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Reproduction in jawed vertebrates (gnathostomes) involves either external or internal fertilization (1). It is commonly argued that internal fertilization can evolve from external, but not the reverse. Male copulatory claspers are present in certain placoderms (2-4), fossil jawed vertebrates retrieved as a paraphyletic segment of the gnathostome stem group in recent studies (5-8). This suggests that internal fertilization could be primitive for gnathostomes, but such a conclusion depends on demonstrating that copulation was not just a specialized feature of certain placoderm subgroups. The reproductive biology of antiarchs, consistently identified as the least crownward placoderms (5-8) and thus of great interest in this context, has until now remained unknown. Here we show that certain antiarchs possessed dermal claspers in the males, while females bore paired dermal plates inferred to have facilitated copulation. These structures are not associated with pelvic fins. The clasper morphology resembles that of ptyctodonts, a more crownward placoderm group (7 8), suggesting that all placoderm claspers are homologous and that internal fertilization characterized all placoderms. This implies that external fertilization and spawning, which characterize most extant aquatic gnathostomes, must be derived from internal fertilization, even though this transformation has been thought implausible. Alternatively, the substantial morphological evidence for placoderm paraphyly must be rejected., Among living fish (non-tetrapod vertebrates) internal fertilization is mostly effected by copulatory structures representing modifications of the pelvic fins (chondrichthyans (9)) or anal fins (the gonopodium of some teleost fishes [...]

Teeth and jaws constitute a model of the evolutionary developmental biology concept of modularity (1) and they have been considered the key innovations underpinning a classic example of adaptive radiation [...]

Evidence of reproductive biology is extremely rare in the fossil record. Recently the first known embryos were discovered within the Placodermi (1), an extinct class of armoured fish, indicating a [...]

Letter to the Editor, Author(s): Paul M. Barrett, Zerina Johanson Author Affiliations: Myanmar amber fossils: a legal as well as ethical quagmire The ethical status of fossil material in Myanmar amber is one of [...]

Rhizodonts are more distant from tetrapods than are osteolepiform and elpistostegid lobefin fishes, according to research based on the discovery from the Upper Devonian period of Canowindra, Australia, of the most primitive and most complete rhizodont ever discovered. This specimen, designated Gooloogongia loomesi sp. nov., indicates that rhizodonts have a single external nostril. However, there are no other tetrapod-like features. It can be concluded that the similarities between the pectoral appendage skeletons of rhizodonts and tetrapods are convergent.