I REALLY NEED HELP The oldest bird fossils date back to around 150 million years ago. The number of different bird species in the fossil record remained small for the next 90 million years. Around 65 million years ago, the dinosaurs went extinct. Around 60 million years ago there were thousands of bird species that occupied a variety of habitats.

Which of the following explanations BEST describes the increase in the number of bird species between 65 and 60 million years ago?

A.
It took over 90 million years for enough random mutations to occur in early birds to provide variation needed for speciation.

B.
After the extinction of the dinosaurs, many niches opened up, allowing for widespread speciation of birds.

C.
It took over 90 million years for the early birds to disperse over geographic areas to provide variation needed for speciation.

D.
After the extinction of the dinosaurs, bird population sizes increased, allowing birds to be more easily found in the fossil record.