AsianScientist (Sep. 30, 2019) – An international team of scientists has documented the death march of a segmented bilaterian animal unearthed from ~550-million-year-old rocks in China. Their findings are published in the journal Nature.
The origin of bilaterians with a segmented body plan is a monumental event in early animal evolution. Although scientists have estimated, on the basis of molecular clock analyses, that mobile and segmented bilaterians evolved in the Ediacaran Period (635-539 million years ago), no convincing fossil evidence had been found to substantiate these estimates.
In the present study, researchers at the Nanjing Institute of Geology and Palaeontology, China, in collaboration with Virginia Tech, US, have found direct fossil evidence of a segmented bilaterian fossil preserved in ancient rocks in China.
Discovered in the Yangtze Gorges area in China, the fossil is unusual in the sense that it was identified together with a trail it made. The researchers have named the fossil species Yilingia spiciformis, describing it as an elongate and segmented bilaterian with repetitive body units comprising three lobes each, and showing anteroposterior and dorsoventral differentiation.
Because one specimen was connected with the trail it produced immediately before death, the authors were able to infer that Y. spiciformis was a mobile animal capable of locomotion. However, the authors were unable to exactly determine its exact phylogenetic position within the bilaterian family tree. They surmise that Y. spiciformis could be related to arthropods—ancestors of modern day insects and crabs, or annelids—ancestors of modern day worms and leeches.
As one of the few Ediacaran animals demonstrably capable of producing long and continuous trails, Y. spiciformis sheds new light on the origin of segmentation and its possible relationship with animal motility. The emergence of motile animals had a profound environmental and ecological impact on Earth surface systems and ultimately led to the Cambrian substrate and agronomic revolutions, said the researchers.
The article can be found at: Chen et al. (2019) Death March of a Segmented and Trilobate Bilaterian Elucidates Early Animal Evolution.
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Source: Chinese Academy of Sciences; Photo: Nanjing Institute of Geology and Palaeontology.
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