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The Jurassic mammaliaform Microdocodon gracilis preserves a hyoid apparatus—small bones and related structures in the throat—that supports the inference that it could suckle. The fossil offers evidence about an early mammal relative’s feeding capability, not a direct record of an animal nursing.
What does the Microdocodon fossil tell us about nursing?
A 2019 Nature feature describes Microdocodon gracilis as a docodont, an extinct close relative within the mammaliaform lineage, that lived about 165 million years ago. Its preserved hyoid apparatus is associated with the tongue and throat, structures involved in feeding. The feature interprets this anatomy as evidence that the animal was capable of suckling.
The distinction matters: the bones are fossil evidence; suckling is a behavior inferred from them. The specimen does not preserve a feeding event, so it cannot directly show an infant nursing.
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How did mammals evolve suckling?
The 2023 review of mammalian feeding evolution treats the origins of lactation and suckling as related but distinct questions. Suckling is the infant’s feeding behavior; lactation is milk production by the parent. Their evolutionary histories need not be described as one event.
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The review says the origins of lactation and suckling behavior probably predated or occurred near the origin of mammals, while maternal and infant functions diversified later, after mammalian features were established. It also discusses fossil evidence for lactation among mammaliaforms. That broader picture provides context for Microdocodon, but this specimen alone does not establish every step in the evolution of milk production or infant feeding.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Is Microdocodon the first animal known to suckle?
The Nature feature calls Microdocodon gracilis “the earliest animal known to have been able to suckle like a modern mammal.” That is the feature’s characterization of the evidence, not a claim that this fossil definitively marks the first origin of suckling. Fossil discoveries can extend the known record, and behavior is inferred from preserved anatomy rather than observed directly.
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