Journal of Paleontology, 92(1), 2018, p. 1–2 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.140


New evolutionary and ecological advances in deciphering the Cambrian explosion of animal life


Zhifei Zhang1 and Glenn A. Brock2


1Shaanxi Key Laboratory of Early Life and Environments, State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an, 710069, China ⟨elizf@nwu.edu.cn⟩ 2Department of Biological Sciences andMarine Research Centre,Macquarie University, Sydney, NSW, 2109, Australia ⟨glenn.brock@mq.edu.au⟩


The Cambrian explosion represents the most profound animal diversification event in Earth history. This astonishing evolu- tionary milieu produced arthropods with complex compound eyes (Paterson et al., 2011), burrowing worms (Mángano and Buatois, 2017), and a variety of swift predators that could cap- ture and crush prey with tooth-rimmed jaws (Bicknell and Paterson, 2017). The origin and evolutionary diversification of novel animal body plans led directly to increased ecological complexity, and the roots of present-day biodiversity can be traced back to this half-billion-year-old evolutionary crucible. Alongside familiar living body plans (phyla), there are bizarre Cambrian forms that can be placed in the stem lineages of modern phyla (Budd and Jensen, 2000), allowing us to piece together the macroevolutionary heritage and timing of character trait assembly in many higher groups. The greatest advances in understanding the history of early animal evolution on Earth have been achieved through investigation of exceptionally pre- served biotas (Könservat-Lagerstätten). While the Cambrian fossil record is deeply skewed in favor of shelly fossils, excep- tionally preserved Cambrian Könservat-Lagerstätten, such as Chengjiang, Guanshan, Emu Bay Shale, Kaili, Burgess Shale, and the Lower Ordovician Fezouata Biota, yield a remarkable array of soft-body/tissue information. Exceptional preservation at these sites provides ‘snapshots’ of the anatomy, body organization, neural evolution, feeding modes, and community structures of the earliest animals that inhabited our planet during the Cambrian Period (541–485 Ma). The fossils dealt with in this special issue come from


Laurentian (Greenland and Labrador, Cambrian Stage 4) and middle Cambrian (Series 3) rocks of Utah; East Gondwana (Emu Bay Shale, Cambrian Stage 4) of South Australia; and a series of Könservat-Lagerstätte from China (in ascending order): the Kuanchuangpu Biota (Fortunian Stage), Chengjiang (Stage 3), Guanshan (Stage 4), Kaili (early Stage 5), andWangcun (Paibian Stage) biotas. A systematic examination of fossil assemblages across


Cambrian continents demonstrates that the appearance of metazoans during the early Cambrian is not completely synchronous. In the earliest Cambrian Terreneuvian Series (Fortunian and unnamed Stage 2), the fossils are represented by abundant, mostly millimetric, small shelly fossils (SSFs), most of which belong in the superphylum Lophotrochozoa (e.g., Kouchinsky et al., 2012). Apart from a few contentious Terreneuvian ecdysozoans (Liu et al., 2014; Zhang et al., 2015),


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the body fossil record of ecdysozoans and deuterostomes is very poorly known during this time, potentially the result of a distinct lack of exceptionally preserved faunas in the Terreneuvian (Fortunian and the unnamed Stage 2). However, this taxonomic ‘gap’ has been partially filled with the discovery of exceptionally well-preserved stem group organisms in the Kuanchuanpu Formation (Fortunian Stage, ca. 535Ma) fromNingqiangCounty, southern Shaanxi Province of central China. High diversity and disparity of soft-bodied cnidarians (see Han et al., 2017b) and scalidophoran worms (Zhang et al., 2017) are revealed to com- plement previously reported basal deuterostomes (Han et al., 2017a). The ecological dominance during the Fortunian is largely represented by abundant radiate clades, especially cnidarians and ctenophores, along with an array of tubes or conical fossilsmainly belonging to lophotrochozoans thatmake up a ‘tube world’ sensu Budd and Jackson (2016). During Cambrian Stage 3, ecdysozoans, especially


trilobites, bivalved arthropods, priapulids, and lobopodians, underwent grand diversification, occupying more than 80% of fossil diversity in the Chengjiang fauna of South China. A diversity of deuterostomes, including the earliest-known agna- than Haikouichthys (Shu et al., 2003) and the enigmatic vetuli- colians (Ou et al., 2012), also underwent an explosive radiation as demonstrated by the faunas in the Chengjiang Könservat- Lagerstätte. Hu et al. (2017) reinterpret the enigmatic fossil Malongitubus kuanshanensis Hu, 2005 as a potential hemi- chordate pterobranch. If interpreted correctly, this stretches the lineage of pterobranchs back to the early Cambrian Stage 3, much earlier than previously thought. Utilizing fossil specimens from the middle Cambrian Burgess Shale and the Late Ordovician of Canada, Holmer et al. (2017) restudied the Chengjiang specimens of Kutorgina chengjiangensis Zhang et al., 2007 and determined that there were two apical openings in the earliest calcareous-shelled brachiopods with the apical foramen representing larval attachment subsequently becoming nonfunctional through ontogeny. In the slightly youngerGuanshan fauna (Stage 4), Zeng et al.


(2017) present the first report of a new radiodontan oral cone with a unique combination of anatomical features, shedding new light on the feeding strategy and phylogeny of anomalocaridids. The approximately cotemporary soft-body fossils of priapulids are also documented for the first time in details from the Yanwangbian Formation of southern Shaanxi, along the northern margin of the Yangtze platform (Yang et al., 2017). These fossils, together with

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