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Researchers unlock life history secrets of Jurassic mammals using X-ray imaging
Modern mammal growth patterns were found to originate around 130 million years ago
- Dental growth rings reveal dramatic differences in growth patterns between ancient and modern mammals
- Modern mammal growth patterns were found to originate around 130 million years ago
- The study was made possible with the Natural History Museum’s vast Mesozoic mammal collections
A new study reveals how early mammals grew and developed during their pivotal Jurassic radiation. Using the exceptional collection of Mesozoic jaws and teeth at the Natural History Museum London, and by applying cutting-edge scanning techniques to image growth rings in fossilised tooth roots, researchers were able to estimate lifespans, growth rates, and even the timing of sexual maturity in these ancient creatures.
The findings challenge previous assumptions about the growth patterns of mammal ancestors, and suggestions that these animals may have grown more similarly to modern mammals. Instead, this paper answers the question of when modern mammal life history evolved.
The researchers found that the first signs of the modern mammal growth pattern – high growth rates in young animals that are arrested at puberty – originated amongst the earliest true mammals around 130 million years ago.
In earlier evolving “mammaliaforms” there was comparatively little change through life. However, like mammaliaforms, early mammals still grew more slowly and lived for much longer than today’s small mammals like rats and mice, reaching maximum lifespans anywhere between eight to 14 years-of-age.
The timing of this growth rate change, alongside changes in the structure of growth rings, indicates when these animals underwent puberty, and potentially when they became sexually mature.
Dr Pam Gill, co-lead of the study and Scientific Associate at the Natural History Museum London and University of Bristol, commented: “This data suggests that while living small-bodied mammals are sexually mature within months from birth, the earliest mammals took several years to reach sexual maturity, corroborating recent findings for one of our studied animals, Krusatodon.
“We further find here that this long, drawn out life history was common amongst early mammals all the way through the Jurassic.”
Dr Elis Newham, of Queen Mary University of London, and first author of the study, commented: "This is the first time we've been able to reconstruct the growth patterns of these early mammals in such detail.
"By studying the spacing and texture of these growth rings, we can not only tell how fast they grew at different stages of life, but also make inferences about their metabolism and overall life history."
The research team used a technique called synchrotron X-ray tomography to image tiny growth rings in fossilized root cementum, the boney tissue attaching teeth to the jaw. These rings are similar to those found in trees, but on a microscopic scale. By counting the rings and analyzing their thickness and texture, the researchers were able to reconstruct the growth patterns and lifespans of these extinct animals.
"These results suggest that the unique life history traits of mammals, like high metabolic rates and extended parental care, evolved gradually over millions of years," explains Dr Newham. "The Jurassic period appears to be a pivotal time in this evolution."
Dr Pam Gill added: “What I find so exciting is that these Mesozoic mammal collections in the NHM were collected many years ago, and the bones and teeth described and studied, but they still have much to tell us when combined with high-resolution scanning; the trips to the synchrotrons are long shifts, but the results are very exciting!”
This paper 'The origins of mammal growth patterns during the Jurassic mammalian radiation', was published today in Science Advances. The paper can be accessed here.
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