A 165-million-year-old swimming mammal relative already had a throat built for suckling
Researchers describing Megacauda sungei in Nature say the half-metre Jurassic swimmer had a throat built for suckling 165 million years ago. That puts the anatomy for milk-feeding earlier than the last common ancestor of all living mammals.
The Scientist · Science desk
What happened
- Preserved throat bones let the team reconstruct the entire throat anatomy of a mammaliform for the first time, according to New Scientist.
- Computed tomography reconstructions suggest the animal paddled with its front legs, moved its flattened tail in waves and steered with its hind legs.
- Tiny limb fragments resembling salamander bones lie in the fossil's stomach area and may be the remains of its last meal.
- The fossil is dated to between 163 million and 168 million years ago and was found by local farmers in the Daohugou area of Inner Mongolia.
Why it matters
- What it limits constraint The bones show that Megacauda could suckle. Whether its young actually drank milk is a separate question that one skeleton cannot answer.
- What doesn't add up contradiction Bonn's release puts the animal at about 2 kg and New Scientist at about 1 kg, so its title as the largest Jurassic mammaliform rests on mass estimates that differ twofold.
- What's now possible capability With one mammaliform throat now reconstructed in full, other Jurassic fossils that preserve hyoid bones have a reference to be compared against.
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Crocodiles show the alternative. They lack a soft palate and have only a simple hyoid apparatus, so they raise their heads and jerk unchewed prey down their throats [14]. "This is achieved with the aid of gravity," said Thomas Martin, a palaeontologist at the University of Bonn [16]. Mammals have a more complex hyoid structure in the pharynx and can swallow against gravity [6]. The soft palate separates the mouth from the pharynx so an animal can swallow and breathe at once, and the Bonn team calls it an important requirement for suckling [3]. Zhe-Xi Luo of the University of Chicago told New Scientist that a mammal's throat can form "a suction vacuum for milk and squeeze the chewed food balls and liquid down their throats" [21].
For Megacauda, the case rests on bone. New Scientist reports that the hyoids are preserved in three dimensions, as are the structures beneath the skull that form the roof of the mouth and the throat passage [19]. Every feature that enables suction and swallowing is present, according to the same account [22]. "We used to know very little about the evolutionary pattern of pharyngeal and hyoid structure. Now we know their evolutionary origins went back to before the rise of the modern mammals," Luo said [15].
Oliver Griffith at Macquarie University in Sydney described the finding in terms of traits. "It tells us that some key mammalian traits like sucking, which is required for behaviours like drinking milk from mothers, predate the origin of mammals today," he said [17]. Martin went further. "It was this adaptation that made brain development, eventually leading to humans, possible," he said [26]. In my view that second sentence is an argument about the lineage's later history. A single Jurassic skeleton can date the anatomy, but it cannot test that argument.
The thing this doesn't tell you is whether Megacauda sits on the line that led to living mammals. The Bonn release calls it a "furry ancestor of today's mammals" [10]. New Scientist places it before the last common ancestor of monotremes, marsupials and placentals [11], and Griffith called it a "sister lineage to today's mammals" [18]. I think Griffith's wording is the more precise of the two. Megacauda is a docodont, a member of an extinct group of early mammaliforms that lived mostly in the Jurassic [9].
The rest of the animal fits a life in water. "It is a chimera," Luo said. "The back half of Megacauda is more similar to the platypus, of all mammals. But the skull and teeth are analogous to river otters." [24] Its tooth cusps curve backward, which the Bonn team says helped it catch slippery prey, and its canines have three roots [8]. Martin called it "the earliest evidence of an aquatic lifestyle in mammals" [2].
What to watch
- The Nature paper's own body-mass figure, to settle whether Megacauda weighed about 1 kg or about 2 kg.
- Whether other docodont or mammaliform fossils with 3D-preserved hyoids show the same throat structure, or whether Megacauda remains the only example.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence74
- Adoption
- Not scored
- Hype gap+22
- Incentives
- Not scored
- Confidence70
Perspective Coverage
5 publishers- Builder
- Builder 74%
- Operator
- Operator 17%
- Investor
- Investor 9%
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Three-dimensional reconstructions from computed tomography images suggest the animal paddled with its front legs, moved its tail in a wavelike motion and used its hind legs to steer.
