How many species belong to the class Mammalia?

The class Mammalia, commonly known as mammals, includes a diverse group of species characterized by features such as the presence of mammary glands, fur or hair, and three middle ear bones. As of the most recent classifications, the estimated number of recognized mammal species hovers around 5,400. This figure reflects ongoing taxonomic research and discoveries that continue to identify and describe new species, as well as refine classifications based on genetic and morphological data. The number is substantially higher than the other options provided, indicating a robust diversity within this class, which includes not only well-known groups like primates and marine mammals but also a variety of less familiar species. This understanding of mammalian diversity is crucial for studying ecological roles, evolutionary relationships, and conservation efforts.