Docodonta is an order of extinct Mesozoic mammaliaforms (advanced cynodonts closely related to true crown-group mammals).

They were among the most common mammaliaforms of their time, persisting from the Middle Jurassic to the Early Cretaceous across the continent of Laurasia (modern-day North America, Europe, and Asia).

Chinese docodontans include otter-like,[4] mole-like,[5] and squirrel-like species,[6][7] hinting at impressive ecological diversity within the group.

Like true mammals, docodontans have hair,[4] a saddle-shaped hyoid apparatus,[7] and reduced postdentary jaw bones which are beginning to develop into middle ear ossicles.

On the other hand, the postdentary bones are still attached to the jaw and skull, the nares (bony nostril rims) have yet to fuse, and in most species the spine's thoracic-lumbar transition is rather subdued.

The ectotympanic bone, also known as the angular, fits into a deep slot on the dentary which opens backwards, a characteristic unique to docodontans.

The incus (also known as the quadrate) is still relatively large and rests against the petrosal bone of the braincase, a remnant of a pre-mammalian style jaw joint.

In true mammals, the postdentary elements detach fully and shrink further, becoming the ossicles of the middle ear and embracing a circular eardrum.

The snout is long and has several plesiomorphic traits: the nares (bony nostril holes) are small and paired, rather than fused into a single opening, and the rear edge of each naris is formed by a large septomaxilla, a bone which is no longer present in mammals.

The frontal and parietal bones of the skull roof are flat and broad, and there is no postorbital process forming the rear rim of the orbit (eye socket).

Microdocodon has a straight, sideways-oriented basihyal which connects to two pairs of bony structures: the anterior hyoid cornu (a jointed series of rods which snake up to the braincase), and the posterior thyrohyals (which link to the thyroid cartilage).

[5][6][7][11] The only known specimen of Castorocauda has a pointed spur on its ankle, similar to defensive structures observed in male monotremes and several other early-branching mammals.

[2] Docodontans and other Mesozoic mammals were traditionally thought to have been primarily ground dwelling and insectivorous, but recent more complete fossils from China have shown this is not the case.

Castorocauda had a flattened tail, similar to that of a beaver, and recurved molar cusps, which suggests a possible diet of fish or aquatic invertebrates.

Docofossor shows many of the same physical traits as the modern day golden mole, such as wide, shortened digits in the hands for digging.

[5] A 2024 study on adult and juvenile Krusatodon specimens found that docodontans had a slower metabolism and lower growth rates relative to modern mammals of the same size.

The closest comparisons among modern mammals were monotremes and hyraxes, though Krusatodon was much smaller than either, at fewer than 156 g in adult body mass.

Previously, docodontans were sometimes regarded as belonging to Mammalia, owing to the complexity of their molars and the fact that they possess a dentary-squamosal jaw joint.

Monographs by George Gaylord Simpson in the 1920s argued that they were specialized "pantotheres", part of a broad group ancestral to true therian mammals according to their complex molars.

He drew comparisons to the teeth of Morganucodon and other "triconodont" mammaliaforms, which had fairly simple lower molars with a straight row of large cusps.

[1] Another proposed docodontan relative, Tikitherium from India, was originally considered to have been a very early mammaliaform which lived during the Carnian stage of the Triassic.

[34] Some authors have suggested splitting Docodonta into two families (Simpsonodontidae and Tegotheriidae),[35][14][36] but the monophyly of these groups (in their widest form) are not found in any other analyses, and therefore not accepted by all mammal palaeontologists.

[37] Cladograms based on phylogenetic analyses focusing on docodontan relationships: Morganucodonta Gondtherium Tikitherium Castorocauda Tashkumyrodon Dsungarodon Borealestes Haldanodon Docodon Docofossor Itatodon Simpsonodon Agilodocodon Krusatodon Sibirotherium Hutegotherium Microdocodon Tegotherium Sinoconodon Morganucodon Dinnetherium Megazostrodon Kuehneotherium Delsatia Woutersia Gondtherium Tikitherium Hutegotherium Sibirotherium Tegotherium Agilodocodon Krusatodon Simpsonodon Itatodon Tashkumyrodon Castorocauda Dsungarodon Dobunnodon Borealestes Docofossor Docodon Haldanodon