Lineage-through-time plots can be used to record the accumulation of species over time in a molecular phylogeny. The shape of the LTT plot can be summarized by the γ-statistic of Pybus and Harvey (2000).
	Incorrect model specification during phylogenetic inference can cause the γ-statistic of the inferred phylogeny to have a negative value even if the true rate of lineage proliferation was constant over time (γ = 0).