Three-dimensional morphology of the biramous appendages in Isoxys from the early Cambrian of South China, and its implications for early euarthropod evolution
Creators: name: Zhang, Caixia
name: Liu, Yu
name: Javier, Ortega-Hernández
name: Zhai, Dayou
name: Wolfe, Joanna
name: Hou, Xianguang
name: Mai, Huijuan
name: Jin, Changfei
name: Guo, Jin
Publisher: name: Zenodo
Year: 2023
Subjects: the early Cambrian Chengjiang biota
early euarthropod evolution
appendage differentiation
arthrodization and arthropodization
isoxys
micro-computed tomography

description: Early euarthropod evolution involved a major transition from lobopodian-like taxa to organisms featuring a segmented, well-sclerotized trunk (arthrodization) and limbs (arthropodization). However, the precise origin of a completely arthrodized trunk and arthropodized ventral biramous appendages remain controversial, as well as the early onset of anterior-posterior limb differentiation in stem-group euarthropods. New fossil material and micro-computed tomography inform the detailed morphology of the arthropodized biramous appendages in the carapace-bearing euarthropod <em>Isoxys curvirostratus </em>from the early Cambrian Chengjiang biota. In addition to well-developed grasping frontal appendages. <em>I. curvirostratus</em> possesses two batches of morphologically and functionally distinct biramous limbs. The first batch consists of four pairs of short cephalic appendages with robust endites with a feeding function, whereas the second batch has more elongate trunk appendages for locomotion. Critically, our new material shows that the trunk of <em>I. curvirostratus</em> was not arthrodized. The results of our phylogenetic analyses recover isoxyids as some of the earliest branching sclerotized euarthropods, and strenghens the hypothesis that arthropodized biramous appendage evolved before full body arthrodization.
description: Nexus (.nex) is a common file type for phylogenetic data, and the required runfile to use MrBayes for phylogenetic analysis. .p are sampled parameter files from MrBayes analysis, output for each run specigied. Newick (.tre) files are phylogenetic tree outputs, which can be visualized directly e.g. with Figtree. .tnt is a file type for phylogenetic data, specifically the required runfile to conduct maximum parsimony phylogenetic analysis in TNT.Funding provided by: Yunnan Provincial Science and Technology Department<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100008871<br>Award Number: YNWR-QNBJ-2019-295, 202101AT070158, 2019DG050, and 2015HC029Funding provided by: National Natural Science Foundation of China<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100001809<br>Award Number: 41861134032Funding provided by: National Science Foundation<br>Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000001<br>Award Number: DEB #1856679Funding provided by: Harvard China Fund **<br>Crossref Funder Registry ID: <br>Award Number: 41861134032
description: Anatomical data are collected by photos from a Keyence VHX 6000 and Leica M205AF stereomicroscope, a GE Phoenix Nanotom cone beam scanner and a Zeiss Xradia 520 Versa X-ray microscope. And we analysed it in MrBayes v.3.2.7.