Redescription ofPhymolepis cuifengshanensis(Antiarcha: Yunnanolepididae) using high-resolution computed tomography and new insights into anatomical details of the endocranium in antiarchs

Abstract

BackgroundYunnanolepidoids constitute either the most basal consecutive segments or the most primitive clade of antiarchs, a highly diversified jawed vertebrate group from the Silurian and Early Devonian periods. Although the general morphology of yunnanolepidoids is well established, their endocranial features remain largely unclear, thus hindering our further understanding of antiarch evolution, and early gnathostome evolution. Phymolepis cuifengshanensis, a yunnanolepidoid from the Early Devonian of southwestern China, is re-described in detail to reveal the information on endocranial anatomy and additional morphological data of head and trunk shields.MethodsWe scanned the material of P. cuifengshanensis using high-resolution computed tomography and generated virtual restorations to show the internal morphology of its dermal shield. The dorsal aspect of endocranium in P. cuifengshanensis was therefore inferred. The phylogenetic analysis of antiarchs was conducted based on a revised and expanded dataset that incorporates 10 new cranial characters.ResultsThe lateroventral fossa of trunk shield and Chang’s apparatus are three-dimensionally restored in P. cuifengshanensis. The canal that is positioned just anterior to the internal cavity of Chang’s apparatus probably corresponds to the rostrocaudal canal of euantiarchs. The endocranial morphology of P. cuifengshanensis corroborates a general pattern for yunnanolepidoids with additional characters distinguishing them from sinolepids and euantiarchs, such as a developed cranio-spinal process, an elongated endolymphatic duct, and a long occipital portion.DiscussionIn light of new data from Phymolepis and Yunnanolepis, we summarized the morphology on the visceral surface of head shield in antiarchs, and formulated an additional 10 characters for the phylogenetic analysis. These cranial characters exhibit a high degree of morphological disparity between major subgroups of antiarchs, and highlight the endocranial character evolution in antiarchs.

Feeding in the Devonian antiarch placoderm fishes: a study based upon morphofunctional analysis of jaws

“…With respect to feeding modes, the cartilaginous branchial arches themselves are not preserved; nevertheless, some consideration of the space in which these were held (and so size and potential complexity of the apparatus) can be made. In yunnanolepids, the anterior transverse crista, located on the visceral surface of the anterior ventral trunk shield, occurs along with an ornamented postbranchial lamina (e.g., Wang and Zhu, 2018). This ornamented lamina is located at the rostral margin of the trunk shield, marking the rear of the branchial cavity, comparable to the mesially directed and ornamented flange of the pectoral girdle in actinopterygians such as Acipenser (Jessen, 1972, fig.…”

Reappraisal of the Silurian placodermSilurolepisand insights into the dermal neck joint evolution

“…Essentially, nearly identical conditions occur in Qilinyu and Silurolepis , in which the posterior flange of the skull roof inserts into the slot-shaped articular fossa on the trunk shield. The paired ventral articular lamina in antiarchs, named ‘subarticular ridge’ [46], forms the ventral aspect of the slot-shaped fossa and should be homologous to the articular lamina in Qilinyu, Silurolepis and most other placoderms. Although in antiarchs the ventral surface of the skull roof does not bear a fossa as in the dual articulation of Qilinyu , the articular fossa on the trunk shield, a continuous flange on the posterior margin of the skull roof acting like articulation lamina and the cuboid trunk shield incorporating multiple MD plates, are still only shared in antiarchs, Qilinyu and Silurolepis .…”

Asia–Gondwana connections indicated by Devonian fishes from Australia: palaeogeographic considerations

“…Recently, Pan et al (2017) suggested that Luquanolepis (Emsian, Yunnan Province) could belong in this group (previously interpreted as a probable bothriolepid; Zhang and Young 1992). However the skull of Luquanolepis is not known, so this result is very provisional (and not supported in the analysis of Wang and Zhu 2018). Asterolepid affinity is anomalous given that all other Chinese antiarchs (except Hunanolepis, Remigolepis) are yunnanolepids, bothriolepids, or sinolepids.…”

“…Zhao and Zhu 2007) represents one of the most dramatic endemic radiations in vertebrate evolutionary history. Of over 40 antiarch genera recognised in the most recent phylogenetic analysis, eight genera are yunnanolepids (Wang and Zhu 2018). This highly endemic group is only known from Asia.…”