Before we take a look at the early Oligocene I want to show you here a hypothetical encounter of a Plalophoraptor populator and two Thylacosmilus.
Palalophoraptor was maybe the first really big member of the Monopterna, large specimens reach perhaps 5 m in length. The few bones which were collected suggest that the animal wasn't the best flyer but more are like secretary birds.
After the arrival of the Aquilapoda from North america these giant Lophoraptorids extinct (Together with Thalacosmilus) and only a few smaller species remain.
The first drawing I made of the animal: [link]