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A large phylogenetic tree is a critical component of comparative analyses that examine broad macroevolutionary patterns, such as the tempo and mode of evolution or morphological disparity through time. However, the sample of species included in published phylogenies rarely aligns with the species that researchers wish to examine in comparative analyses. For instance, early synapsid phylogenies often focus on specific subclades, such as pelycosaurs or anomodonts, rather than broadly encompassing all known synapsid lineages, thus hindering analyses that require detailed sampling across synapsid lineages. To address this issue, we generated a time-calibrated meta-phylogeny (‘metatree’) of synapsid species from the Carboniferous through the Eocene (305–34 Ma). The metatree approach uses source character matrices (rather than source trees) and generates complete sets of most parsimonious trees, combining them rather than generating a single consensus tree. We incorporated 269 published morphological character matrices, which includes every non-mammaliaform synapsid character matrix that has ever been published (as of July 2021) and 57 mammaliaform-focused matrices. Due to evolving ideas of relationships and frequent matrix reuse, each of the matrices was weighted according to its publication year and its dependence on ‘parent’ matrices using an established metatree procedure. The metatree approach relies on XML metadata files that reconcile taxon names to valid Paleobiology Database taxa (PBDB). Because the metatree approach utilizes PBDB taxonomy, we vetted the PBDB information and made approximately 500 additions and corrections to taxon information. The resulting metatree includes 2,128 synapsid species, making it one of the largest fossil phylogenies ever produced. Approximately 1600 species are non-mammaliaform synapsids, and the remaining ~525 species are mammaliaforms, including many of the known Mesozoic and early Cenozoic mammaliaforms. The massive taxonomic and temporal breadth of the metatree make it broadly applicable to studies on synapsid macroevolution. The past decade has witnessed a resurgence of research on non-mammaliaform synapsids, and our new, comprehensive metatree provides a rigorous foundation for continuing work on macroevolutionary patterns and processes among the forerunners of mammals.
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Pelycosaurian "lineages": a meta-analysis of three decades of phylogenetic research
Pelycosaur-grade synapsids comprise the first major radiation of Synapsida, and their phylogenetic relationships have been the subject of over three decades of research in a cladistic framework. In this time three major “lineages” of shared character-taxon matrices have been created, each with distinct sets of characters and taxa which have been analyzed using different tree-construction methods. The majority of papers analyzing “pelycosaur” phylogeny belong to one of these research lineages. Papers rarely cross over to another lineage, but occasionally borrow a few characters from other research lineages. This bias in the sources of “pelycosaur” phylogenetic datasets means that there have been fewer truly independent tests of hypothesized relationships within the group than the number of published analyses would suggest, and that our understanding of “pelycosaur” phylogeny may be less certain than is sometimes portrayed. Here, we use a novel method to create a “pelycosaur” metatree to summarize our current understanding of the group's phylogeny. We also perform a bipartite network analysis to describe relationships between individual datasets and to characterize distinct research lineages. The topology of our metatree shows the most similarity to the results of the largest research lineage, reflecting the large contribution those papers made to the underlying dataset. We recover a monophyletic Caseasauria and Eupelycosauria. Relationships within eupelycosaur subclades also generally match previous hypotheses from the largest lineage. However, within Caseasauria, a monophyletic Eothyrididae falls within Caseidae, reflecting the influence of multiple dataset lineages on recent work on the group. The bipartite network analysis confirms the division of datasets into three main lineages. Moreover, the matrices in the older lineages are more conservative, with fewer character additions or deletions, whereas those in the newest lineage are more variable. Our results reveal how scientific practice has influenced our understanding of “pelycosaur” phylogeny, and suggest that the construction of additional, independent datasets will be an important step in further testing conventional wisdom and traditional phylogenetic hypotheses.
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- Award ID(s):
- 1754502
- PAR ID:
- 10088929
- Date Published:
- Journal Name:
- Society of Vertebrate Paleontology Meeting Program and Abstracts
- Page Range / eLocation ID:
- 242
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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