【古生物学】カンブリア紀に「引きこもり」生活をしていた蠕虫似の動物の化石

A new species of lobopodian - a worm-like, soft-legged animal from the Cambrian period (541 to 485 million years ago) - is described in a study in Scientific Reports. Qiang Ou and Georg Mayer compared the new species, named Lenisambulatrix humboldti, to another previously described lobopodian, Diania cactiformis, about which they offer new details.

The researchers show that both lobopodians had similarly shaped, segmented bodies and possessed thick, long legs (lobopods) that measured between 11.6 to 18 millimetres. Unlike other lobopodians, neither species appears to have had any claws. However, in contrast to D. cactiformis, which has been nicknamed ‘walking cactus’ because its body was heavily armoured with spines, L. humboldti appears to have been entirely without armour.

The authors describe the new species as having a tubular, segmented trunk - similar to a worm - with each segment bearing a pair of limbs. Only one end of the animal’s body is preserved and it bears no distinguishing features, such as eyes, a mouth or tentacles that would allow it to be recognized as a head. By contrast, the presumed head end of D. cactiformis shows a distinctive helmet-like structure.

The morphology of both species suggest some insights into how they may have lived; as both were sea-dwellers, their clawless legs may have been adapted for walking or crawling on the soft seafloor. Whereas D. cactiformis’ heavy armour may have protected it from predators, the soft body of L. humboldti may indicate that individuals of this species lived a reclusive life, hiding in crevices or among clusters of sponges to avoid predation.