Some studies about Earth's fosilized plants/animals mention a "Oligo-Miocene radiation".
Our study therefore strengthens previous suggestions that the absence of very large penguins today is likely due to the Oligo-Miocene radiation of marine mammals.
from Mayr et al (2017), doi: 10.1038/s41467-017-01959-6
Molecular phylogeny and dating reveals an Oligo-Miocene radiation of dry-adapted shrubs (former Tremandraceae) from rainforest tree progenitors (Elaeocarpaceae) in Australia
from Crayn et al. (2006), doi: 10.3732/ajb.93.9.1328, see also www.ncbi.nlm.nih.gov/pubmed/21642198
So, what is this "Oligo-Miocene radiation" ?