One of the major transitions in vertebrate history was the evolution of jawed vertebrates from their jawless ancestors. Jawed vertebrates account for over 99% of living vertebrates and comprise two groups, cartilaginous fishes and bony fishes, so named for their skeletons. In contrast, living jawless fishes comprise just the parasitic hagfish and the scavenging lamprey, totaling around 100 species. In addition to their eponymous jaws and teeth, jawed fishes possess a number of anatomical innovations such as paired appendages, bony tissues, and three semicircular canals in the inner ear. ‘Placoderms’, the closest fossil relatives of living jawed vertebrates, occupy a critical place in understanding the origins of jawed vertebrates but the anatomy and relationships of placoderms, and even whether they represent a natural group, remains contentious. Recent work employing micro-computed tomography (CT scanning) of both newly-discovered and long-known fossils has revealed previously unknown structures in the braincase, a bony ‘box’ that sits inside the skull and houses the brain, and in the bony labyrinth, which acts as an organ of balance, including features seen in both fossil jawless fishes and living jawed fishes. CT-based studies have also identified unexpected instances of extensive dermal and endochondral bone in the earliest jawed fishes. This implies radical revisions to accepted hypotheses of skeletal tissue evolution, turning on its head the idea that chondrichthyans (sharks, rays and skates) represent a ‘primitive’ vertebrate radiation. Fundamentally, current hypotheses of relationships for ‘placoderms’ are far from stable and likely inaccurate, with major repercussions for the pattern of evolution at the origin of jaws.