Complex sentence: Opitsch had become more defensive about the fossil after in 1973 another exemplar had been announced, the Eichstätt specimen, which was much more complete and also transpired to have already been discovered in 1951, five years before the Maxberg.
Split into simpler sentences: Opitsch had become more defensive about the fossil after an announcement of another specimen in 1973. This was the Eichstätt specimen, which was much more complete and also transpired to have already been discovered in 1951, five years before the Maxberg.