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A 163-million-year-old fossil discovered in Inner Mongolia — dubbed Megacauda sungei — is the earliest known mammaliform capable of suckling, with preserved throat and hyoid bones revealing how modern mammal feeding evolved before living mammal lineages emerged.

What is a key fact in this story? (1)

**Zhe-Xi Luo** of the University of Chicago and colleagues identified the new genus *Megacauda sungei*, a semi-aquatic mammaliform dated to 163–168 million years ago and found by local farmers in the Daohugou area of Inner Mongolia, China.

What is a key fact in this story? (2)

**Megacauda** weighed roughly 1 kilogram, making it the largest known mammaliform from the Middle-Late Jurassic, when dinosaurs dominated terrestrial faunas.

Stunning early mammal fossil sheds light on the evolution of suckling — SkimNews

By New Scientist · Summarized & edited by Kapil Samant · 2026-10-07

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Zhe-Xi Luo of the University of Chicago and colleagues identified the new genus Megacauda sungei, a semi-aquatic mammaliform dated to 163–168 million years ago and found by local farmers in the Daohugou area of Inner Mongolia, China.
Megacauda weighed roughly 1 kilogram, making it the largest known mammaliform from the Middle-Late Jurassic, when dinosaurs dominated terrestrial faunas.
The fossil preserves 3D pelvis, hyoids, and the bones beneath the skull that form the roof of the mouth and throat — the first time scientists could reconstruct an entire mammaliform throat and confirm it could generate the suction vacuum needed for suckling milk.
Megacauda is a "chimera," Luo says: its broad back half resembles a platypus while its skull and teeth are analogous to a river otter's, reflecting its semi-aquatic lifestyle.
Limb fragments found in the creature's stomach area resembled salamander bones, suggesting salamanders sharing its habitat were part of its diet and possibly its last meal.
Oliver Griffith at Macquarie University said the fossil demonstrates that key mammalian traits like suckling — needed for drinking milk from mothers — predate the origin of today's mammal groups, and that aquatic lifestyles evolved independently in this sister lineage as they later did in the platypus.

Why it matters: With Megacauda's throat anatomy preserved in 3D, paleontologists can finally pin the origins of mammalian suckling to 163–168 million years ago — well before the common ancestor of monotremes, marsupials, and placentals — reshaping the timeline for when milk-feeding and the suction-based swallowing unique to mammals first evolved.