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A new genus and species of galeaspid,  Falxcornus liui  gen. et sp. nov., is described from the Xishancun Formation (Lochkovian, Lower Devonian) in Qujing, Yunnan, China. The new taxon displays a suite of diagnostic characters of the Eugaleaspiformes and strikingly resembles the tridensaspids  Tridensaspis  and  Pterogonaspis  in its sickle-like complex of cornual and inner cornual processes, leaf-like inner cornual processes, and median dorsal opening posteriorly placed level with the centre of the orbital opening, but clearly differs from these genera in lacking the rostral process and laterally projecting cornual processes. An extended phylogenetic analysis of the Galeaspida suggests that  Falxcornus, Pterogonaspis  and  Tridensaspis  form a monophyletic group as the family Tridensaspidae, and  Falxcornus  is resolved as sister to  Pterogonaspis  and  Tridensaspis . Therefore,  Falxcornus liui  gen. et sp. nov. now represents the most primitive and oldest known tridensaspid fish. Its subacute rostral margin and sickle-like complex of cornual and inner cornual processes likely represent an intermediate state of these highly specialised rostral and lateral projecting processes, respectively. The recurrent evolution of similar cephalic elaborations within the Galeaspida suggests that some galeaspids could manipulate water ow around their headshields to become active animals with higher manoeuvrability and versatility, similar to osteostracans.

Falxcornus , a new genus of Tridensaspidae (Galeaspida, stem-Gnathostomata) from the Lower Devonian in Qujing, Yunnan, China