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Liu C, Fu D, Wu Y, Zhang X. Cambrian euarthropod Urokodia aequalis sheds light on the origin of Artiopoda body plan. iScience 2024; 27:110443. [PMID: 39148713 PMCID: PMC11325232 DOI: 10.1016/j.isci.2024.110443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2024] [Revised: 05/22/2024] [Accepted: 07/01/2024] [Indexed: 08/17/2024] Open
Abstract
The origin and evolution of trilobated body plan of the Artiopoda, a group of epibenthic euarthropods from Cambrian Lagerstätten, remain unclear. Here we examine old and new specimens of Urokodia aequalis, one of euarthropods from the Chengjiang biota, revealing new morphological details and revising its taxonomy. Urokodia possesses an elongate body with a five-segmented head, a thorax with 13-15 tergites, and a three-segmented pygidium with well-defined axial region. The ventral morphology includes paired stalked eyes, one fleshy antenna pair, the following homogeneous head and thoracic appendages, each with an annular proximal-element, an articulated stenopodous branch and a lamellar flap, and the pygidial appendages solely consisting of lamellar flaps. Cladistic analyses resolved Urokodia as the basal-most member of the Artiopoda, offering a hypothesis of the initial origin of trilobation in the pygidium. The new data, in conjunction with the presence of the elongated body plan across major lineages of euarthropods, suggest a convergent evolution of this trait.
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Affiliation(s)
- Cong Liu
- State Key Laboratory of the Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi'an 710069, China
| | - Dongjing Fu
- State Key Laboratory of the Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi'an 710069, China
| | - Yu Wu
- State Key Laboratory of the Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi'an 710069, China
| | - Xingliang Zhang
- State Key Laboratory of the Continental Dynamics, Shaanxi Key Laboratory of Early Life and Environments, Department of Geology, Northwest University, Xi'an 710069, China
- Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China
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Park TYS. Trilobite hypostome as a fusion of anterior sclerite and labrum. ARTHROPOD STRUCTURE & DEVELOPMENT 2023; 77:101308. [PMID: 37832459 DOI: 10.1016/j.asd.2023.101308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Revised: 09/13/2023] [Accepted: 09/20/2023] [Indexed: 10/15/2023]
Abstract
The trilobite hypostome is a biomineralized ventral plate that covers the mouth, but its evolutionary origin remains controversial. The labrum is a lobe-like structure that can take on variety of shapes in front of the mouth in arthropods, while the anterior sclerite refers to a cuticular plate articulated to the anterior margin of the head in some Cambrian arthropods. Here I present a perspective that views the trilobite hypostome as a fusion of the anterior sclerite and the labrum based on anatomical, topological, and developmental evidence. According to this perspective, the anterior lobe of the hypostome originated from the anterior sclerite, while the posterior lobe reflects a remnant of the sclerotized cover of the labrum. The convex anterior lobe housed the root of the eye stalks, represented by the palpebral ridges and the hypostomal wing, and the posterior lobe occasionally developed a pair of posterolateral extensions, as do the labra. The position of the antennal insertion was located in front of the posterior lobe, displaying a similar topology to the Cambrian arthropods with the labrum. The hypostome was present in many artiopodans except for the Conciliterga, in which the anterior sclerite was separate from the labrum.
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Affiliation(s)
- Tae-Yoon S Park
- Division of Earth Sciences, Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon, 21990, Republic of Korea; Polar Science, University of Science & Technology, 217 Gajeong-ro, Yuseong-gu, 34113, Daejeon, Republic of Korea.
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Schmidt M, Hou X, Zhai D, Mai H, Belojević J, Chen X, Melzer RR, Ortega-Hernández J, Liu Y. Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods. Philos Trans R Soc Lond B Biol Sci 2022; 377:20210030. [PMID: 35125003 PMCID: PMC8819370 DOI: 10.1098/rstb.2021.0030] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The Cambrian Stage 3 Chengjiang biota in South China is one of the most influential Konservat-Lagerstätten worldwide thanks to the fossilization of diverse non-biomineralizing organisms through pyritization. Despite their contributions to understanding the evolution of early animals, several Chengjiang species remain poorly known owing to their scarcity and/or incomplete preservation. Here, we use micro-computed tomography to reveal in detail the ventral appendage organization of the enigmatic non-trilobite artiopod Pygmaclypeatus daziensis-one of the rarest euarthropods in Chengjiang-and explore its functional ecology and broader evolutionary significance. Pygmaclypeatus daziensis possesses a set of uniramous antennae and 14 pairs of post-antennal biramous appendages, the latter of which show an unexpectedly high degree of heteronomy based on the localized differentiation of the protopodite, endopodite and exopodite along with the antero-posterior body axis. The small body size (less than 2 cm), the presence of delicate spinose endites and well-developed exopodites with multiple paddle-shaped lamellae on the appendages of P. daziensis indicate a nekto-benthic mode of life and a scavenging/detritus feeding strategy. Pygmaclypeatus daziensis shows that appendage heteronomy is phylogenetically widespread within Artiopoda-the megadiverse clade that includes trilobites and their relatives with non-biomineralizing exoskeletons-and suggests that a single exopodite lobe with paddle-like lamellae is ancestral for this clade. This article is part of the theme issue 'The impact of Chinese palaeontology on evolutionary research'.
