If we see them and their connection, and the close relatives only see that they have very large winged petioles, that would be the common characteristic between them. They also have anticyaninous (red) growths and young C. maxima, or some adults, have a kaffir lime odor. so the trifoliate is derived characteristics only present in Poncirus and not an ancient characteristic. Also Severina buxifolia, which is a sister branch of citrus, does not have trifoliate leaves, nor do its relatives. so no, it does not seem that the ancestor is a trifoliate plant. Then I upload the photogenic tree that I put together with "all the citrus fruits" discovered to date and on the same scale. 💪