Answer: Platypus.
Some extra relevant information:
Among the given options, mammals are the group that does not lay eggs. Unlike reptiles, birds, amphibians, and most fish, mammals give birth to live young. This characteristic sets mammals apart from other animal groups and is one of the defining features of the class Mammalia.
Mammals have evolved unique reproductive strategies that involve internal fertilization, gestation, and nurturing the developing offspring within the mother’s body. This process allows for a more advanced level of parental care compared to egg-laying animals. It enables mammals to provide their young with all the necessary nutrients, protection, and support until they are ready to survive independently.
From tiny mice to enormous whales, mammals display a wide range of reproductive adaptations. They have developed various methods to sustain pregnancy, such as placentas, pouches, or simply nurturing the young with milk produced by specialized mammary glands.
While mammals do not lay eggs, there are some exceptions among them. The platypus and echidna, both found in Australia, are monotremes, a primitive group of mammals that lay eggs. These fascinating creatures combine reptilian-like egg-laying with mammalian characteristics, such as milk production, making them unique within the animal kingdom.
In conclusion, among the options provided, mammals are the group that does not lay eggs. Their reproductive strategy involves giving birth to live young and providing them with nourishment and care until they are ready to survive independently.