Iguanas do not have mammary glands. The presence of mammary glands is the biological trait that defines animals belonging to the class Mammalia. Iguanas are classified as reptiles and lack the specialized anatomical structures required for producing milk to nourish their young. Their reproductive strategy and the way their hatchlings survive are fundamentally different from those of mammals.
The Defining Role of Mammary Glands
Mammary glands are specialized exocrine glands that function exclusively to produce milk, a process known as lactation. The class name, Mammalia, is derived from these organs, making their presence the defining trait for classification. These glands are composed of glandular tissue, including alveoli lined with milk-secreting cells, and a ductal system that transports the milk to the nipple or teat.
The milk produced is a complex emulsion providing a balanced source of fats, proteins, sugars, vitamins, and antibodies to the newborn. This nourishment and immunological support allows mammalian young to be born relatively underdeveloped, relying entirely on the mother for initial survival. Lactation provided a significant advantage, ensuring growth and protection for offspring in their earliest stage of life.
Iguana Reproduction and Classification
Iguanas belong to the class Reptilia, and their biology follows the reproductive pattern typical of this group. As reptiles, iguanas do not possess the necessary anatomy for milk production, including specialized secretory tissue or the hormonal pathways that regulate lactation. Instead of bearing live young, iguanas are oviparous, meaning they reproduce by laying eggs.
The female iguana, such as the green iguana, digs a nest, often a deep burrow up to a meter or more, where she deposits a clutch of eggs. The number of eggs laid can range widely, from 10 to over 60 eggs in a single nesting event. Once the eggs are laid and buried, the female typically leaves the nest, providing no further parental care or sustenance to her offspring.
Post-Hatching Survival
The survival of iguana hatchlings is dependent on the resources provisioned within the egg and their own capabilities. The young lizard inside the egg absorbs nourishment from a large yolk sac, which often provides sustenance for the first week or two after hatching. When they emerge from the nest after an incubation period of 90 to 120 days, the hatchlings are considered precocial. This means they are relatively mature, mobile, and capable of independent action immediately.
These young iguanas do not rely on parental feeding and must seek out their own food sources immediately. Juvenile iguanas are omnivorous, consuming small invertebrates like insects and spiders, in addition to soft vegetation and fallen fruits. To establish the necessary microflora for their herbivorous adult diet, hatchlings often consume the feces of adult iguanas, acquiring the specialized gut bacteria needed to digest plant cellulose.