Provincialization of terrestrial faunas following the end-Permian mass extinction

Abstract

In addition to their devastating effects on global biodiversity, mass extinctions have had a long-term influence on the history of life by eliminating dominant lineages that suppressed ecological change. Here, we test whether the end-Permian mass extinction (252.3 Ma) affected the distribution of tetrapod faunas within the southern hemisphere and apply quantitative methods to analyze four components of biogeographic structure: connectedness, clustering, range size, and endemism. For all four components, we detected increased provincialism between our Permian and Triassic datasets. In southern Pangea, a more homogeneous and broadly distributed fauna in the Late Permian (Wuchiapingian, ∼257 Ma) was replaced by a provincial and biogeographically fragmented fauna by Middle Triassic times (Anisian, ∼242 Ma). Importantly in the Triassic, lower latitude basins in Tanzania and Zambia included dinosaur predecessors and other archosaurs unknown elsewhere. The recognition of heterogeneous tetrapod communities in the Triassic implies that the end-Permian mass extinction afforded ecologically marginalized lineages the ecospace to diversify, and that biotic controls (i.e., evolutionary incumbency) were fundamentally reset. Archosaurs, which began diversifying in the Early Triassic, were likely beneficiaries of this ecological release and remained dominant for much of the later Mesozoic.

Keywords: biogeography; biotic recovery; complex networks; macroevolution; paleoecology.

Fig. 1.

Paleogeographic map of southern Pangea with stars indicating the positions of the five Permian and Triassic fossiliferous areas analyzed (from left to right: Karoo Basin of South Africa; Luangwa Basin of Zambia; Chiweta beds of Malawi; Ruhuhu Basin of Tanzania; Beacon Basin of Antarctica). Corresponding faunal data from India and Namibia are discussed in the SI Text. Modern outlines of Africa (excluding Madagascar) and Antarctica (excluding East Antarctica) are highlighted. Early Triassic paleogeography (∼250 Ma) is based on data originally published by Lawver et al. (40).

Fig. 2.

Bipartite networks exemplifying minimum to maximum scores of BC. Brown circles denote localities (geographic areas), tan circles denote taxa that occur at a single locality, and yellow circles denote taxa present at two or more localities. A taxon is connected to a locality if it occurs there.

Fig. 3.

Biogeographic structure of southern Pangean tetrapod assemblages before and after the Permian-Triassic mass extinction. (A) Late Permian terrestrial vertebrate assemblages show high connectedness and are similar across regions. Early Middle Triassic faunas show increased biogeographic separation that corresponds to faunal differentiation among fossiliferous basins. Asterisks denote approximate faunal horizon on the geological timescale (geochronology from ref. 41). Color codes correspond to those in Fig. 2. E, Early; L, Late; M, Middle. (B–E) Histograms depicting the distribution of bootstrap analyses of four measures of biogeographic structure. Values for network clustering are given in bits (22), with higher values indicating less distinct subunits in the bipartite network. Recovery from the end-Permian crisis resulted in significant differences in biogeographic connectedness, network clustering, range size, and proportion of endemics (Welch two sample t test, P << 0.01 for each; bootstrap data were normally distributed), indicating increased provincialism in the Triassic.