An armoured Cambrian lobopodian from China with... : Nature (original) (raw)

An armoured Cambrian lobopodian from China with arthropod-like appendages

Nature

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February 24, 2011

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| DOI: 10.1038/nature09704

Cambrian fossil Lagerstätten preserving soft-bodied organisms have contributed much towards our understanding of metazoan origins. Lobopodians are a particularly interesting group that diversified and flourished in the Cambrian seas. Resembling ‘worms with legs’, they have long attracted much attention in that they may have given rise to both Onychophora (velvet worms) and Tardigrada (water bears), as well as to arthropods in general. Here we describe Diania cactiformis gen. et sp. nov. as an ‘armoured’ lobopodian from the Chengjiang fossil Lagerstätte (Cambrian Stage 3), Yunnan, southwestern China. Although sharing features with other typical lobopodians, it is remarkable for possessing robust and probably sclerotized appendages, with what appear to be articulated elements. In terms of limb morphology it is therefore closer to the arthropod condition, to our knowledge, than any lobopodian recorded until now. Phylogenetic analysis recovers it in a derived position, close to Arthropoda; thus, it seems to belong to a grade of organization close to the point of becoming a true arthropod. Further, D. cactiformis could imply that arthropodization (sclerotization of the limbs) preceded arthrodization (sclerotization of the body). Comparing our fossils with other lobopodian appendage morphologies—see Kerygmachela, Jianshanopodia and _Megadictyon_—reinforces the hypothesis that the group as a whole is paraphyletic, with different taxa expressing different grades of arthropodization.

Lobopodia Snodgrass, 1938

Xenusia Dzik & Krumbiegel, 1989

Diania cactiformis gen. et sp. nov.

Etymology.

Dian represents a linguistic abbreviation in Chinese of the Yunnan province, where the Chengjiang fossil Lagerstätte is located; cactiformis refers to its overall cactus-like shape, which resulted in its nickname ‘walking cactus’.

Holotype.

ELI-WT006A,B (Fig. 1a–d), part and counterpart of the complete specimen, which was collected in 2006 from the Jianshan section, Haikou, Yunnan, southwestern China. ELI is an abbreviation of the Early Life Institute, Northwest University, Xi’an, China.

Open multimedia modal

Figure 1 | The early Cambrian lobopodianOpen multimedia modal

Diania cactiformis gen. et sp. nov. from the Chengjiang fossil Lagerstätte, Kunming, Yunnan, China. a–d, Holotype ELI-WD006A,B. a, Part of holotype photographed under ethanol, revealing almost all morphological features; note that the specimen is twisted towards the anterior end and the appendages are consequently slightly disordered, especially the fourth right appendage protruding under the trunk and appearing on the left side and the fifth right appendage protruding above the trunk and appearing again on the left side. b, Camera lucida drawing of a. c, Detail of the anterior part of a, which shows that the appendages are not preserved in the same layer; probably the specimens are to some extent three-dimensional. d, Counterpart of holotype. e, f, Specimen ELI-WT002A,B; although the specimens are incomplete, the appendages have clear annulations at the base and joint-like structures. aba, annulations of the base of appendages; an, annulations; bds, base of the dorsal spines; dls, disc-like structure; fls, fold-like structures; jls, joint-like structures; la, left appendage; mt, muscle tissue; pr, proboscis; ra, right appendage; pp, posterior protrusion; tis, tiny spine; tu, tubercle; wr, wrinkle. Scale bars, 10 mm.

Locality.

Yu’anshan (Heilinpu) Formation (Wutingaspis–Eoredlichia Zone).

Horizon.

Cambrian Stage 3.

Diagnosis.

Armoured lobopodian with ten pairs of appendages. Trunk region with nine segments, bearing rows of transverse annulations each with some tubercles. Each region possesses a pair of robust and sclerotized spiny appendages with primary articulation. Anterior is extended, probably forming a proboscis. Posterior region bears a protrusion.