered the patterns of hillslope evolution, favoring convex upslope and concave downslope slopes with no free face. King argued that this was brought on by grass carpets’ slower-acting surface wash, which would have led to a little bit more soil creep.