Evidence for gill slits and a pharynx in Cambrian vetulicolians: implications for the early evolution of deuterostomes

BMC Biology

Research Article

Ailin Chen¹  Simon Conway Morris²  Qiang Ou³  Degan Shu⁴  Jianni Liu⁵  Zhifei Zhang⁵  Xingliang Zhang⁵  Jian Han⁵ 

[1] Chengjiang Fauna National Geopark of China, 652500, Chengjiang, China;Department of Earth Sciences, University of Cambridge, Downing Street, CB2 3EQ, Cambridge, UK;Early Life Evolution Laboratory, School of Earth Sciences and Resources, China University of Geosciences, 100083, Beijing, China;Early Life Evolution Laboratory, School of Earth Sciences and Resources, China University of Geosciences, 100083, Beijing, China;Early Life Institute and Key Laboratory of Continental Dynamics, Northwest University, 710069, Xi'an, China;Early Life Institute and Key Laboratory of Continental Dynamics, Northwest University, 710069, Xi'an, China;

关键词: Ventral Midline;    Suspension Feeding;    Gill Slit;    Pharyngeal Cavity;    Branchial Chamber;   

DOI  :  10.1186/1741-7007-10-81

 received in 2012-06-05, accepted in 2012-10-02,  发布年份 2012

来源: Springer

【 摘 要 】

BackgroundVetulicolians are a group of Cambrian metazoans whose distinctive bodyplan continues to present a major phylogenetic challenge. Thus, we see vetulicolians assigned to groups as disparate as deuterostomes and ecdysozoans. This divergence of opinions revolves around a strikingly arthropod-like body, but one that also bears complex lateral structures on its anterior section interpreted as pharyngeal openings. Establishing the homology of these structures is central to resolving where vetulicolians sit in metazoan phylogeny.ResultsNew material from the Chengjiang Lagerstätte helps to resolve this issue. Here, we demonstrate that these controversial structures comprise grooves with a series of openings. The latter are oval in shape and associated with a complex anatomy consistent with control of their opening and closure. Remains of what we interpret to be a musculature, combined with the capacity for the grooves to contract, indicate vetulicolians possessed a pumping mechanism that could process considerable volumes of seawater. Our observations suggest that food captured in the anterior cavity was transported to dorsal and ventral gutters, which then channeled material to the intestine. This arrangement appears to find no counterpart in any known fossil or extant arthropod (or any other ecdysozoan). Anterior lateral perforations, however, are diagnostic of deuterostomes.ConclusionsIf the evidence is against vetulicolians belonging to one or other group of ecdysozoan, then two phylogenetic options seem to remain. The first is that such features as vetulicolians possess are indicative of either a position among the bilaterians or deuterostomes but apart from the observation that they themselves form a distinctive and recognizable clade current evidence can permit no greater precision as to their phylogenetic placement. We argue that this is too pessimistic a view, and conclude that evidence points towards vetulicolians being members of the stem-group deuterostomes; a group best known as the chordates (amphioxus, tunicates, vertebrates), but also including the ambulacrarians (echinoderms, hemichordates), and xenoturbellids. If the latter, first they demonstrate that these members of the stem group show few similarities to the descendant crown group representatives. Second, of the key innovations that underpinned deuterostome success, the earliest and arguably most seminal was the evolution of openings that define the pharyngeal gill slits of hemichordates (and some extinct echinoderms) and chordates.

【 授权许可】

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© Ou et al; licensee BioMed Central Ltd. 2012. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.