A Cambrian unarmoured lobopodian, \u2020Lenisambulatrix humboldti gen. et sp. nov., compared with new material of \u2020Diania cactiformis

Qiang Ou,Georg Mayer

doi:10.1038/s41598-018-31499-y

Qiang Ou, Georg Mayer

Open Access

https://doi.org/10.1038/s41598-018-31499-y

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Abstract

Cambrian marine lobopodians are generally considered as predecessors of modern panarthropods (onychophorans, tardigrades, and arthropods). Hence, further study of their morphological diversity and early radiation may enhance our understanding of the ground pattern and evolutionary history of panarthropods. Here, we report a rare lobopodian species, †Lenisambulatrix humboldti gen. et sp. nov. (“Humboldt lobopodian”), from the early Cambrian Chengjiang Lagerstätte and describe new morphological features of †Diania cactiformis, a coeval armoured lobopodian nicknamed “walking cactus”. Both lobopodian species were similar in possessing rather thick, elongate lobopods without terminal claws. However, in contrast to †Diania cactiformis, the body of which was heavily armored with spines, the trunk and limbs of the Humboldt lobopodian were entirely unarmored. Our study augments the morphological diversity of Cambrian lobopodians and presents two evolutionary extremes of cuticular ornamentation: one represented by the Humboldt lobopodian, which was most likely entirely “naked”, the other epitomized by †D. cactiformis, which was highly “armoured”.

Highlights

Lobopodians were marine, caterpillar-like Palaeozoic animals characterized by non-segmented limbs called lobopods or lobopodia
We describe a new taxon, †Lenisambulatrix humboldti gen. et sp. nov., which arguably shows the lowest degree of modification of appendages and the absence of ornamentation on trunk and appendages
The considerable expansion some distance away from the distal end of the body terminus is reminiscent of Cambrian lobopodians with an expanded head region, such as †Cardiodictyon catenulum and †Hallucigenia fortis

Summary

Introduction

Lobopodians were marine, caterpillar-like Palaeozoic animals characterized by non-segmented limbs called lobopods or lobopodia (singular: lobopodium; from Greek λοβός [lobos], rounded projection or protuberance; and ποδός [podos], foot). Recent phylogenetic analyses resolved the clustering of (i) hallucigeniids (including representatives of †Hallucigenia, †Cardiodictyon, †Carbotubulus, and probably †Microdictyon) characterized by one to three pairs of modified (slender, tentacle-like) anterior appendages and a well-differentiated head[5]; (ii) luolishaniids (including representatives of †Luolishania, †Collinsium, †Acinocricus, “Collins’ monster”, and probably †Facivermis) distinguished by pairs of modified (elongated, spinous, suspension-feeding) anteriormost and even specialized posteriormost appendages (e.g., †Ovatiovermis cribratus)[3,5]; and (iii) the “large lobopodians” (representatives of †Jianshanopodia, †Megadictyon, †Hadranax, †Kerygmachela, †Pambdelurion, and †Siberion), which comprise a paraphyletic assemblage closely related to arthropods[3,5] These three groups show varying degrees of appendage specialization and tagmosis (body tagmatization). We describe a new taxon, †Lenisambulatrix humboldti gen. et sp. nov., which arguably shows the lowest degree of modification of appendages and the absence of ornamentation on trunk and appendages, www.nature.com/scientificreports/

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