HASnear corals, sponges. Clearly, current zoology research appreciates little-known animals. Or rather those of which many do not know that they belong to the animal kingdom. On May 28, the review Royal Society Open Science thus published a description of the sexual orgy in which corals indulged in a Japanese aquarium. A spectacle as exciting as it was impressive which we reported on. On June 5, it’s the turn of Nature to publish an astonishing article which brings a new, potentially major, piece to an old controversy relating to the first sponges, one of the most primitive animals we know.
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Because, let us remember here, sponges are animals. No brain, no muscles, no digestive system. Simply a body built around channels, which filters water, rejects waste, all attached to a rock. However, the nature of cells, reproduction, with the presence of spermatozoa, or even the mode of feeding indisputably place the approximately 15,000 listed species of the phylum Porifera – its scientific name – in the large family of critters.
If this question has been settled since the 1850s, another controversy fascinates the “spongists”: the origin of their favorite animal. Or, more precisely, how long has it existed and in what form? Modern genomics indeed makes it possible to go back in time. And the hands of this molecular clock point well beyond the Cambrian, a period of explosion of diversity that began 539 million years ago. Biomarkers found in rocks, supposed witnesses of porifera, confirm these data. Sponges appear at least 650 million years ago. There’s only one thing missing: fossils. Precambrian samples have been well advanced. In 2021, already in Nature, one article even turned the clock back to 890 million years ago. But the scientific community remains largely doubtful.
A morphological study
The last article is less greedy. The fossil that the international team (China, United Kingdom and United States), led by Shuhai Xiao, from the geosciences department of Virginia Tech, in the United States, is located in a range oscillating between 551 and 539 million years. Before the start of the Cambrian, therefore. To find it, Chinese scientists traveled through the Yangtze Valley in Sichuan. Local farmers use Shibantan limestone on the roofs of buildings. A fossil discovered on a tile of a pigsty allowed them to target a quarry. And that’s where they found their rare gem.
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