Morganucodon ("Glamorgan tooth") is an early mammaliaform genus that lived from the Late Triassic to the Middle Jurassic.

Unlike many other early mammaliaforms, Morganucodon is well represented by abundant and well preserved (though in the vast majority of cases disarticulated) material.

In 1949, Walter Georg Kühne noted the lower cheek tooth of a primitive mammal while examining samples of the rock.

[8] In 2016 Percy Butler and Denise Sigogneau-Russell named the species Morganucodon tardus from an upper right molar (M34984) collected from the Watton Cliff locality near Eype in Dorset, England, dating to the late Bathonian stage of the Middle Jurassic.

Plant material from the conifer Hirmeriella was also found in the fissure fills, indicating Morganucudon lived in, or near, a forested area.

[19] The combination of rapid growth in juveniles and a toothless stage at infancy strongly suggests that Morganucodon raised its young by lactation; indeed, it may have been among the first animals to do so.

However, unlike the situation in most later mammals, the upper and lower molars did not occlude properly when they first met; as they wore against each other, however, their shapes were modified by wear to produce a precise fit.

[21] A 2020 study suggests that the metabolism of Morganucodon was significantly slower than that of comparably sized modern mammals, and that it had a life-span more similar to that of reptiles, with the oldest specimen having a lifespan of 14 years.

Nevertheless, its lower jaw retains some of the bones found in its non-mammalian ancestors in a very reduced form rather than being composed solely of the dentary.

[26] Morganucodon also suckled (it may have been the earliest animal to do so), had only two sets of teeth and grew rapidly to adult size and stopped growing thereafter, all typical mammalian traits.