In comparison with the millions that must have actually lived over that period.
Fact is, we're just not very good at getting ourselves fossilised and into the record.
For all the reasons that Buildreps gives. We haven't been around for long enough, were too small, we tend to not die in swamps.
How many of all species were never fossilised? Palaeontologists estimate just a tiny fraction lucky enough to be fossilised and even more lucky to be discovered. Most lost forever.
So if you're planning on getting yourself fossilised, be around for a good few millions of years, be big, be numerous and hang around a swamp.
You could say there are more holes in the fossil record than fossil record.
Edited 5 time(s). Last edit at 31-Dec-16 15:25 by Jon Ellison.