Tunicates, not cephalochordates, are the closest living relatives of vertebrates, according to a study by Frédéric Delsuc, Henner Brinkmann, Daniel Chourrout, and Hervé Philippe. Using genome sequencing of the appendicularian Oikopleura dioica, the researchers analyzed 146 nuclear genes from 14 deuterostomes and 24 other slowly evolving species. Their phylogenomic dataset provided strong evidence that tunicates are the closest relatives of vertebrates, not cephalochordates. The study also found that chordate monophyly remains uncertain, as cephalochordates may group with echinoderms, a hypothesis requiring further testing. The results challenge the traditional view that cephalochordates are the closest relatives of vertebrates and suggest that tunicates and vertebrates form a clade called Olfactores. The study also highlights the importance of molecular data in phylogenetic analysis and the need for further research to resolve the evolutionary relationships among deuterostomes. The findings have implications for understanding the origins of vertebrates and the evolution of developmental and genomic features. The study used multiple phylogenetic methods, including maximum likelihood, Bayesian inference, and maximum parsimony, to analyze the data and support the conclusion that tunicates are the closest relatives of vertebrates. The results suggest that the traditional textbook view of chordate evolution is incorrect and that tunicates should no longer be considered primitive but rather derived chordates with specialized lifestyles. The study also emphasizes the importance of considering systematic biases, such as long-branch attraction, in phylogenetic analysis. The findings have significant implications for the interpretation of developmental and genomic studies using tunicates and cephalochordates as model organisms.Tunicates, not cephalochordates, are the closest living relatives of vertebrates, according to a study by Frédéric Delsuc, Henner Brinkmann, Daniel Chourrout, and Hervé Philippe. Using genome sequencing of the appendicularian Oikopleura dioica, the researchers analyzed 146 nuclear genes from 14 deuterostomes and 24 other slowly evolving species. Their phylogenomic dataset provided strong evidence that tunicates are the closest relatives of vertebrates, not cephalochordates. The study also found that chordate monophyly remains uncertain, as cephalochordates may group with echinoderms, a hypothesis requiring further testing. The results challenge the traditional view that cephalochordates are the closest relatives of vertebrates and suggest that tunicates and vertebrates form a clade called Olfactores. The study also highlights the importance of molecular data in phylogenetic analysis and the need for further research to resolve the evolutionary relationships among deuterostomes. The findings have implications for understanding the origins of vertebrates and the evolution of developmental and genomic features. The study used multiple phylogenetic methods, including maximum likelihood, Bayesian inference, and maximum parsimony, to analyze the data and support the conclusion that tunicates are the closest relatives of vertebrates. The results suggest that the traditional textbook view of chordate evolution is incorrect and that tunicates should no longer be considered primitive but rather derived chordates with specialized lifestyles. The study also emphasizes the importance of considering systematic biases, such as long-branch attraction, in phylogenetic analysis. The findings have significant implications for the interpretation of developmental and genomic studies using tunicates and cephalochordates as model organisms.