Kingdom Animalia
Phylum Chordata
Class  ???
Order Therapsida
Suborder Cynodontia
Family Docodontidae
Genus Castorocauda
1st Species Castorocauda lutrasimilis
Other attributes
Time Range 164 mya
Location China
Name Meaning Beaver tail
Physical Dimensions 42.5 centimeters long
Dietary Classification Carnivore

Castorocauda is a docodontid therapsid synapsid from the Middle Jurassic of China. It was named in 2006 by Qiang Ji. It was one of the biggest Mesozoic mammalians, as well as one of the few specialized ones.


Castorocauda looked like a mix between a beaver and an otter. It had a somewhat slender, barrel-shaped body, 4 semi-erect legs with webbed toes, a long, flat, broad tail (similar to that of a beaver), and a mid-sized, conical head with small jaws. Most of its body (excluding its feet and tail) would have been covered in thick fur, while its tail and feet would have been covered in smooth skin.


Castorocauda was a predator, preying on fish and small invertebrates. Unlike the teeth of other mammals, its teeth had points aligned in a straight row, and were designed for getting a hold of slippery prey rather than grinding them into a paste.


Castorocauda had adaptations similar to modern beavers, like webbed feet and a flat, broad tail; this tells us that it would have spent about half of its time in the water. More notable tools that it had included sturdy, muscular forelegs, which would allow the cynodont to dig in a similar manner to the platypus, a mammal that is capable of both swimming and digging. Along with this, its front teeth were different from those of other mammals; instead of having 4 points packed together in a cube-like fashion, it had 3 points lining up together in a row; those teeth would have been similar to those of mesonychids like Mongolonyx and even those of seals. In general, Castorocauda would have been one of the most unique and specialized Mesozoic mammalians to exist; other specialized Mesozoic mammalians included the badger-like Repenomamus, the armadillo-like Fruitafossor, and the flying squirrel-like Volaticotherium.

In popular cultureEdit

Castorocauda was featured in the 3rd episode of the 2011 documentary Dinosaur Revolution, where it was chased by a pair of Guanlong. When cornered by the theropods, it was depicted as being able to spray a strong-smelling liquid at them, similar to a modern skunk.

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