Published:
08.08.2024 10:32:00
.jpg "Researchers use X-ray images to decipher the secrets of Jurassic mammals")
Digital reconstruction of Dryolestes (left) and Haldanodon (right), two creatures from the Late Jurassic period, by British paleoartist James Brown, in consultation with Pamela G. Gill, one of the authors. Copyright Pamela G. Gill.
A new study published in Science Advances reveals how early mammals grew and evolved during their crucial radiation in the Jurassic period.
Using a technique called synchrotron X-ray tomography, researchers were able to image growth rings in fossilized tooth roots and thus estimate the lifespan, growth rate and even the time of sexual maturity of these ancient creatures.
“This is the first time we have been able to reconstruct the growth patterns of these early mammals in such detail,” says Dr. Elis Newham, postdoctoral fellow at Queen Mary University of London and Alexander von Humboldt Research Fellow at the University of Bonn, lead author of the study.
“By examining the spacing and nature of these growth rings, we can not only determine how quickly they grew at different stages of life, but also draw conclusions about their metabolism and their overall life history.”
Dr Neil Gostling, Associate Professor of Evolution and Palaeobiology at the University of Southampton and co-author of the study, said: “It is truly amazing how technology, particularly computed tomography, has enabled us to extract every single element of data from these remarkable fossils.
“Paleontology is no longer a Victorian science that digs in the dirt or describes curiosities in museum collections – although that is fun. It is a modern science that explains the life stories of these animals in great detail.”
The results challenge previous assumptions about the growth patterns of mammalian ancestors and suggest that these animals may have grown more similarly to modern mammals. Instead, this article answers the question raised in similar recent studies of early mammal ancestors: “When did the life history of modern mammals evolve?”
The researchers found that the first signs of the growth pattern of modern mammals – high growth rates in young animals that stop at puberty – emerged in the earliest true mammals about 130 million years ago. The earlier-evolving “mammalian forms” experienced comparatively little change over the course of their lives.
However, like mammalian species, early mammals grew more slowly and lived much longer than today’s small mammals such as rats and mice, reaching a maximum lifespan of between eight and 14 years. The timing of this change in growth rate, as well as changes in the structure of the growth rings, indicate when these animals went through puberty and possibly reached sexual maturity.
“These data suggest that while living small mammals reach sexual maturity within a few months of birth, the earliest mammals took several years to reach sexual maturity. This confirms recent findings for one of our studied animals, Krusatodon,” said Dr. Pam Gill, co-leader of the study and research associate at the Natural History Museum London and the University of Bristol.
“We also find that this long, extended life history was common among early mammals throughout the Jurassic period.”
Dr. Newham explains: “These results suggest that mammals’ unique life histories, such as high metabolism and extensive parental care, evolved gradually over millions of years. The Jurassic period appears to be a key period in this evolution.”
CT “slice” of a fossilized tooth root of the Upper Jurassic mammal species Haldanodon.
The research team used a technique called synchrotron X-ray tomography to image tiny growth rings in fossilized root cement, the bone tissue that connects teeth to the jaw. These rings are similar to those found in trees, but are microscopic. By counting the rings and analyzing their thickness and texture, the researchers were able to reconstruct the growth patterns and lifespan of these extinct animals.
“This study is a great example of how new technologies are revolutionizing our understanding of the deep past,” says Professor Thomas Martin of the University of Bonn, one of the study’s lead authors. “By studying these fossilized teeth, we can gain valuable insights into the lives of creatures that lived millions of years ago.”
Dr Jen Bright, co-author of the study and head of the Zoology course at the University of Hull, added: “It has been so exciting to be involved in this project. Putting Jurassic fossils into a particle accelerator (the synchrotron) and using them to reconstruct the past sounds like science fiction, but we can actually do it!”
Members of Queen Mary University of London, the University of Southampton, the University of Bonn, the Natural History Museum London, the University of Helsinki, the Geological Survey of Finland, the University of Hull, the European Synchrotron Radiation Facility (France), the College of Osteopathic Medicine (USA), the University of Bristol and the University of Edinburgh participated in this study.
The origins of mammal growth patterns during the Jurassic mammal radiation
is published in
Scientific advances
and is available online.
