When mass extinctions occur, as they have five times previously in Earth’s history, every member of a given species expires. Not just the old, the infirm, those who have a certain vulnerability. All members of the species die, even the babies.
After spotting dozens of limestone skulls of extinct creatures on Lake Michigan’s Left Coast, I started noticing tiny chert rocks in the same shapes. Chert is harder than limestone; smaller skulls fossilized in chert would survive longer than tiny limestone skulls.
I know these are vague. I typically look for samples with visible fossilized teeth, which give credence to my claim that a hunk of rock is in fact a Paleozoic skull. Skulls of babies baring teeth are a little hard to find, though potential specimens number in the millions. I will keep looking.