As a reminder, sponges are animals not plants…no brain, no digestive system, no muscles, a body made up of channels that filter water and reject waste, all while hanging on a rock. It is equipped with reproduction and spermatozoa, in short everything that is necessary. Especially unlike plants, these cells do not have the chloroplast needed for photosynthesis. The question arose of the origin of sponges or rather since when have they existed in this form. The genetic approach teaches us that sponges were born well before this period of explosion of diversity; approximately 500 million years ago.
Recent work dates them to 890 million years old based on fossils. It must be said that having no bone structure, fossils are not legion. This international team (China, United Kingdom and USA) discovered a fossil with a foot and a conical shape typical of sponges, attesting to an animal at the bottom of a lake and incapable of moving. Yet this is debated by other experts because they do not have spicules – these calcareous or silica secretions observed in modern sponges. The answer awaits new fossils, as is often the case in science, discoveries come when you are ready to discover them.
https://www.nature.com/articles/s41586-024-07520-y.epdf
Photo : nature.com
