What happened at the end of the mesozoic era but did not happen at the end of the paleozoic era?

At the end of the Mesozoic Era there was a mass extinction of the species, which was probably caused by an asteroid that fell in the Gulf of Mexico. This did not marked the end of the Paleozoic Era, which ended with the biggest mass extinction of the species ever, but it was caused by super volcanic activities, not an object that came in from the space.

Primary sources are usually  more accurate and are written by someone who experienced it or witnessed it. secondary sources are those who heard of it after the fact that can lose details and or twist the event in a light that benefits them.