Pei-yun Cong

Arthropod eyes: The early Cambrian fossil record and divergent evolution of visual systems

Four types of eyes serve the visual neuropils of extant arthropods: compound retinas composed of adjacent facets; a visual surface populated by spaced eyelets; a smooth transparent cuticle providing inwardly directed lens cylinders; and single-lens eyes. The first type is a characteristic of pancrustaceans, the eyes of which comprise lenses arranged as hexagonal or rectilinear arrays, each lens crowning 8-9 photoreceptor neurons. Except for Scutigeromorpha, the second type typifies Myriapoda whose relatively large eyelets surmount numerous photoreceptive rhabdoms stacked together as tiers. Scutigeromorph eyes are facetted, each lens crowning some dozen photoreceptor neurons of a modified apposition-type eye. Extant chelicerate eyes are single-lensed except in xiphosurans, whose lateral eyes comprise a cuticle with a smooth outer surface and an inner one providing regular arrays of lens cylinders. This account discusses whether these disparate eye types speak for or against divergence from one ancestral eye type. Previous considerations of eye evolution, focusing on the eyes of trilobites and on facet proliferation in xiphosurans and myriapods, have proposed that the mode of development of eyes in those taxa is distinct from that of pancrustaceans and is the plesiomorphic condition from which facetted eyes have evolved. But the recent discovery of enormous regularly facetted compound eyes belonging to early Cambrian radiodontans suggests that high-resolution facetted eyes with superior optics may be the ground pattern organization for arthropods, predating the evolution of arthrodization and jointed post-protocerebral appendages. Here we provide evidence that compound eye organization in stem-group euarthropods of the Cambrian can be understood in terms of eye morphologies diverging from this ancestral radiodontan-type ground pattern. We show that in certain Cambrian groups apposition eyes relate to fixed or mobile eyestalks, whereas other groups reveal concomitant evolution of sessile eyes equipped with optics typical of extant xiphosurans. Observations of fossil material, including that of trilobites and eurypterids, support the proposition that the ancestral compound eye was the apposition type. Cambrian arthropods include possible precursors of mandibulate eyes. The latter are the modified compound eyes, now sessile, and their underlying optic lobes exemplified by scutigeromorph chilopods, and the mobile stalked compound eyes and more elaborate optic lobes typifying Pancrustacea. Radical divergence from an ancestral apposition type is demonstrated by the evolution of chelicerate eyes, from doublet sessile-eyed stem-group taxa to special apposition eyes of xiphosurans, the compound eyes of eurypterids, and single-lens eyes of arachnids. Different eye types are discussed with respect to possible modes of life of the extinct species that possessed them, comparing these to extant counterparts and the types of visual centers the eyes might have served.

An exceptionally preserved arthropod cardiovascular system from the early Cambrian

The assumption that amongst internal organs of early arthropods only the digestive system withstands fossilization is challenged by the identification of brain and ganglia in early Cambrian fuxianhuiids and megacheirans from southwest China. Here we document in the 520-million-year-old Chengjiang arthropod Fuxianhuia protensa an exceptionally preserved bilaterally symmetrical organ system corresponding to the vascular system of extant arthropods. Preserved primarily as carbon, this system includes a broad dorsal vessel extending through the thorax to the brain where anastomosing branches overlap brain segments and supply the eyes and antennae. The dorsal vessel provides segmentally paired branches to lateral vessels, an arthropod ground pattern character, and extends into the anterior part of the abdomen. The addition of its vascular system to documented digestive and nervous systems resolves the internal organization of F. protensa as the most completely understood of any Cambrian arthropod, emphasizing complexity that had evolved by the early Cambrian.

Palaeogene fossil Populus leaves from Lanzhou Basin and their palaeoclimatic significance

An angiosperm compression flora is found in Palaeogene from Lanzhou Basin and the cuticular analysis of Populus davidiana Dode in the flora is carefully made. Furthermore, the fossil cuticles are compared with the epidermal structures of extant Populus leaves growing in different environments, i.e. moist, semimoist, and semiarid to arid climatic regions. The present experiments indicate that mature leaves of P. davidiana show leaf size from big to small, leaf cuticles from thick to thin and anticlinal walls of epidermal cells from faintness to clarity along with the increase of latitudes of the plant distributions, the climatic variation from moist to arid, the annual precipitation from more to less and the annual mean temperature from high to low. The fossil P. davidiana differs from the specimens collected from Shandan in semiarid to arid climatic regions but closely resembles the Wushan leaves in a semi-moist climatic area in a lot of features. In a word, the new research may reflect that the flora lives in a semi-moist climatic environment. The present discovery of compression of Paleogene Populus davidiana is of great significance to studying vegetation types, climatic and environmental changes during the primal uplifting of the Qinghai-Tibet Plateau.