- [2]
"It is the earliest evidence of an aquatic lifestyle in mammals,"
- [3]
The soft palate separates the oral cavity from the pharynx while enabling swallowing and breathing; it is an important requirement for suckling, which provides a survival advantage.
- [4]
Martin says Megacauda sungei is the largest of the mammaliforms from the Jurassic; the animal weighed around two kilograms.
- [5]
The findings by researchers from the universities of Shenyang, Chicago and Bonn are published in the journal Nature.
- [6]
Mammals, with their complex hyoid structure in the pharynx, are able to swallow against gravity.
- [7]
With an estimated weight of 1 kilogram, the creature is the largest known mammaliform from the Middle-Late Jurassic.
- [8]
The cusps of its teeth curved backward to enable it to catch slippery prey; its specialized canines have three roots.
- [9]
The fossil, found in Xiayingzi, Inner Mongolia, is a docodont, a member of an extinct group of early mammaliforms that primarily lived in Jurassic times.
- [10]
The Bonn account describes Megacauda as the "furry ancestor of today's mammals".
- [11]
Megacauda is a mammaliform that lived before the last common ancestor of the living mammalian groups (monotremes, marsupials and placentals) and would have been able to chew and suck.
- [12]
The fossil is dated to between 163 million and 168 million years ago and was found by local farmers in the Daohugou area of Inner Mongolia, China.
- [13]
Megacauda sungei measures half a metre (1.6 feet) from nose to tail tip and hunted its prey in water 165 million years ago.
- [14]
Many animal species lack a soft palate and have only a simple hyoid bone apparatus without a swallowing mechanism; crocodiles raise their heads and use jerky movements to make unchewed prey slide down their throats.
- [15]
"We used to know very little about the evolutionary pattern of pharyngeal and hyoid structure. Now we know their evolutionary origins went back to before the rise of the modern mammals,"
- [16]
"This is achieved with the aid of gravity,"
- [17]
"It tells us that some key mammalian traits like sucking, which is required for behaviours like drinking milk from mothers, predate the origin of mammals today."
- [18]
"It also is cool to see that this sister lineage to today's mammals had evolved an aquatic lifestyle, which is something we have seen multiple times across the mammalian family tree, including in the platypus,"
- [19]
The pelvis and the hyoids (throat bones) are preserved in 3D, and the bone structures under the skull that form the roof of the mouth and throat passage are visible.
- [20]
For the first time in any mammaliform, scientists were able to reconstruct the animal's entire throat anatomy.
- [21]
Mammals' throats can form "a suction vacuum for milk and squeeze the chewed food balls and liquid down their throats"
- [22]
All the features that enable suction and swallowing are present in Megacauda.
- [23]
Tiny limb fragments resembling salamander bones were found in the fossil's stomach area and may have been the creature's last meal.
- [24]
"It is a chimera. The back half of Megacauda is more similar to the platypus, of all mammals. But the skull and teeth are analogous to river otters."
- [25]
The Bonn account's weight estimate (about 2 kg) is twice New Scientist's (about 1 kg).
- [26]
"It was this adaptation that made brain development, eventually leading to humans, possible,"
Sources
5 independent publishers whose own reporting we read for this story.
- discovermagazine.comNewly Identified 165-Million-Year-Old Otter-Like Mammal Was a Top Predator in Jurassic Waterways
1 article · October 7, 2026
- livescience.com'It looks like a chimera' — 168 million years ago, a strange platypus-like mammal relative lived in China alongside dinosaurs
1 article · October 7, 2026
- nature.comA Jurassic mammaliaform swimmer and transformation of the mammalian pharynx
1 article · October 6, 2026
- newscientist.comStunning early mammal fossil sheds light on the evolution of suckling
1 article · October 7, 2026
- phys.org'Top predator' from the Jurassic measures just half a meter
1 article · October 7, 2026
Topics and entities
Entities
- Paleontological Museum of Liaoning
- Megacauda sungei
- University of Chicago
- Nature
- University of Bonn