Phylogenomic Reconstruction of Ancient Vertebrates

Abstract

Deep vertebrate phylogenomics has historically been hindered by long-branch attraction, incomplete lineage sorting, and the difficulty of aligning orthologous regions across highly divergent taxa spanning over 500 million years of evolutionary history. This study assembled a phylogenomic dataset of 2,840 ultraconserved element (UCE) loci and 384 single-copy nuclear gene families from 84 vertebrate taxa representing all major clades -- including jawless vertebrates (Petromyzontida, Myxini), cartilaginous fishes (Chondrichthyes), ray-finned fishes (Actinopterygii), lobe-finned fishes (Coelacanthimorpha, Dipnoi), and all tetrapod orders -- supplemented with 12 newly sequenced whole genomes from taxonomically critical lineages. Concatenated maximum likelihood analysis (IQ-TREE; 2,840 UCE supermatrix, 4,284,840 aligned bp) and coalescent-based species tree estimation (ASTRAL-III; 2,840 gene trees) produced largely congruent topologies resolving 94.8% of nodes with bootstrap support >= 95%. Key results include: confirmation of Cyclostomata monophyly (lamprey + hagfish; bootstrap 98%), resolution of Coelacanthimorpha as sister to the Tetrapoda + Dipnoi clade (bootstrap 96%), placement of turtles as sister to Archosauria (bootstrap 99%), and divergence time estimates placing the Gnathostomata origin at 484 +/- 12 Ma and the Tetrapoda origin at 384 +/- 8 Ma. Twelve nodes previously unresolved or conflicted across published phylogenies were resolved with strong support, and concordance factor analysis identified six lineages with significant incomplete lineage sorting that explains previous topological conflicts. These results provide the most comprehensive and robustly supported vertebrate phylogeny to date, with direct applications to comparative genomics, macroevolutionary analysis, and vertebrate taxonomy.