2023-10-11 11:29:36
SEM images of the microfossil NIGP179459 – ZHANG HUAQIAO
MADRID, 11 Oct. (EUROPA PRESS) –
Microfossils 535 million years old found in china They preserve the musculature of a group of animals that includes roundworms, mane worms, mud dragons, and other creatures.
The discovery, published in Proceedings of the Royal Society B: Biological Sciences, adds valuable information about early Cambrian cycloneurals, which are closely related to arthropods, the most successful animals on Earth.
The superphylum Ecdysozoa represents the most diverse animals with bilateral symmetry. Contains Scalidophora (Kinorhyncha, Loricifera, Priapulida), Nematoida (Nematoda, Nematomorpha) and Panarthropoda (Tardigrada, Onychophora, Arthropoda). Scalidophora and Nematoida constitute the Cycloneuralia, whose monophyly is the subject of debate.
Unambiguous fossils of ecdysozoan bodies first appeared in the early Fortunian era (535 million years ago) and are represented by the total group ecdysozoan taxon Saccorhytus and several cycloneural species of the crown group. However, the preservation of Fortunian ecdysozoans is limited to the cuticular integuments, with no labile internal tissues preserved (for example, muscles or nervous tissues), which hinders a greater understanding of its functional morphology and evolutionary significance.
In this study, the researchers –led by Professor Zhang Huaqiao of the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences (NIGPAS)- described three millimeter-sized phosphate specimens from the early Fortunian Kuanchuanpu Formation (535 million years old) of China. Among them, one specimen (NIGP179459) is better preserved and consists of five successively larger rings that are interconnected with 19 radial and 36 longitudinal structures. The rings were compressed to some extent, implying that they were flexible when alive.
The first ring is separated from the four remaining larger rings by a gap and is located almost coplanarly in the center of the second ring, or slightly apical. Radial structures connect the first ring to the third ring, while longitudinal structures extend from the third ring to beyond the fifth ring. Some longitudinal structures take on a more fibrous textural appearance towards the abapical end. In the reconstruction, the second to fifth rings are stacked coaxially and constitute an apically truncated conewith internal longitudinal structures arranged hexaradially.
Based on their arrangement patterns, fibrous texture and inferred flexibility, the rings, as well as the radial and longitudinal structures, They were interpreted as fossilized muscles. The preserved musculature consists of four groups of muscles, that is, one internal circular, four external circulars, 19 radial and 36 longitudinal.
This complex topology differs from that of the musculature of the body walls of basal animals such as cnidarians or ctenophores and, on the other hand, probably represents musculature of bilateral animals.
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