Abstract: The earliest record of dentine, an early vertebrate novelty, has been controversially represented by Anatolepis heintzi, known from fragmentary Cambrian and Ordovician fossils. With exoskeletons having the characteristic tubules of dentine, it was argued that Anatolepis demonstrated the first precursors of teeth, known as odontodes. Debates whether Anatolepis is a vertebrate have arisen largely because of limitations in imaging and the lack of comparative exoskeletal tissues. To resolve this controversy, and understand the origin of dental tissues, we synchrotron scanned diverse extinct and extant vertebrate and invertebrate exoskeletons. We find that the tubules of Anatolepis have been misidentified as dentine and instead are definitively sensory sensilla components of aglaspidid arthropods. External odontodes of Eriptychius, an Ordovician taxon with true vertebrate apomorphies, have remarkably large dentin tubules1 that are morphologically convergent with invertebrate sensilla. Using immunofluorescence, we show that the external odontodes of extant chondrichthyans and teleosts retain extensive innervation suggestive of a sensory function like that in teeth. These patterns of convergence and innervation reveal that dentine arose as a sensory tissue in the exoskeleton of early vertebrates, a function retained in modern vertebrate teeth. Moreover, Middle Ordovician fossils now represent the oldest known vertebrate dental tissues