The study by Delsuc et al. (2006) challenges the traditional view that cephalochordates are the closest living relatives of vertebrates, instead suggesting that tunicates (urochordates) are the closest relatives. Using a phylogenomic dataset of 146 nuclear genes from 14 deuterostomes and 24 other slowly evolving species, the authors found strong evidence supporting the grouping of tunicates and vertebrates into a clade named Olfactores. This finding contradicts the classical hypothesis of euchordate monophyly, which groups cephalochordates and vertebrates together. The study also suggests that chordate monophyly is uncertain, as cephalochordates group with echinoderms, though with moderate statistical support. The authors discuss the implications of these findings for understanding the origins of vertebrates, the nature of their last common ancestor, and the interpretation of developmental and genomic studies. They propose a reappraisal of morphological and paleontological data to better understand the early evolution of deuterostomes.The study by Delsuc et al. (2006) challenges the traditional view that cephalochordates are the closest living relatives of vertebrates, instead suggesting that tunicates (urochordates) are the closest relatives. Using a phylogenomic dataset of 146 nuclear genes from 14 deuterostomes and 24 other slowly evolving species, the authors found strong evidence supporting the grouping of tunicates and vertebrates into a clade named Olfactores. This finding contradicts the classical hypothesis of euchordate monophyly, which groups cephalochordates and vertebrates together. The study also suggests that chordate monophyly is uncertain, as cephalochordates group with echinoderms, though with moderate statistical support. The authors discuss the implications of these findings for understanding the origins of vertebrates, the nature of their last common ancestor, and the interpretation of developmental and genomic studies. They propose a reappraisal of morphological and paleontological data to better understand the early evolution of deuterostomes.