Jurassic fossil juvenile reveals prolonged life history in early mammals

Living mammal groups exhibit rapid juvenile growth with a cessation of growth in adulthood1. Understanding the emergence of this pattern in the earliest mammaliaforms (mammals and their closest extinct relatives) is hindered by a paucity of fossils representing juvenile individuals. We report except...

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Bibliographic Details
Published inNature (London) Vol. 632; no. 8026; pp. 815 - 4
Main Authors Panciroli, Elsa, Benson, Roger B J, Fernandez, Vincent, Fraser, Nicholas C, Humpage, Matt, Luo, Zhe-Xi, Newham, Elis, Walsh, Stig
Format Journal Article
LanguageEnglish
Published London Nature Publishing Group 22.08.2024
Subjects
Body mass
Cementum
Computed tomography
Dentition
Early experience
Fossils
Jurassic
Life history
Life span
Macroevolution
Mammals
Marsupials
Mesozoic
Metabolism
Synchrotron radiation
Teeth
Tomography
X ray imagery
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Summary:Living mammal groups exhibit rapid juvenile growth with a cessation of growth in adulthood1. Understanding the emergence of this pattern in the earliest mammaliaforms (mammals and their closest extinct relatives) is hindered by a paucity of fossils representing juvenile individuals. We report exceptionally complete juvenile and adult specimens of the Middlejurassic docodontan Krusatodon, providing anatomical data and insights into the life history of early diverging mammaliaforms. We used synchrotron X-ray micro-computed tomography imaging of cementum growth increments in the teeth2-4 to provide evidence of pace of life in a Mesozoic mammaliaform. The adult was about 7 years and the juvenile 7 to 24 months of age at death and in the process of replacing its deciduous dentition with its final, adult generation. When analysed against a dataset of life history parameters for extant mammals5, the relative sequence of adult tooth eruption was already established in Krusatodon and in the range observed in extant mammals but this development was prolonged, taking place during a longer period as part of a significantly longer maximum lifespan than extant mammals of comparable adult body mass (156 g or less). Our findings suggest that early diverging mammaliaforms did not experience the same life histories as extant small-bodied mammals and the fundamental shift to faster growth over a shorter lifespan may not have taken place in mammaliaforms until during or after the Middlejurassic.
ISSN:0028-0836
1476-4687
DOI:10.1038/s41586-024-O7733-1