In a new study, paleontologists used synchrotron X-ray tomography of annual growth in dental cementum from fossil mammals belonging to three Jurassic animal groups to elucidate the origin of mammalian growth patterns that are intrinsically linked to mammals being warm-blooded.
Jurassic forest mammals. Image courtesy of © Zhao Chuang.
“This is the first time we've been able to reconstruct the growth patterns of early mammals in such detail,” said Dr Elise Newnham, a postdoctoral researcher at Queen Mary, University of London and the University of Bonn.
“By studying the spacing and texture of these growth rings, we can not only tell us how fast they grew at different stages of their life, but also make inferences about their metabolism and overall lifespan.”
The study calls into question previous assumptions about the growth patterns of our mammalian ancestors and the idea that these animals may have grown in a way similar to modern mammals.
Instead, the study answers a question raised by similar recent studies of early mammalian ancestors: when did modern mammalian life cycles evolve?
The researchers found that the first signs of modern mammalian growth patterns — high growth rates in young animals that stop at puberty — began in the earliest true mammals about 130 million years ago, compared with relatively little change throughout their lives in previously evolved mammalian forms.
However, like mammals, these animals grow slower and live much longer than modern small mammals such as mice and mice, with a maximum lifespan of 8 to 14 years.
The timing of this change in growth rate, combined with changes in tree-ring structure, indicates when these animals reached puberty and possibly sexual maturity.
“These data suggest that while all living small mammals reach sexual maturity within a few months of birth, the earliest mammals took several years to reach sexual maturity, supporting the results of a recent study on one of our study animals. Cruxatodon” Dr Pam Gill, a researcher at the Natural History Museum and University of Bristol, said:
“What's more, we find that this long, drawn-out life history was common to early mammals throughout the Jurassic Period.”
“Our results suggest that distinctive mammalian life history traits, such as high metabolic rate and extended parental care, evolved gradually over millions of years,” Dr Newnham said.
“The Jurassic period appears to have been a pivotal period in this evolution.”
The researchers used a technique called synchrotron X-ray tomography to image tiny growth rings in fossilized root cementum, the bone tissue that attaches teeth to the jaw. These rings are similar to those found in trees, but on a microscopic scale.
By counting the growth rings and analysing their thickness and texture, they were able to reconstruct the growth patterns and lifespan of the extinct animals.
“This work is a great example of how new technologies are revolutionizing our understanding of the distant past,” said Professor Thomas Martin from the University of Bonn.
“By closely examining these fossilized teeth, we can gain valuable insight into the lives of organisms that lived millions of years ago.”
“We are incredibly excited to be involved in this project,” said researcher Dr Jen Bright, from the University of Hull.
“Putting Jurassic fossils in a particle accelerator (synchrotron) to reconstruct the past sounds like science fiction, but it's actually possible!”
of Investigation result Published in a journal Scientific advances.
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Ellis Newham others2024. Origin of mammalian growth patterns during the Jurassic mammalian radiation. Scientific advances 10(32); doi: 10.1126/sciadv.ado4555
Source: www.sci.news
