Three fossils from the Early Cambrian which have long posed a puzzle to scientists belong to the same primeval creature. This has been shown in studies of new finds from the so-called Chengjiang deposits dating back to more than 500 million years ago. Paleontologist Dr. Qiang Ou, a guest researcher working together with Prof. Dr. Georg Mayer at the University of Kassel, played a significant role in the new discovery. These findings provide new insights regarding the evolution of the diversity of species during the so-called Cambrian explosion.
Based on the findings of Ou, Mayer, and additional co-authors of the study, the primeval creature †Xianguangia sinica, which lived approximately 520 million years ago, was an ancestral cnidarian, contrary to what was previously believed. The cnidarians today include jellyfish, corals, and sea anemones.
The animal measured approximately five centimetres in height and resembled a polyp, but possessed an additional body cavity that apparently served as a hydrostatic skeleton within an anchoring device at the base of the body. Feather-like tentacles with numerous cilia were characteristic for the species and served for capturing food particles from the water column.
“The ‘feather polyp’,” as the scientists informally named †X. sinica, “was a so-called suspension feeder,” says Mayer. This means that it filtered organic particles from the surrounding water through the action of cilia that transported food material towards the mouth. This finding refutes previous hypothesis that †X. sinica was a predator which, like most living cnidarians, caught macroscopic planktonic organisms using simple, unbranched tentacles laden with venomous cnidocytes.
The scientists have now been able to clarify the contradictory classification of the fossils †Chengjiangopenna wangii (a purported Cambrian “sea pen”) and †Galeaplumosus abilus (the “oldest hemichordate”). It now has become evident that these fossils are simply body fragments of †X. sinica. Previously, they had been incorrectly identified and described as separate species.
The detailed reconstruction of the body structure of †X. sinica was made possible by examining 85 new and exceptionally preserved specimens from the Chengjiang deposit in China. Ou, Mayer, and their colleagues examined these specimens using scanning electron microscopy (SEM) as well as energy-dispersive X-ray spectroscopy (EDX). In addition, the researchers conducted phylogenetic analyses in order to clarify the position of the fossil species in the animal tree of life. The results indicate that the diversity of cnidarian morphology and feeding behaviour was higher in the Cambrian than previously thought.
Major parts of this study were carried out at the University of Kassel where Dr. Qiang Ou (40) is conducting research as an Alexander von Humboldt Fellow in the Zoology department.
In the last decades, numerous previously unknown fossils have been discovered in the Chengjiang deposits, opening up new dimensions in our understanding of biodiversity in the Cambrian period. Many of these fossils, however, have not yet been completely and unequivocally analysed. The term "Cambrian explosion" refers to a massive emergence of new species during the Cambrian period approximately 530 million years ago.
The new results concerning the species †Xianguangia sinica have been published in the prestigious journal "Proceedings of the National Academy of Sciences of the United States of America": http://www.pnas.org/content/early/2017/07/26/1701650114.abstract
Prof. Dr. Georg Mayer
University of Kassel
Department of Zoology
Phone: +49 (0)561 804-4805
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