The Evolution of Body Size, Cope's Rule and the Origin of Amniotes

Abstract

The evolution of body size in tetrapods is assessed using a database that includes 107 early stegocephalian species ranging in time from the Frasnian (Upper Devonian) to the Tatarian (Upper Permian). All analyses use methods that incorporate phylogenetic information (topology and branch lengths). In all tests, the impact of alternative topologies and branch lengths are assessed. Previous reports that raised doubts about the accuracy of squared-change parsimony assessment of ancestral character value appear to have used datasets in which there was no phylogenetic signal. Hence, squared-change parsimony may be more reliable than suggested in recent studies, at least when a phylogenetic signal is present in the datasets of interest. Analysis using random taxon reshuffling on three reference phylogenies shows that cranial and presacral length include a strong phylogenetic signal. Character optimization of body size in stegocephalians using squared-change parsimony on a time-calibrated phylogeny incorporating branch length information is used to test a previously published scenario on the origin of amniotes and of the amniotic egg that implies that the ancestors of amniotes were small (no more than 10 cm in snout-vent length), and that their size increased subsequent to the appearance of the amniotic egg. The optimization suggests that first amniotes were somewhat larger than previously hypothesized; the estimated snout-vent length is about 24 cm, and the lower end of the 95% confidence interval of the phylogeny that yields the smallest inferred size suggests that no ancestor of amniotes measured less than 12 cm in snout-vent length. Character optimization, permutational multiple linear regressions, and independent contrast analyses show that Cope's rule of phyletic size increase applies to early reptiliomorphs but that it does not apply to early stegocephalians globally.

Habitat changes and changing predatory habits in North American fossil canids

“…As we are only interested in quantifying the presence of phylogenetic signal, instead of the strength of the phylogenetic signal, we used the permutation approach developed by Laurin 46 , extended for multivariate analysis by Klingenberg and Gidaszewski 47 , and applied to shape data by other authors (for example, refs [48][49][50][51][52][53][54], to simulate the null hypothesis of complete absence of phylogenetic signal in elbow shape. The mean species shapes are randomly distributed as the tips of the phylogeny in 10,000 permutations, and for each permutation, the tree length was computed.…”

Phylogenetic approaches in comparative physiology

“…Extremely high measurement error could have a similar effect, but would also make us seriously doubt that the data were good enough for any sort of analysis. As discussed below, the issues of high trait lability and/or high measurement error can be addressed empirically, and recent studies have found that most traits do indeed exhibit phylogenetic signal, indicating that a star phylogeny does not provide a good fit to the data (Freckleton et al, 2002;Blomberg et al, 2003;Tieleman et al, 2003;Ackerly, 2004;Al-kahtani et al, 2004;Ashton, 2004a,b;Hutcheon and Garland, 2004;Laurin, 2004;Rezende et al, 2004;Rheindt et al, 2004;Ross et al, 2004;Muñoz-Garcia and Williams, in press). Second, it is important to consider what is meant by the 'branch lengths' of a phylogenetic tree that is used for analysis.…”

“…In such cases, it is often prudent to perform computations with more than one set of branches as a sensitivity analysis for the conclusions (e.g. see Ashton, 2004b;Hutcheon and Garland, 2004;Laurin, 2004). Similarly, some studies use multiple phylogenies (topologies) (e.g.…”

Ecomorphological determinations in the absence of living analogues: the predatory behavior of the marsupial lion (Thylacoleo carnifex) as revealed by elbow joint morphology

“…3) with Mesquite (Maddison and Maddison 2011). We then quantified the phylogenetic signal in elbow shape and size using a permutation test developed by Laurin (2004) for univariate traits, and extended for multivariate analyses by Klingenberg and Gidaszewski (2010), to simulate the null hypothesis of complete independence (e.g., Gidaszewski et al 2009;Figueirido et al 2010Figueirido et al , 2013Klingenberg and Marugán-Lobón 2013;Martín-Serra et al 2014a, 2014b using MorphoJ (Klingenberg 2011).…”