Simplify the following text for a Grade 6 native English-speaking person.
Original: No further fossils had been recovered until January 1993 , when a trial dig on the site using an excavator rediscovered the fossil stratum , where the mass mortality of fishes was preserved in detail ( see LagerstÃ tte ) .
Simplified: More fossils were found in January 1993 using an excavator to dig down to the fossil layer . Many fish were preserved in detail .