Data from: Tunicates and not cephalochordates are the closest living relatives of vertebrates

Tunicates or urochordates (appendicularians, salps and sea squirts),
cephalochordates (lancelets) and vertebrates (including lamprey and
hagfish) constitute the three extant groups of chordate animals.
Traditionally, cephalochordates are considered as the closest living
relatives of vertebrates, with tunicates representing the earliest
chordate lineage. This view is mainly justified by overall morphological
similarities and an apparently increased complexity in cephalochordates
and vertebrates relative to tunicates. Despite their critical importance
for understanding the origins of vertebrates, phylogenetic studies of
chordate relationships have provided equivocal results. Taking advantage
of the genome sequencing of the appendicularian Oikopleura dioica, we
assembled a phylogenomic data set of 146 nuclear genes (33,800
unambiguously aligned amino acids) from 14 deuterostomes and 24 other
slowly evolving species as an outgroup. Here we show that phylogenetic
analyses of this data set provide compelling evidence that tunicates, and
not cephalochordates, represent the closest living relatives of
vertebrates. Chordate monophyly remains uncertain because
cephalochordates, albeit with a non-significant statistical support,
surprisingly grouped with echinoderms, a hypothesis that needs to be
tested with additional data. This new phylogenetic scheme prompts a
reappraisal of both morphological and palaeontological data and has
important implications for the interpretation of developmental and genomic
studies in which tunicates and cephalochordates are used as model animals.