Fig. 2

An updated timeline of lentivirus evolution. A time-calibrated phylogeny of mammalian species showing the known extent of association between lentiviruses and mammals, based on data obtained from TimeTree [44]. The scale bar shows time in millions of years before present. Brackets and bars to the right of taxa labels indicate host taxonomic groups. Yellow shapes on terminal nodes indicate that host species have known associations with endogenous lentiviruses (squares) or exogenous lentiviruses (circles). The timeframe of endogenous lentivirus presence in each mammalian lineage is indicated by shaded boxes behind clades, with colours indicating biogeographic associations of hosts within each clade following the key. White triangles at tree tips indicate host species or groups that have not yet been associated with any lentiviruses (endogenous or exogenous). Shapes on branches and internal nodes represent age calibrations for lentiviruses. Two-letter codes adjacent internal markers indicate the type of calibration being shown, as follows: AO = identification of an ancient ortholog; MC = application of a molecular clock to neutrally diverging sequences; CD = assumption of codivergence with hosts; BG = assumption of presence in biogeographic area inhabited by ancestor of species groups that are now biogeographically separated – note that this assumes no transfer between the respective regions identified by derived host species. Colours on diamond-shaped node markers indicate the known biogeographic range of ancestral hosts, following the key. The colonisation of Madagascar by lemurs (BG2) is thought to have occurred ~ 60 million years ago (Mya) [40, 41]