Secrets of the Jurassic: Primitive mammals with incredible longevity discovered
Ancient mammals, which lived in the Middle Jurassic and weighed less than 100 grams as adults, appear to have followed a slower and more prolonged growth path than modern one.
According to a recent research published in Nature, primitive mammals may have lived longer than their modern descendants of similar body mass. This discovery, based on the analysis of fossils found in Scotland dating back to the Middle Jurassic (about 166 million years ago), offers new insights into the development and lifespan of early mammals.
Growth and Longevity of Mammals
Understanding the growth and longevity of mammals has always been one of the most fascinating challenges for paleontologists and evolutionary scholars. Modern mammals, as we know, follow a developmental pattern that has been well-documented through extensive studies. This pattern involves rapid growth in the early years of life, followed by the cessation of growth upon reaching adulthood.
This seemingly simple scheme is based on a balanced combination of genetic, environmental, and behavioral factors that determine the maturation and lifespan of each species. However, new research is now challenging this linear view, suggesting that primitive mammals – the mammaliaformes – may have had a significantly different life trajectory.
These ancient mammals, which lived in the Middle Jurassic and weighed less than 100 grams as adults, seem to have followed a much slower and prolonged growth path, with a lifespan far exceeding that of similarly sized modern mammals. This hypothesis is based on a detailed analysis of recently discovered fossils and offers new perspectives on the evolution of life strategies in mammals.
Fossil Discovery: Krusatodon kirtlingtonensis
The discovery represents a significant step forward in our understanding of the paleobiology of mammals. On the Isle of Skye in Scotland, researchers found partial skeletons of docodonts, a subclass of mammaliforms from the Middle Jurassic, belonging to the species Krusatodon kirtlingtonensis.
This discovery is particularly important because juvenile mammal fossils are extremely rare and provide crucial information about the early developmental stages of these creatures. By analyzing dental growth increments, researchers determined that the adult specimen was about 7 years old at the time of death, a considerable age for an animal of such size. The juvenile, on the other hand, was between 7 and 24 months old and was in the process of replacing its milk teeth with permanent ones. This teething process is a key indicator of biological maturation and allows researchers to trace the growth rate of the species.
Measurements of limb bones and tooth sizes revealed that the adult weighed between 58 and 158 grams, while the juvenile represented 51-59% of the adult's body mass. These data suggest that Krusatodon kirtlingtonensis had a prolonged growth rate, different from that of similarly sized modern mammals, and that this slow growth was accompanied by a longer lifespan.
The Study
The analysis is based on cutting-edge methodologies that combine traditional paleontological techniques with advanced imaging and analytical technologies. The fossil teeth, in particular, were subjected to microscopic analysis to identify annual growth increments, similar to the growth rings of trees.
This technique, known as dental microstratigraphy, allows for the precise determination of the individuals' ages at the time of death and the reconstruction of their growth rates. Additionally, measurements of the forelimb and thigh bones were used to estimate body mass and the degree of musculoskeletal development of the specimens.
These measurements, compared with those of similarly sized modern mammals, revealed a significantly slower growth rate for Krusatodon kirtlingtonensis. This prolonged growth, associated with an extended lifespan, suggests that primitive mammals may have adopted different life strategies to cope with the environmental and ecological challenges of the Middle Jurassic.
Mammals Coexisted with Dinosaurs
The implications of this discovery are vast and profound, shedding new light on how primitive mammals might have lived and thrived in a world dominated by dinosaurs. The slow growth and greater longevity of Krusatodon kirtlingtonensis suggest that these ancient mammals had more flexible and adaptive life strategies compared to their modern descendants.
In an environment characterized by intense competition for resources and the presence of numerous predators, slow growth might have allowed these mammals to develop more effective defenses and more complex behaviors. Additionally, a longer life would have offered greater opportunities for reproduction and parental care, increasing the chances of survival for younger generations. This discovery challenges the traditional notion that small body mass in mammals is always associated with a short life and rapid reproduction. Instead, it suggests that early mammals might have had a broader range of life strategies, allowing them to occupy diverse ecological niches and evolve more dynamically.
