Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth

Nature
Eva A Hoffman, Timothy B Rowe

Abstract

Transformations in morphology, physiology and behaviour along the mammalian stem lineage were accompanied by profound modifications to reproduction and growth, including the emergence of a reproductive strategy characterized by high maternal investment in a small number of offspring1,2 and heterochronic changes in early cranial development associated with the enlargement of the brain3. Because direct fossil evidence of these transitions is lacking, the timing and sequence of these modifications are unknown. Here we present what is, to our knowledge, the first fossil record of pre- or near-hatching young of any non-mammalian synapsid. A large clutch of well-preserved perinates of the tritylodontid Kayentatherium wellesi (Cynodontia, Mammaliamorpha) was found with a presumed maternal skeleton in Early Jurassic sediments of the Kayenta Formation. The single clutch comprises at least 38 individuals, well outside the range of litter sizes documented in extant mammals. This discovery confirms that production of high numbers of offspring represents the ancestral condition for amniotes, and also constrains the timing of a reduction in clutch size along the mammalian stem. Although tiny, the perinates have an overall skull shape that is...Continue Reading

References

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Citations

Sep 12, 2019·Evolution & Development·David Jablonski
Oct 28, 2019·Nature·John Pickrell
Oct 14, 2020·Nature Communications·Elis NewhamIan J Corfe
Oct 14, 2020·Proceedings of the National Academy of Sciences of the United States of America·Tomasz SulejGrzegorz Niedźwiedzki
Jan 20, 2022·Proceedings. Biological Sciences·Stewart M EdieDavid Jablonski

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Methods Mentioned

BETA
X-ray

Software Mentioned

smatr
VGStudio Max
R

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