Figure 1.
Karoo time series and age rank results for observed geologic distributions of maximum basal skull length (lnBSL). A
, Regional patterns of trait evolution in Karoo eutheriodonts (black) (therocephalian subclade = blue; cynodont subclade = gold) fit a non-directional model throughout the Karoo succession (see Table 1). Squares represent clade averages (with 95% confidence intervals), gray circles represent maximum known sizes for each species recorded in a given stratigraphic interval (Ma, millions of years ago). B, Spearman's rank correlation tests on global age rank data (used for the phylogenetic sampling) reveal a weak negative trend in species maximum sizes (ρ = −0.261; p = 0.025) with a short-term bottleneck in size maxima in the Early Triassic Lystrosaurus AZ (arrow). Permian-Triassic boundary (PTB) represented by dashed line.
Table 1.
Time series model fitting of body size evolution in Karoo therocephalians and cynodonts.
Table 2.
Results of rank correlations, Spearman's rho (ρ) and Kendall's tau (τ), for global age ranks.
Figure 2.
Complete reference cladogram with nodes numbered for estimation of patristic distances.
Sources include: therocephalians, Huttenlocker [54], Huttenlocker et al. [33], Sigurdsen et al. [55]; cynodonts, Hopson & Kitching [56], Abdala et al. [45], Sidor & Hancox [57], Ranivoharimanana et al. [60], Oliveira et al. [58], Liu & Olsen [59].
Figure 3.
Ranking of side-branches within the two major subgroups: Therocephalia (A) and Cynodontia (B) (simplified from reference cladogram in Fig. 2).
Table 3.
Results of rank correlations, Spearman's rho (ρ) and Kendall's tau (τ), for clade ranks and patristic distances.
Table 4.
Summary of ancestor-descendant step changes in the therocephalian and cynodont trees (ancestral states reconstructed using squared-change parsimony).
Figure 4.
Spearman's rank correlation tests on clade rank (A, B) and patristic distance (C) versus maximum basal skull length for the global dataset of Middle Permian through Late Triassic eutheriodonts.
Solid circles represent Permian taxa (therocephalian subclade = blue; cynodont subclade = gold), open diamonds represent Early Triassic Lystrosaurus Assemblage Zone (LAZ) taxa, and open circles represent Triassic post-LAZ taxa.
Figure 5.
Cladograms subsampled from five stratigraphic bins for analysis of diversification rate shifts. A
, Tropidostoma Assemblage Zone. B, Cistecephalus Assemblage Zone. C, Dicynodon Assemblage Zone. D, Lystrosaurus Assemblage Zone. E, Cynognathus Assemblage Zone. Gray branches represent ghost lineages for terminal taxa or clades that appear in a succeeding stratigraphic interval. Numbers at nodes represent p-values near or below 0.05 for the Δ1 (top) and Δ2 (bottom) statistics. Significant shifts are observed along the branch between the node of Eutherocephalia and non-Scylacosuchus eutherocephalians for the Tropidostoma AZ subsample (A), and a marginally significant shift is observed along the branch between Eutheriodontia and Eutherocephalia for the Cistecephalus AZ (B).
Figure 6.
Traitgram of body size evolution in a global sample of Permian through Triassic eutheriodonts, approximating an ‘early burst’ Brownian process (EB) of trait evolution.
Arrow denotes location of Lystrosaurus Assemblage Zone taxa along the time-axis. Graphic created using the traitgram() function in ‘picante.’
Table 5.
Phylogenetic model fitting results.
Figure 7.
Ancestral state reconstructions for basal skull length in Permian and Triassic therocephalians.
Colored horizontal bars indicate ranges of tip taxa spanning more than one stratigraphic bin. Note that significant decreases in mean sizes of major subgroups across the Permian-Triassic boundary (dashed line) were associated with the loss of large-bodied taxa and the survival of pre-existing small-bodied taxa or clades. Abbreviations: CiAZ, Cistecephalus Assemblage Zone; CynAZ, Cynognathus Assemblage Zone; DAZ, Dicynodon Assemblage Zone; LAZ, Lystrosaurus Assemblage Zone.
Figure 8.
Ancestral state reconstructions for basal skull length in Permian and Triassic cynodonts.
Colored horizontal bars indicate ranges of tip taxa spanning more than one stratigraphic bin (e.g., Procynosuchus, Cynosaurus). Permian-Triassic boundary indicated by dashed line. Abbreviations: CiAZ, Cistecephalus Assemblage Zone; CynAZ, Cynognathus Assemblage Zone; DAZ, Dicynodon Assemblage Zone; LAZ, Lystrosaurus Assemblage Zone.