Figure S4 from Probabilistic divergence time estimation without branch lengths: dating the origins of dinosaurs, avian flight and crown birds
2016-11-01T11:00:23Z (GMT) by
Figure to demonstrate that the node-dating algorithm of Hedman is not generalisable to a tree-dating algorithm. Outgroup sequences for three nodes (X-Z) on a hypothetical phylogenetic tree of six fossil taxa (A-F) with sampled ages (T1-T6). Note that for the standard (non-conservative) Hedman approach taxon C is re-dated as T5, the same age as the oldest member (B) of its sister clade (AB), biasing the date of node Y towards a minimum possible age (invalidating the standard approach). Whereas under the conservative Hedman approach taxon C is ignored, as it is younger (T6) than the lower bound for Y set by node AB (T5). Under the conservative scenario the sequence of outgroup taxa for nodes X and Y are identical, meaning branch XY would have zero-length (invalidating the conservative approach). Due to these problems in the present paper only nodes X and Z are considered dateable using the Hedman algorithm (conservative approach), whereas node Y would be dated by making random draws from a uniform distribution bounded by separate random draws from the posterior distributions of nodes X and Z.