Combining two dockerfiles with different FROM fields, in one

I have two separate application that consist of different dockerfiles.

The one dockerfile starts with FROM ubuntu

while the other one starts with FROM continuumio/miniconda3

Now i want to merge these two applications into one, and this means i have to create one dockerfile with all the necessary packages that my application will utilize.

Given that the two dockerfiles have different FROM fields, how can someone proceed to combine them into one?

Can i use two FROM fields, or do i have to see the packages that one has somehow, if they can be put into another?