Morganucodon was a small, plantigrade animal.
The tail was moderately long.
According to Kemp (2005), "the skull was 2–3 cm in length and a presacral body length of about 10 cm [4 inches].
In general appearance, it would have looked like a shrew or mouse".
There is evidence that it had specialized glands used for grooming, which may indicate that, like present day mammals, it had fur.

Like present day mammals of similar size and presumed habit, Morganucodon was likely nocturnal and spent the day in a burrow.
There is no direct fossil evidence, but several lines of evidence point to a nocturnal bottleneck in the evolution of the mammal class, and almost all modern mammals of similar size to Morganucodon are still nocturnal.
Likewise, burrowing was widespread both in the cynodonts and in primitive mammals.
The logics of phylogenetic bracketing would make Morganucodon nocturnal and burrowing too.
Plant material from the conifer Hirmeriella was also found in the fissure fills, indicating Morganucudon lived in, or near, a forested area.

The diet appears to have been insects and other small animals, with a preference for hard prey such as beetles.
Like most modern mammal insectivores, it grew fairly quickly to adult size.
 Its eggs were probably small and leathery, a condition still found in monotremes.

The teeth grew in mammalian fashion, with deciduous teeth being replaced by permanent teeth that were retained throughout the rest of the animal's life.
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 very first animals to do so.
The molars in the adult had a series of raised humps and edges that fit into each other, allowing for efficient chewing.
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.

The metabolism of Morganucodon was significantly slower than that of comparably sized modern mammals, and it had a life-span similar to reptiles.
Thus it likely did not possess the endothermic metabolism as seen in current mammals.
Morganucodon was a small, plantigrade animal. The tail was moderately long. According to Kemp (2005), "the skull was 2–3 cm in length and a presacral body length of about 10 cm [4 inches]. In general appearance, it would have looked like a shrew or mouse". There is evidence that it had specialized glands used for grooming, which may indicate that, like present day mammals, it had fur.
Like present day mammals of similar size and presumed habit, Morganucodon was likely nocturnal and spent the day in a burrow. There is no direct fossil evidence, but several lines of evidence point to a nocturnal bottleneck in the evolution of the mammal class, and almost all modern mammals of similar size to Morganucodon are still nocturnal. Likewise, burrowing was widespread both in the cynodonts and in primitive mammals. The logics of phylogenetic bracketing would make Morganucodon nocturnal and burrowing too. Plant material from the conifer Hirmeriella was also found in the fissure fills, indicating Morganucudon lived in, or near, a forested area.
The diet appears to have been insects and other small animals, with a preference for hard prey such as beetles. Like most modern mammal insectivores, it grew fairly quickly to adult size.  Its eggs were probably small and leathery, a condition still found in monotremes.
The teeth grew in mammalian fashion, with deciduous teeth being replaced by permanent teeth that were retained throughout the rest of the animal's life. 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 very first animals to do so. The molars in the adult had a series of raised humps and edges that fit into each other, allowing for efficient chewing. 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.
The metabolism of Morganucodon was significantly slower than that of comparably sized modern mammals, and it had a life-span similar to reptiles. Thus it likely did not possess the endothermic metabolism as seen in current mammals.
Morganucodon