Morphology of the radiodontan Lyrarapax from the early Cambrian Chengjiang biota

Abstract. The recently described radiodontan Lyrarapax unguispinus Cong et al., 2014 from the Chengjiang biota (Cambrian Series 2, Stage 3) highlighted a new morphological type of frontal appendage and unique mouth structures, a functional combination reinforcing the diversification of feeding strategies of radiodontans during the early Cambrian. Here we describe Lyrarapax trilobus n. sp. from the same fossil Konservat-Lagerstätte. The new species differs from L. unguispinus in the morphology and distribution of endites on the frontal appendage and the strengthening structure of the body flaps. The two species resemble each other in body shape (pattern of flap size), neck segment number, cephalic plates, and most importantly a mouth characterized by concentric wrinkled furrows. The latter confirms that a soft mouth without sclerotized plates is a real feature of Lyrarapax and supports the idea that oral structures provide valid diagnostic characters within Radiodonta.

A new species of the artiopodan arthropod Acanthomeridion from the lower Cambrian Chengjiang Lagerstätte, China, and the phylogenetic significance of the genus

New material of the rare arthropod Acanthomeridion, including Acanthomeridion anacanthus sp. nov., is described from the lower Cambrian Chengjiang biota, Yunnan Province, China. The material includes a specimen with paired gut diverticulae along the length of the mid-gut that resemble structures in other artiopodan arthropods such as naraoiids. Previous phylogenetic analyses have indicated a petalopleuran/xandarellid affinity for Acanthomeridion, but our analysis resolves Acanthomeridion outside the main subclades of the Artiopoda (Aglaspidida + Trilobita, Nektaspida, Cheloniellida + Xenopoda, Conciliterga, Petalopleura (including Xandarellida)) as the most basal artiopodan. http://zoobank.org/urn:lsid:zoobank.org:pub:3563C327-EF9C-4A49-B200-417CE5D95D60

The enigmatic metazoan Yuyuanozoon magnificissimi from the early Cambrian Chengjiang Biota, Yunnan Province, South China

Abstract. Vetulicolians are a group of exclusively Cambrian animals characterized by an anterior section with lateral pouches and a posterior section that appears segmented. The precise phylogenetic affinity of vetulicolians is debated because there is a lack of consensus regarding the interpretation of their anatomical features. Their disparate morphology might even cause one to question whether this is a monophyletic taxon. In total, there are 15 species grouped into three families included in vetulicolians. Here we focus on new specimens of Yuyuanozoon magnificissimi Chen, Feng, and Zhu in Chen et al., 2003, a species that was first described from only a single specimen from the Chengjiang Biota (Cambrian Series 2, Stage 3, Eoredlichia-Wutingaspis trilobite Biozone), Yunnan Province, China. The species is notable in being exceptionally large (up to 20 cm long). Morphological observations on the new specimens clarify the nature of the wide circular opening at the presumed anterior end of the animal and the cowl-shaped lateral openings within this anterior section. Taphonomic observations identify wrinkles in the anterior section and twists in the posterior segmented section. In particular, the shape of the anterior opening of Yuyuanozoon magnificissimi suggests significant differences from other vetulicolians. Taxonomic reappraisal of Y. magnificissimi indicates that it belongs within the family Didazoonidae, as that is presently defined.

Telson morphology of Leanchoiliidae (Arthropoda: Megacheira) highlighted by a new Leanchoilia from the Cambrian Chengjiang biota

HE, YY., CONG, PY., LIU, Y., EDGECOMBE, GD., HOU, XG., May 2017. Telson morphology of Leanchoiliidae (Arthropoda: Megacheira) highlighted by a new Leanchoilia from the Cambrian Chengjiang biota. Alcheringa 41, 581–589. ISSN 0311-5518. Despite being a dominant group in both the Burgess Shale and the Chengjiang biota, diversity of the family Leanchoiliidae mostly consists of monotypic genera, with one genus, Leanchoilia, however, being represented by multiple species from several Cambrian Konservat-Lagerstätten. Here we distinguish a new species of this genus from hundreds of specimens formerly assigned to the Chengjiang species Leanchoilia illecebrosa, and establish its affinity within Leanchoilia by morphology of the telson (distally pointed and fringed with spines), a widely used diagnostic character at the generic level in Leanchoiliidae. The new species, Leanchoilia obesa sp. nov., is distinguished from other species of Leanchoilia by an oval outline of the dorsal exoskeleton and a telson with a long basal region and long spines. The new species is also distinguishable from other species of Leanchoilia by sharing some distinct characters of other leanchoiliid genera such as the wide body shape of Oestokerkus and Yawunik, and tiny serrations on the spinose projection of the great appendages of Yawunik. The mosaic combination of characters at the generic and specific levels prompted a re-evaluation of telson morphology as a diagnostic character in Leanchoiliidae. A new descriptive model of the leanchoiliid telson is based on the development of Leanchoilia obesa, inferred by comparing larval, juvenile and adult specimens. The result reveals that the leanchoiliid telson is a complex morphological unit and a source of diagnostic characters at both the generic and specific levels. Yu-Yang He [heyuyang850604@126.com], Pei-Yun Cong [cong@ynu.edu.cn], Yu Liu [zac.liu@126.com], Xian-Guang Hou* [xghou@ynu.edu.cn] Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, PR China; Pei-Yun Cong [p.cong@nhm.ac.uk], Gregory D. Edgecombe [g.edgecombe@nhm.ac.uk] Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.