Parsimony‐based test for identifying changes in evolutionary trends for quantitative characters: implications for the origin of the amniotic egg

Abstract

The origin of the amniotic egg was a major event in vertebrate evolution and is thought to have contributed to the spectacular evolutionary radiation of amniotes. We test one of the most popular scenarios proposed by Carroll in 1970 to explain the origin of the amniotic egg using a novel method based on an asymmetric version of linear parsimony (aka Wagner parsimony) for identifying the most parsimonious split of a tree into two parts between which the evolution of the character is allowed to differ. The new method evaluates the cost of splitting a phylogenetic tree at a given node as the integral, over all pairs of asymmetry parameters, of the most parsimonious costs that can be achieved by using the first parameter on the subtree pending from this node and the second parameter elsewhere. By testing all the nodes, we then obtain the most parsimonious split of a tree with regard to the character values at its tips. Among the nine trees and two characters tested, our method yields a total of 517 parsimonious trend changes in Permo-Carboniferous stegocephalians, a single one of which occurs in a part of the tree (among stemamniotes) where Carroll's scenario predicts that there should have been distinct changes in body size evolutionary trends. This refutes the scenario because the amniote stem does not appear to have elevated rates of evolutionary trend shifts. Our nodal body size estimates offer less discriminating power, but they likewise fail to find strong support for Carroll's scenario.

Crocodylomorph cranial shape evolution and its relationship with body size and ecology

“…Adams & Collyer, ; Bastide, Ané, Robin, & Mariadassou, ), many of which assume evolution under a nonuniform Ornstein–Uhlenbeck [OU] process (although methods that assume other models/processes are also available; e.g. Rabosky, ; Castiglione et al., , ; Didier, Chabrol, & Laurin, ). In particular, the combination of using multivariate data (such as shape data derived from geometric morphometric methods) and fossils as tips in a time‐scaled tree (i.e.…”

Can We Reliably Calibrate Deep Nodes in the Tetrapod Tree? Case Studies in Deep Tetrapod Divergences

“…The assembly of both the amphibian crown group and the amniote crown group are thought to have largely occurred at small body sizes (Carroll, 1982;Laurin, 2004;Kemp, 2007;Pérez-Ben et al, 2018), although the overall pattern of body size evolution in these clades is under some debate (Didier et al, 2019). Skeletal material from small vertebrates degrades more quickly than bones of larger vertebrates and is preferentially lost from the record (Behrensmeyer et al, 1979).…”

Evolutionary Change in Locomotion Close to the Origin of Amniotes Inferred From Trackway Data in an Ancestral State Reconstruction Approach

“…6. Use of alternative methods for the reconstruction of ancestral states and character evolution: A parsimonybased testing method introduced by Didier et al (2019) for quantitative characters takes branch length into account and aims at the localization of trend changes on a phylogenetic tree. Whether such an approach can detect changes on the lineage connecting last common ancestor of tetrapods and the last common ancestor of amniotesdespite the comparatively low resolution of the trackmaker trees, high age differences between the supposed timing of divergence from the amniote stem lineage and the first occurrence of a trackmaker and poor sampling density for the Mississippian and early Pennsylvanian -remains to be tested.…”

“…Whether the discussed signal reflects an actual pattern could be counter-checked based on measurement data of trackmaker skeletons (e.g., skull length, long bone length, and total limb length). Accordingly, ancestral states could be reconstructed for a skeleton-based body size proxy -which would also have the advantage that it includes a more detailed phylogenetic tree that reflects body size changes more realistically (see Laurin, 2004;Didier et al, 2019 on skull length in amniotes and their relatives; Brocklehurst and Brink, 2017 on synapsid body size). Another idea to cover trackmaker body size with more detailedness would be the inclusion of the somewhat larger record of isolated tracks and couples (instead of only trackways), provided their preservation is good enough for trackmaker assignment.…”

“…Apart from the effects of variability within trackmaker groups and the general uncertainty of nodal reconstructions (see also Laurin, 2004;Didier et al, 2019), ambiguous track-trackmaker correlations and the controversial phylogenetic relationships of the skeletal-morphology-based orthotaxa also contribute to the vagueness. We have compared results for two alternative trees, alternating the position of varanopids as supposed trackmakers of Tambachichnium -with only minor effects regarding the lineage of amniote ancestors.…”