Generation IV introduced 107 new Pokémon species in its main games.
Generation IV began with Pokémon Diamond and Pearl for the Nintendo DS and was later expanded by Pokémon Platinum. Its new species belong to the Sinnoh region, whose landscape, mythology, and Pokédex form the foundation of that generation’s story.
The additions include starters such as Turtwig, Chimchar, and Piplup; Legendary Pokémon such as Dialga, Palkia, and Giratina; and several new evolutions for Pokémon from earlier generations. Those cross-generation evolutions helped make the Sinnoh Pokédex feel connected to the franchise’s history.
The figure 107 refers to species newly introduced in Generation IV, not the cumulative Pokédex total. Adding them to the 386 species available after Generation III produced a total of 493. Later games and expansions added many more Pokémon, so the generation-specific number should not be confused with the overall franchise count.