Sponges have lived on the earth for at least 540 million years, and are one of the earliest animal classes that appeared in the Phanerozoic. But their early evolutionary history is still not fully understood so far, the main reason is that they are not easily preserved completely as fossils. Early studies on the classification of sponge evolution rely on molecular biological evidence of modern biological species, and recently, through the study of early sponge fossil bone structure, surprising conclusions have been obtained.
Today's sponges can be divided into two categories according to the mineralization of bone needles: silicea sponges based on opal bone needles and calcareous sponges based on calcite bones (Calcarea). The methods and styles of the cavernous body for making these mineralized bone needles are complex and varied. Generally speaking, these two types of sponges use different chemical mechanisms and cells to construct the shape and arrangement of bone needles. Therefore, most scholars believe that these two types of sponge branches are very early and are the products of independent evolution based on the observation of current biological species.
A research team composed of Dr. J. Botting, Dr. L. Muir, Researcher Xiao Shuhai, Master Student Li Xiangfeng, and Researcher Lin Ribai, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, recently published in the International Journal of Paleontology and Stratigraphy The latest results published show a completely different result from previous understanding. Through scanning electron microscope observation and composition analysis, it was found that in the early Cambrian (up to 520 million years ago) Hetang sponge biota, the bone needle of the difficult sponge Lenica had both a siliceous layer and a carbonate layer. Combining the analysis results of multiple samples, scholars speculate that the bone needle of this sponge has a layered structure, the silicon core is surrounded by a thick layer of calcareous layer, and the organic membrane is wrapped in the outermost layer.
This result shows that it is difficult to classify early sponge bone needles in the category of modern sponges. Part of the reason may be that these sponges are not belonged to the existing sponges, but are side branches that had been extinct before the appearance of the existing sponges.
Information about the paper: Botting, JP, Muir, LA, Xiao, S., Li, X.-F. & Lin, J.-P. 2012. Evidence for spicule homology in calcareous and siliceous sponges: biminerallic spicules in Lenica sp. (Porifera;? Protomonaxonida) of early Cambrian age (535-520 Ma) from South China. Lethaia 45, 463-475.
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