Complex sentence: Proto-Mayan is the hypothetical common ancestor of the 30 living Mayan languages, and the direct ancestor of the dead Classic Mayan language documented in the Maya Hieroglyhical inscriptions.
Split into simpler sentences: Proto-Mayan is the hypothetical common ancestor of the 30 living Mayan languages. And the direct ancestor of the dead Classic Mayan language documented in the Maya Hieroglyhical inscriptions.