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Affiliation(s)
- Michel Schmidt
- MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China.,Bavarian State Collection of Zoology, Bavarian Natural History Collections, Münchhausenstrasse 21, 81247 München, Germany.,Department Biology II, Ludwig-Maximilians-Universität München, 82152 Planegg-Martinsried, Germany
| | - Xianguang Hou
- MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China.,Yunnan Key Laboratory for Palaeobiology, Institute of Palaeontology, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China
| | - Dayou Zhai
- MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China.,Yunnan Key Laboratory for Palaeobiology, Institute of Palaeontology, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China
| | - Huijuan Mai
- MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China.,Yunnan Key Laboratory for Palaeobiology, Institute of Palaeontology, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China
| | - Jelena Belojević
- Bavarian State Collection of Zoology, Bavarian Natural History Collections, Münchhausenstrasse 21, 81247 München, Germany
| | - Xiaohan Chen
- MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China.,Yunnan Key Laboratory for Palaeobiology, Institute of Palaeontology, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China
| | - Roland R Melzer
- MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China.,Bavarian State Collection of Zoology, Bavarian Natural History Collections, Münchhausenstrasse 21, 81247 München, Germany.,Department Biology II, Ludwig-Maximilians-Universität München, 82152 Planegg-Martinsried, Germany.,GeoBio-Center, Ludwig-Maximilians-Universität Munich, Luisenstrasse 37, 80333 München, Germany
| | - Javier Ortega-Hernández
- Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, 791 Cambridge, MA 02138, USA
| | - Yu Liu
- MEC International Joint Laboratory for Palaeobiology and Palaeoenvironment, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China.,Yunnan Key Laboratory for Palaeobiology, Institute of Palaeontology, Yunnan University, North Cuihu Road 2, Kunming 650091, People's Republic of China
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Dzik J. Protaspis larva of an aglaspidid-like arthropod from the Ordovician of Siberia and its habitat. ARTHROPOD STRUCTURE & DEVELOPMENT 2021; 61:101026. [PMID: 33508709 DOI: 10.1016/j.asd.2020.101026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 12/30/2020] [Accepted: 12/30/2020] [Indexed: 06/12/2023]
Abstract
A fossil larva lacking segmentation of the calcified carapace, closely resembling the trilobite protaspis, has been found associated with other skeletal elements of an angarocaridid Girardevia species in the mid Darriwilian of central Siberia. The presence of protaspis larvae in the angarocaridids, generally believed to represent a branch of the Aglaspidida, supports their proximity to trilobites and proves a low position on the arthropod phylogenetic tree but does not necessarily contradict the chelicerate affinity. The cephalic appendages of angarocaridids bore massive gnathobases with detachable spines, closely similar to those known in extant xiphosurans and in their probable Cambrian relatives. The stratigraphic succession of the angarocaridids, their phosphatized cuticle pieces being abundant in the Ordovician strata of Siberia, shows a gradual improvement of mechanical resistance of their carapaces, eventually resulting in a honeycomb structure. The associated benthic mollusc assemblage is dominated with the bellerophontids showing high mortality at metamorphosis and only the limpet-like Pterotheca, infaunal bivalves, and scaphopods being able to survive this in a substantial number. This suggests a strong selective pressure from predators equipped with well-skeletonised oral apparatuses able to crush mineralized body covers of their prey. Possibly, these were some of the associated conodonts of appropriate size and co-evolving towards their ability to crush more and more resistant cuticle. Less likely candidates for durophagy are endoceratid or orthoceratid cephalopods. Also the angarocaridids themselves, equipped with robust gnathobases of cephalic appendages, apparently predated on benthic shelly animals.
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Affiliation(s)
- Jerzy Dzik
- Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland; Institute of Evolutionary Biology, Faculty of Biology, Biological and Chemical Research Centre (CNBCh UW), University of Warsaw, Warszawa, 02-089 Żwirki i Wigury 101, Poland.
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