What sets apart the growth and development patterns of early mammals from the Jurassic era? This question has been explored by researchers at Queen Mary University of London and the University of Bonn. By examining growth rings in fossilized tooth roots, paleontologists have been able to estimate the lifespans, growth rates, and the age at which these ancient creatures reached sexual maturity. The findings have been published in the journal Science Advances.
“For the first time, we have managed to reconstruct the growth patterns of these early mammals in unprecedented detail,” says the lead author Dr. Elis Newham, who was a postdoctoral fellow at Queen Mary University of London while conducting this study as an Alexander von Humboldt Research Fellow at the University of Bonn, until March 31, 2024.
The research team examined fossilized tooth roots from mammal species that existed during the Early to Late Jurassic periods (200-150 million years ago), sourced from three distinct locations. The fossils discovered in Wales are among the earliest known mammal precursors from the Early Jurassic, while those found in Oxfordshire, UK, represent a wide variety of early mammals coexisting at that time. The third set of fossils from Portugal dates to the Late Jurassic period.
X-ray Imaging of Fossil Tooth Roots
The researchers employed synchrotron X-ray tomography, a sophisticated imaging technique that accelerates electrons to nearly the speed of light, rather than relying on traditional X-ray imaging methods. This approach offers several benefits, including the ability to analyze fossils without the need to slice them for examination. Additionally, the quality of images obtained using synchrotron X-ray tomography surpasses that of conventional X-ray microtomography.
The team was able to visualize minute growth rings in the fossilized root cement — the bony material that secures the teeth to the jaw. “These rings are akin to those seen in trees, but much smaller,” explains Professor Thomas Martin from the Vertebrates — Mammals group at the University of Bonn’s Institute of Organismic Biology, who is a senior author on the paper. “By counting these rings and assessing their thickness and texture, we could deduce the growth patterns and lifespans of these long-extinct species.”
The researchers found that the earliest indications of growth patterns typical of modern mammals, such as a significant growth spurt during puberty, began to appear around 150 million years ago. These early mammals exhibited slower growth rates but enjoyed much longer lifespans than present-day small mammals, living around eight to fourteen years, compared to just one or two years typical for modern mice. Furthermore, reaching sexual maturity took several years for these early mammals, unlike their modern counterparts that mature within a few months.
“Our research indicates that the unique life history characteristics of mammals, marked by elevated metabolic rates and prolonged parental care phases, likely developed over millions of years,” Dr. Elis Newham notes. “The Jurassic period seems to have been a pivotal time for these evolutionary changes.”
Collaboration and Funding
The study involved collaboration not only with Queen Mary University of London and the University of Bonn but also with the University of Helsinki, the Geological Survey of Finland, the Natural History Museum (UK), the University of Hull (UK), the European Synchrotron Radiation Facility (France), the University of Southampton (UK), the College of Osteopathic Medicine (USA), the University of Bristol (UK), and the University of Edinburgh (UK).
This research was funded through various sources, including the European Community’s Seventh Framework Programme, Engineering and Physical Sciences Research Council studentships, an Alexander von Humboldt Research Fellowship awarded to Dr. Elis Newham, as well as support from the Paul Scherrer Institute, the Academy of Finland, Gingko Investments LTD, and Versus Arthritis Grant 23115.
