Fossil Hints That Jurassic Mammals Lived Slow and Died Old

Researchers have discovered a pair of fossilized skeletons of a Jurassic mammal, Krusatodon kirtlingtonensis, which suggest that these small mammals lived longer and grew more slowly than their modern relatives. The fossils, found on the Isle of Skye in Scotland, date back 166 million years and provide a more complete understanding of this species, which was previously known only from teeth. The larger specimen, discovered in the 1970s, and a juvenile found in 2016, represent an adult and a juvenile of the same species. High-resolution CT scans and analysis of dental cementum rings revealed that the adult was approximately 7 years old at death, while the juvenile was between 7 months and 2 years old, still in the process of replacing its baby teeth. This extended tooth replacement period is unusual for small mammals, which typically lose baby teeth within months. The findings indicate that Krusatodon had a longer lifespan and slower growth rate, resembling modern mammals like hyraxes. The study suggests that early Mesozoic mammals may have experienced prolonged growth throughout their lives, contrasting with the rapid growth seen in many contemporary small mammals. The research highlights the need for more fossil discoveries from this era to better understand the evolutionary trajectory of mammals and their eventual dominance in various ecosystems.