Studying fossils shows that early mammals grew more slowly and lived longer, helping us understand their evolutionary development. What differentiated the growth and development patterns of early mammals in the Jurassic period? This question was investigated jointly by researchers from Queen Mary University of London and the University of Bonn.

By studying the growth rings in fossilized tooth roots, paleontologists have been able to estimate the lifespan of these ancient animals, their growth rates, and even when they reached sexual maturity.

“Never before have we been able to reconstruct the growth patterns of these early mammals in such detail,” says lead author Dr. Alice Newham, a postdoctoral researcher at Queen Mary University of London and Alexander von Humboldt Research Fellow at the University of London, Bonn. at the time of the research.

Uncovering historical growth patterns

In a study recently published in the journal Science Developments The team analysed fossilised tooth roots from mammal species from the Early Jurassic to Late Jurassic (200 to 150 million years ago) from three separate sites. The finds from Wales represent some of the earliest known precursors of Early Jurassic mammals, while fossils from Oxfordshire, UK, represent a wide range of early mammals living together. Fossils from a third site in Portugal date to the Late Jurassic.

Articles from Advanced Imaging

The research team examined the fossils using a technique called synchrotron X-ray tomography, in which electrons are accelerated to near the speed of light (unlike traditional X-ray imaging). This technique has several advantages: the fossils no longer need to be prepared (i.e. dissected) to be analyzed as a whole. The images obtained with synchrotron X-ray tomography are also of higher quality than those obtained with traditional X-ray microtomography.

The researchers were able to image tiny growth rings in fossilized root cementum, the bone tissue that connects the teeth to the jaw. “The rings are similar to tree rings, but on a microscopic level,” explains senior author Professor Thomas Martin from the Vertebrate-Mammal Working Group at the Institute of Organismal Biology at the University of Bonn. “Counting the rings and analyzing their thickness and texture allowed us to reconstruct the growth and lifespan of these extinct animals.”

The researchers found that the first signs of growth patterns characteristic of modern mammals, such as the adolescent growth spurt, began to appear around 150 million years ago. Early mammals grew much more slowly but lived much longer than modern small mammals, with lifespans of eight to 14 years, compared to the one or two years of modern mice, for example. However, early mammals took years to reach puberty, unlike their modern descendants, who reach puberty in just a few months.

Conclusions about mammalian evolution

Dr Alice Newham explains: “Our findings suggest that characteristic mammalian life patterns, characterised by, for example, high metabolic rates and long parental care phases, evolved over millions of years. The Jurassic period appears to have been a crucial period for this change.”

Besides Queens University of London and the University of Bonn, research partners also included the University of Helsinki, the Geological Survey of Finland, the Natural History Museum (Great Britain), the University of Hull (Great Britain), the European Synchrotron Centre for Radiation (France), the University of Southampton (Great Britain), the College of Osteopathic Medicine (USA), the University of Bristol (Great Britain) and the University of Edinburgh (Great Britain).

The research was made possible with funding from the European Community’s Seventh Framework Programme, students from the Engineering and Physical Sciences Research Council, an Alexander von Humboldt Research Fellowship awarded to Dr. Alice Newham, the Paul Scherrer Institute, the Academy of Finland, Gingko Investments LTD and Versus Arthritis grant 23115.