Gigantism

Gigantism is exceptionally large body size in an organism relative to close relatives or ancestral forms. It can arise through different evolutionary, developmental, or environmental processes.

Insulin-like growth factor 1: A hormone and growth factor that promotes cell growth and skeletal development in vertebrates. Changes in this pathway can alter growth, especially in mammals.
Cope's rule: The proposed tendency for animal lineages to evolve larger body sizes over geological time. It offers a broad evolutionary pattern relevant to, but not universal in, gigantism.
Sauropoda: A group of long-necked, long-tailed herbivorous dinosaurs that included the largest land animals known. Sauropods represent extreme terrestrial gigantism in the fossil record.
Pituitary gigantism: Excessive linear growth in childhood caused most often by excess growth hormone from a pituitary tumor. It is a specific medical condition sharing the name but not the evolutionary meaning.
Growth hormone: A pituitary hormone that stimulates growth and influences metabolism. Excess secretion before growth plates close can cause pituitary gigantism.
Island rule: The tendency for large mainland animals to become smaller and small animals larger on islands. It places island gigantism within a wider pattern of size shifts.
Blue whale: A baleen whale and the largest animal known to have lived. Its exceptional size is an extreme case of marine gigantism.
Acromegaly: A disorder caused by excess growth hormone after the growth plates have closed, enlarging hands, feet, and facial features. It distinguishes adult hormone-related tissue enlargement from childhood gigantism.
Allometry: The study of how body parts and biological rates scale with organism size. It describes how body proportions and physiological demands change as gigantism evolves.
Foster's rule: The hypothesis that isolated island species evolve body sizes different from mainland relatives, often toward an intermediate size. It is an early formulation of the evolutionary pattern behind island size changes.

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