In new research, paleontologists used synchrotron X-ray tomography of annual growth increments in the dental cementum of fossil mammals from three faunas across the Jurassic period to map the origin of patterns of mammalian growth patterns, which are intrinsically related to mammalian warm-bloodedness.
“This is the first time we’ve been able to reconstruct the growth patterns of these early mammals in such detail,” said Dr. Elis Newham, 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 how fast they grew at different stages of life, but also make inferences about their metabolism and overall life history.”
The current study challenges previous assumptions about the growth patterns of mammal ancestors and suggestions that these animals may have grown more similarly to modern mammals.
Instead, the study answers the question posed by similar recent studies of early mammal ancestors: When did the modern mammal life history evolve?
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 comparison with relatively little change through life in earlier evolving mammaliaforms.
However, like mammaliaforms, these animals still grew more slowly and lived for much longer than living 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.
“These data suggest 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…
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