SAtree.from.fossils: Transforms a tree and fossils dataframe to a combined SA tree.
Description
Sampled ancestors are represented as tips on zero-length edges to maintain compatibility with the ape format.
Tip labels are set to "species id"_"index". The order of the indexes is given by `tip_order`: either the oldest tip of a given species
receives index 1 and indexes increase towards the present (default) or the reverse.
A list of `tree`, the SA tree integrating the fossils, and `fossils`, the fossils object updated with the tip label of each sample.
Arguments
tree
Phylo object.
fossils
Fossils object.
tip_order
Order of indexes to assign to the tips, either `oldest_first` (by default, indexes increase towards the present) or `youngest_first`
(indexes increase towards the past).