"We may not know about all organisms present in the ancient world since not all organisms on Earth can be fossilized". The best statement is that Organisms that have soft bodies decay before they fossilize.
The animals represented via way of means of those newly found fossils, which include sponges, annelid worms, mollusks, and horseshoe crabs, lived at some stage in the Ordovician length among 480 million and 472 million years ago, making them the oldest ever found at some stage in this length.
For a soft-bodied animal to be fossilized, its frame should be blanketed from decomposition. The frame is typically uncovered to air and water with quite a little oxygen, so it decomposes rapidly. The animal is probable to be fossilized best if it's miles buried quickly after it dies (or whilst it's miles buried may be fossilized.
Read more about the decomposition:
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