Topic
Synapsid
About: Synapsid is a research topic. Over the lifetime, 138 publications have been published within this topic receiving 5152 citations. The topic is also known as: Synapsida.
Papers published on a yearly basis
Papers
TL;DR: The importance of the critical fossils seems to reside in their relative primitive‐ness, and the simplest explanation for their more conservative nature is that they have had less time to evolve.
1,046 citations
TL;DR: It is shown that the mammalian (synapsid) and reptilian lineages show early in their evolutionary histories clear divergences in axial developmental plasticity, in terms of both regionalization and meristic change, with basal synapsids sharing the conserved axial configuration of crown mammals, and basal reptiles demonstrating the plasticity of extant taxa.
Abstract: The development of distinct regions in the amniote vertebral column results from somite formation and Hox gene expression, with the adult morphology displaying remarkable variation among lineages. Mammalian regionalization is reportedly very conservative or even constrained, but there has been no study investigating vertebral count variation across Amniota as a whole, undermining attempts to understand the phylogenetic, ecological, and developmental factors affecting vertebral column variation. Here, we show that the mammalian (synapsid) and reptilian lineages show early in their evolutionary histories clear divergences in axial developmental plasticity, in terms of both regionalization and meristic change, with basal synapsids sharing the conserved axial configuration of crown mammals, and basal reptiles demonstrating the plasticity of extant taxa. We conducted a comprehensive survey of presacral vertebral counts across 436 recent and extinct amniote taxa. Vertebral counts were mapped onto a generalized amniote phylogeny as well as individual ingroup trees, and ancestral states were reconstructed by using squared-change parsimony. We also calculated the relationship between presacral and cervical numbers to infer the relative influence of homeotic effects and meristic changes and found no correlation between somitogenesis and Hox-mediated regionalization. Although conservatism in presacral numbers characterized early synapsid lineages, in some cases reptiles and synapsids exhibit the same developmental innovations in response to similar selective pressures. Conversely, increases in body mass are not coupled with meristic or homeotic changes, but mostly occur in concert with postembryonic somatic growth. Our study highlights the importance of fossils in large-scale investigations of evolutionary developmental processes.
209 citations
TL;DR: The present cladistic analysis found that two corresponding, fundamental divisions of the dorsal pallium were present in captorhinomorph amniotes and were expanded relative to their condition in anamniotes.
202 citations
TL;DR: Lifestyle is inferred to have been terrestrial for the stem‐tetrapod Discosauriscus, the basal synapsid Dimetrodon, the dicynodont therapsid Dicynodon, an unindentified gorgonopsian, and the parareptile Pareiasaurus, which is modelled as being aquatic, but was more likely amphibious.
Abstract: Bone microanatomy appears to track changes in various physiological or ecological properties of the individual or the taxon. Analyses of sections of the tibia of 99 taxa show a highly significant (P
149 citations
TL;DR: In this paper, an asymmetrical cladogram extending from primitive pelycosaurs to morganucodontid mammaliaforms was created and three different methodologies were then used to compare the amount of morphological change between nodes on this cladogram with the minimum missing time interval between each node, as inferred from sister taxon-based ghost lineages.
Abstract: The origin of mammals has been characterized as a gradual process, a claim based primarily on a well-preserved series of extinct nonmammalian synapsids (“mammal-like reptiles”) that span some 200 million years. In contrast to the origin of many other higher taxa, the origin of mammals from within cynodont-grade therapsids is not considered to coincide with a major morphological change, but rather to be simply the culmination of a series of more and more mammal-like transitional forms. To test these assertions, an asymmetrical cladogram extending from primitive “pelycosaurs” to morganucodontid mammaliaforms was created. Three different methodologies were then used to compare the amount of morphological change between nodes on this cladogram with the minimum missing time interval between each node, as inferred from sister taxon-based ghost lineages. In general, a statistically significant positive relationship was found, indicating that greater numbers of derived features tend to be correlated with longer ghost lineages. A significant correlation between the number of accumulated apomorphies and branching events was also found. Although the rate of character change was variable, in no case was a long ghost lineage associated with few apomorphies. These correlations are consistent with the hypothesis that rapid accumulation of derived features occurred relatively infrequently within the synapsid lineage leading toward mammals and that gradual character evolution predominated.
148 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 9 |
| 2020 | 11 |
| 2019 | 11 |
| 2018 | 6 |
| 2017 | 5 |
| 2016 | 4 |