I was watching this video from the Youtubers SciShow titled "7 Animals We Used to Think Were Extinct (But Aren't!)." Some of the extinct animals, were suspected to have gone extinct close to half a billion years ago, which leads me to believe that their fossils were obviously found in layers corresponding to those time periods and not in newer layers; however, since these animals are known to be still present today, I was wondering how it is possible that they do not have fossils in newer layers of the earth. Similarly, What caused the sudden stoppage of fossils?
I know very little about evolution, biology, and fossil records except from what is taught in high-school, and haven't taken a biology course in a few years, so if it is possible to get a simple answer that a biology ignorant person could understand I would greatly appreciate it! Thank you!