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

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1 Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China
2 CAS Center for Excellence in Life and Paleoenvironment, Beijing, China
3 University of Chinese Academy of Sciences, Beijing, China
DOI
10.7287/peerj.preprints.26867v1
Published
Accepted
Subject Areas
Evolutionary Studies, Paleontology, Zoology
Keywords
Devonian, gnathostomes, placoderms, CT scanning, phylogeny, endocranial morphology, antiarchs, anatomy
Copyright
© 2018 Wang et al.
Licence
This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
Cite this article
Wang Y, Zhu M. 2018. Redescription of Phymolepis cuifengshanensis (Antiarcha: Yunnanolepididae) using high-resolution computed tomography and new insights into anatomical details of the endocranium in antiarchs. PeerJ Preprints 6:e26867v1

Abstract

Background. Yunnanolepidoids constitute either the basal-most 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.

Methods. We scanned the material of P. cuifengshanensis using high-resolution computed tomography a nd 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 ten new cranial characters.

Results. The lateroventral fossa of trunk shield and Chang’s apparatus arethree-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.

Discussion. In light of new data from Phymolepis and Yunnanolepis, we summarized the morphology on the visceral surface of head shield in antiarchs, and formulated additional ten 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.

Author Comment

This is a submission to PeerJ for review.

Supplemental Information

Supplementary text

Phylogenetic analysis: (1) Character list. (2) Taxa and principal sources of data. (3) Data matrix with 79 morphological characters for 44 taxa. (4) Characters and character states defining major clades shown in Supplementary Figure 1. (5) Supplementary references.

DOI: 10.7287/peerj.preprints.26867v1/supp-1

Character matrix of antiarchs

Nexus file comprising 44 taxa and 78 morphological characters.

DOI: 10.7287/peerj.preprints.26867v1/supp-2

Supplementary figure to show character transformations in antiarchs

Unambiguous character state changes mapped across one of the most parsimonious trees (Figure 14).

DOI: 10.7287/peerj.preprints.26867v1/supp-3

Phymolepis cuifengshanensis (IVPP V4425.2) based on high-resolution CT

Continuous transverse sections of the specimen.

DOI: 10.7287/peerj.preprints.26867v1/supp-4

Head and trunk shields of Phymolepis cuifengshanensis

Three-dimensional model of IVPP V4425.2.

DOI: 10.7287/peerj.preprints.26867v1/supp-5

Head shield of Phymolepis cuifengshanensis (IVPP V4425.2) based on high-resolution CT

Three-dimensional semi-transparent model to show the cavities and endolymphatic ducts within the dermal shield.

DOI: 10.7287/peerj.preprints.26867v1/supp-6