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| Massetognathus pascuali |
And then there is this charming little Massetognathus pascuali at the Natural History Museum Abu Dhabi, displayed vertically with his head raised and his forelimbs tucked neatly before him, as though he has just spotted an old friend approaching.
“Oh, hey guys! You made it.”
His actual sex is unknown, of course, but he has such a cheerful, expectant air that I immediately began thinking of him as a little fellow waiting to greet visitors.
His upright position is a museum display choice rather than a reconstruction of his normal posture in life.
Massetognathus travelled on all four limbs, but the arrangement gives us a wonderfully clear view of his compact skeleton—and an unexpectedly endearing introduction to one of the most important chapters in mammalian evolution.
Massetognathus pascuali lived in what is now northwestern Argentina during the Triassic Period, roughly 235 million years ago. At that time, the continents were joined into the supercontinent Pangaea, dinosaurs were only beginning their long evolutionary rise, and true mammals had not yet appeared.
Massetognathus was not a dinosaur. It was a cynodont: a member of the great synapsid lineage that also contains mammals and their extinct relatives. More specifically, it belonged to a group of plant-eating cynodonts called traversodontids.
This does not mean that Massetognathus was our direct ancestor. Evolution is rarely a tidy ladder leading solemnly toward us. It is an exuberantly branching family tree filled with cousins, experiments and entire lineages that flourished before disappearing. Massetognathus occupied one of those neighbouring branches on the mammalian side of the ancient amniote family tree.
Still, its anatomy helps us understand the wider evolutionary world in which recognizably mammalian features were developing.
The name Massetognathus is particularly appropriate. It is derived from words referring to a “chewing-muscle jaw,” and chewing was very much this animal’s specialty.
Unlike reptiles that simply seized food and swallowed it in large pieces, traversodontid cynodonts possessed differentiated teeth that could process vegetation inside the mouth.
At the front were incisors for nipping. Farther back were enlarged, broad postcanine teeth with complex crowns that met one another to crush and shear food.
These expanded teeth are often described as gomphodont—essentially “molar-like”—although they were not identical to the molars of modern mammals.
This was serious dental equipment.
Massetognathus probably fed largely on the leaves, stems and other available plant material of Triassic Gondwana. Its broad skull, powerful jaw muscles and specialized teeth suggest a generalized herbivorous diet.
Like a determined little prehistoric food processor, it could bite vegetation into smaller, more manageable pieces before swallowing it.
Studies of traversodontid skulls and limbs estimate that the largest adults of M. pascuali may have weighed somewhere between about 17 and 40 kilograms, although younger individuals were considerably smaller. The broad range reflects both growth and the difficulty of estimating body mass in animals with no exact living equivalent.
This was not, then, a mouse-sized creature scurrying unnoticed beneath dinosaur feet. A large adult may have been closer in mass to a medium-sized dog, though built very differently: low-bodied, sturdy and equipped with a disproportionately robust head.
Dog-sized (think border collie, beagle or small Labrador) but not dog-like. Its proportions were very different.
It had a long, low body, relatively short limbs and a large, sturdy head—so imagine something between a stocky dog and an oversized badger, equipped with broad teeth for grinding Triassic vegetation.
Its limbs also tell an evolutionary story.
Research suggests that the forelimbs retained a posture intermediate between sprawling and fully upright beneath the body, while the hind limbs were held more directly underneath it. Massetognathus occupied a fascinating anatomical middle ground—not half reptile and half mammal, which would be misleading, but an animal with its own successful combination of inherited and newly evolving characteristics.
The preserved skeletons of Massetognathus pascuali come primarily from the Chañares Formation of Argentina.
These rocks have yielded an extraordinary community of Triassic vertebrates, including dicynodonts, predatory cynodonts and early archosaur relatives close to the ancestry of dinosaurs.
Many Chañares animals were preserved within volcanogenic concretions. Volcanic activity produced enormous quantities of ash, and water moving across the landscape may have carried ash and sediment into low-lying areas. Animals buried in this material sometimes became enclosed within mineral-rich nodules, protecting their bones for more than 230 million years.
Massetognathus is especially valuable because numerous individuals representing different stages of growth have been discovered. These fossils allow researchers to investigate how its skull changed as the animal matured.
Young individuals were not miniature copies of adults: their skull proportions, teeth and jaw structures altered as they grew, providing evidence about feeding, development and life history.
More recently, researchers have even looked inside the skull using neutron tomography. This non-destructive imaging technique can reveal internal spaces associated with the brain, nerves and blood vessels without requiring anyone to dismantle a priceless Triassic cynodont—which is generally considered good museum manners.
Such studies help us to investigate sensory biology and the neurological evolution of non-mammalian cynodonts.
We cannot say exactly what covered the body of Massetognathus.
Close mammalian relatives are often reconstructed with whiskers or fur, but direct evidence for these features in this particular animal is lacking. It may have possessed some form of hair-like covering, or it may not have looked quite as cuddly as modern illustrations suggest.
Fossils give us bones and teeth with remarkable fidelity, but soft tissues frequently keep their secrets.
Even without an approved fluffiness rating, however, this specimen is irresistibly engaging.
Mounted upright at the Natural History Museum Abu Dhabi, the little skeleton seems to have paused in the middle of its 235-million-year journey to welcome us.
The pose may not represent how Massetognathus stood in life, but it succeeds in doing something important: it encourages us to stop, look closely and form a connection with an animal from a world almost beyond imagining.
Behind that appealing face is a beautifully adapted Triassic herbivore. Its strong jaws and broad teeth reveal increasingly sophisticated food processing. Its limbs preserve a stage in the changing locomotion of cynodonts. Its skull contributes to our understanding of brains and senses along the broader mammalian evolutionary line.
He may look as though he is waiting for friends, but Massetognathus pascuali has actually been waiting to tell us a much larger story—one about chewing, changing bodies and the wonderfully tangled family history that eventually produced mammals.
And after 235 million years, it would be rude not to say hello.
Scientific background: body-mass and dietary study in Acta Palaeontologica Polonica, original postcranial study archived by the Biodiversity Heritage Library, and recent traversodontid research and references from the Asociación Paleontológica Argentina.
Lead Image: Asset id: 2757017201. Abu Dhabi UAE 8th Feb 2026: A Massetognathus pascuali fossil at the Natural History Museum Abu Dhabi highlights this Triassic cynodont and its role in early mammal evolution
