| 论文摘要 |
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. |
