Milk teeth have been discovered in the fossil jaw of a juvenile Wareolestes rex, a species of mammal from the Middle Jurassic.
Scientists suggest adult females secreted milk on to a bare patch of skin for their young to lap up.
Nipples and suckling as seen in modern mammals had still to evolve when Wareolestes rex lived.
The two centimetre-long jaw was found on Skye in 2015 and is one of the most complete fossils of the early mammal to be found outside of China.
Single teeth of Wareolestes rex have previously been found in England.
Palaeontologists from National Museums Scotland in Edinburgh and the University of Oxford have been examining the fossil from Skye.
Using micro-CT scanning technology, they have identified milk teeth and, inside the jaw, adult teeth that had not erupted through the gums.
The scientists said this showed that Wareolestes rex replaced its teeth once, like humans and other modern mammals.
It had a set of milk teeth, followed by a set of adult teeth.
This pattern of tooth replacement was an important step in the evolution of mammals and is linked to the production of milk to feed young, the scientists said.
Elsa Panciroli, the PhD student who led the research of the fossil, said: "This is such an exciting discovery.
"It's one of the most complete Middle Jurassic mammal fossils described from Scotland.
"This was a juvenile animal that was losing its milk teeth and the permanent teeth were just breaking through the gums.
"Tooth replacement like this tells us this early mammal fed on milk provided by the parent until it grew to adult size."
She added: "Wareolestes would have cared for its young, which is a behaviour we associate with modern mammals."
Living in a period when dinosaurs were the dominant animal, Wareolestes rex were a large mammal for the time, with adults growing to the size of a guinea pig.
The method of Wareolestes rex delivery of milk to its young is similar to that of platypus.
During the Middle Jurassic, Skye was covered in lagoons and filled with turtles, crocodiles, pterosaurs and dinosaurs.
Mainland Scotland was an island surrounded by a semi-tropical sea filled with marine reptiles and ammonites.
Palaeontologists believe an animal that lived in what is now Skye 165 million years ago fed milk to its young.