Species selection, covariation of species’ traits with their net diversification rates, is an important component of macroevolution. Most studies have relied on indirect evidence for its operation and have not quantified its strength relative to other macroevolutionary forces. We use an extension of the Price equation to quantify the mechanisms of body size macroevolution in mammals from the latest Palaeocene and earliest Eocene of the Bighorn and Clarks Fork Basins of Wyoming. Dwarfing of mammalian taxa across the Palaeocene/Eocene Thermal Maximum (PETM), an intense, brief warming event that occurred at approximately 56 Ma, has been suggested to reflect anagenetic change and the immigration of small bodied-mammals, but might also be attributable to species selection. Using previously reconstructed ancestor–descendant relationships, we partitioned change in mean mammalian body size into three distinct mechanisms: species selection operating on resident mammals, anagenetic change within resident mammalian lineages and change due to immigrants. The remarkable decrease in mean body size across the warming event occurred through anagenetic change and immigration. Species selection also was strong across the PETM but, intriguingly, favoured larger-bodied species, implying some unknown mechanism(s) by which warming events affect macroevolution.
Electronic supplementary material, Dataset S1
Mean body sizes, approximated from the natural logarithm of the lower first or second molar area, and the proposed evolutionary relationships between mammalian genera from the early and middle Clarkforkian (Cf1 to Cf2) of the Bighorn and Clarks Fork Basins, Wyoming, USA. Notably, each taxon is assigned an index number (i.e., ‘Index’ column). The mean body size of each taxon is provided for each of the time intervals that the taxon occurs (i.e., ‘size_i’ is the mean body size of the taxon in the older time interval and ‘size_j’ is the mean body size of the taxon in the younger time interval; NA indicates that the taxon does not occur in that time interval). Evolutionary relationships are indicated with specific reference to the index number of taxa, with a number in the ‘ancestor’ column indicating that the taxa is a descendant of the referenced index number; zeros in the ‘ancestor’ columns indicates that there is no ancestor for that taxon in the dataset. For instance, Haplomylus_palustris (i.e., Index taxon 1) does not have an ancestor in the dataset and a zero is recorded within the ‘ancestor’ column for this taxon. However, in the same dataset, Haplomylus_simpsoni (i.e., Index taxon 2) does have an ancestor in the dataset; this ancestor is Haplomylus_palustris and a 1 is recorded in ‘ancestor’ column referring to the index number of Haplomylus_palustris.
Electronic suppl. mat., Dataset S1, Cf1 to Cf2.csv
Electronic supplementary material, Dataset S2
Mean body sizes, approximated from the natural logarithm of the lower first or second molar area, and the proposed evolutionary relationships between mammalian genera from the middle and late Clarkforkian (Cf2 to Cf3) of the Bighorn and Clarks Fork Basins, Wyoming, USA. For details of the dataset see caption for electronic supplementary material, dataset S1.
Electronic suppl. mat., Dataset S2, Cf2 to Cf3.csv
Electronic supplementary material, Dataset S3
Mean body sizes, approximated from the natural logarithm of the lower first or second molar area, and the proposed evolutionary relationships between mammalian genera from the late Clarkforkian and earliest Wasatchian (Cf3 to Wa0) of the Bighorn and Clarks Fork Basins, Wyoming, USA. For details of the dataset see caption for electronic supplementary material, dataset S1.
Electronic suppl. mat., Dataset S3, Cf3 to Wa0.csv
Electronic supplementary material, Dataset S4
Mean body sizes, approximated from the natural logarithm of the lower first or second molar area, and the proposed evolutionary relationships between mammalian genera from the earliest to early Wasatchian (Wa0 to Wa1/2) of the Bighorn and Clarks Fork Basins, Wyoming, USA. For details of the dataset see caption for electronic supplementary material, dataset S1.
Electronic suppl. mat., Dataset S4, Wa0 to Wa1_2.csv
