Scientists Analyze Fossils of Mouse-Like Mammal That Existed With Dinosaurs, Find Major Growth Transformation

It is no secret that mammals, as well as several other groups of animals, have undergone extreme changes over millennia. These transformations have not just been physical but also in terms of lifestyle. This difference was noted in two sets of fossils from Scotland's Isle of Skye, stated Phys.org. Findings regarding these remains have been published in the journal Nature.

These fossils belonged to Docodonta, an early order of small mammals. Past examinations have claimed that they were the size of a mouse, and the remains analyzed in this study belonged to a being that lived during the Middle Jurassic and coexisted with dinosaurs. One set of fossils belonged to adult Krusatodons kirtlingtonensis, while the other was juvenile. The adult specimen was unearthed in 1972, while the juvenile was discovered in 2016. Scientists believe that smaller mammals have a much higher pace of growth until they reach the stage of maturity. They were also assumed to have shorter life spans and, hence, reproduced many offspring to ensure survival. 

Finding an adult and juvenile specimen of the same species was a rare occurrence, stated New Scientist. It opened a lot of new avenues for researchers. "It meant that we could start asking questions we couldn’t have dreamt of with just one specimen," said Elsa Panciroli at the National Museum of Scotland.

Examinations of these fossils, however, showcase that this possibly was not always the case. The results indicate that these small mammals underwent development slowly and went on to live long life spans. Both sets of fossils have been dated back to around 166 million years ago. The adult specimen was aged seven years at the time of death, while the juvenile was 7 to 24 months when they took their last breath. The adult weighed close to 58 grams, while the young one was a little more than half of that. 

Researchers focused on the incremental growth of teeth in these remains, which gave them information about the creatures' age and weight. The team also noted that the young one was in the process of replacing their milk teeth with adult teeth. "That was quite surprising because this animal is about the size of a squirrel or shrew," said Panciroli. "We would expect it to be replacing its teeth much earlier – within weeks or months. So we knew immediately that it must have grown very differently [than modern species]."

Further analysis showcased that the juvenile's age for reaching maturity was going to be more than what is noticed for modern small mammals of similar size. The species took two years to wean from its mother, a period which gets over in a handful of weeks for modern small mammals. This implies that there was a longer development period and, therefore, a longer lifespan. Researchers want to examine more small mammals from the period to confirm if this growth pattern was widespread or exclusive only to the Krustodons. "Hopefully, in years to come, we’ll find more fossils or new methods of asking those questions," Panciroli said.