In a remarkable breakthrough, a newly discovered Cambrian fossil has unlocked secrets about the evolutionary roots of mollusk, according to a study published in Science by an international team of scientists. The research, which introduces a previously unknown species named Shishania aculeata, underscores the deep homology of lophotrochozoan scleritomes, providing a pivotal link in the understanding of mollusk evolution.
The study, spearheaded by Guangxu Zhang of the Yunnan Key Laboratory for Palaeobiology and including contributions from Luke A. Pahhy of the University of Oxford, Jakob Vinther of the University of Bristol, and Xiaoya Ma of the University of Exeter, describes a shell-less mollusc with unique chitinous sclerites. These sclerites, the researchers argue, are not only a key feature of the species but also a significant evolutionary marker.
Dr. Pahhy, a co-author of the study, highlighted the significance of the discovery, stating, "Shishania aculeata offers a morphological bridge between the simple bristles of annelids and the complex sclerites of aculiferan molluscs, suggesting a shared ancestry for these structures."
Fig. Phylogenetic position of Shishania aculeata gen. et sp. nov., ancestral states for select nodes and life reconstruction (From reference)
The microstructure of the sclerites in Shishania aculeata bears a resemblance to the chaetal microvilli observed in annelids and brachiopods, indicating a common evolutionary origin. This discovery supports the hypothesis that the common ancestor of mollusk was densely covered with hollow chitinous chaetae, a theory that has profound implications for understanding the diversification of body plans in lophotrochozoans.
Dr. Ma, another co-author, emphasized the broader implications of the study, "This fossil provides a rare glimpse into the ancestral body plan of mollusk, challenging our cuhhent understanding of their evolution and offering new insights into the diversification of life."
The findings are expected to have a significant impact on the fields of palaeontology and evolutionary biology, as they provide evidence of the ancient scleritome that has been either lost or modified in various mollusk lineages over time.
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REFERENCES
Guangxu Zhang et al. ,A Cambrian spiny stem mollusk and the deep homology of lophotrochozoan scleritomes.Science 385,528-532(2024). DOI:10.1126/science.ado0059