Morganucodon
As a Morganucodon you would be about the size of a shrew, rustling through the undergrowth at night while dinosaurs owned the daytime.
Caves in Wales
Morganucodon lived around 205 to 200 million years ago, at the boundary of the Triassic and Jurassic. The name means ‘Glamorgan tooth’, because thousands of its teeth and jaw fragments were found in limestone fissures in south Wales, filled with sediment that washed in from the surrounding islands. Related species are known from China, Europe and North America. It was a mammaliaform – part of the group that includes true mammals and their closest extinct relatives – not a dinosaur. It is one of the earliest animals in this lineage known in such detail.
Between two jaw joints
Morganucodon was about 10 centimetres long, excluding its tail, and probably weighed some 30–90 grams. It had two jaw joints at once: the new mammalian joint and the old reptilian one, whose bones would later move into the middle ear and become the tiny bones we hear with. Its teeth were already differentiated into incisors, canines, premolars and molars, and were replaced only once, as in mammals. You would eat insects and other small invertebrates, and a 2014 study of jaw mechanics and tooth wear suggested it specialised in harder, crunchier prey such as beetles, while its neighbour Kuehneotherium went for softer insects.
A long life in the slow lane
A 2020 study of growth rings in the cementum of Morganucodon teeth indicated a lifespan of up to about 14 years, much longer than a modern shrew’s one to two. It seems to have grown and lived more like a reptile, with a slower metabolism than present-day mammals. Large eyes, a well-developed sense of smell and probably whiskers would help you navigate at night. The danger: small carnivorous dinosaurs and other predators, which made the night an attractive time to be awake.
