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Related Experiment Videos

The earliest known eutherian mammal.

Qiang Ji1, Zhe-Xi Luo, Chong-Xi Yuan

  • 1Chinese Academy of Geological Sciences, Beijing 100037, China.

Nature
|April 27, 2002
PubMed
Summary

A 125-million-year-old eutherian (placental) mammal fossil from China reveals early mammal diversity. This ancient eutherian fossil shows climbing adaptations, suggesting varied locomotion in early placental mammals.

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Area of Science:

  • Paleontology
  • Vertebrate Paleontology
  • Mammalogy

Background:

  • The fossil record of early eutherian (placental) mammals is sparse, particularly from the Early Cretaceous period.
  • Understanding the early evolution and diversification of eutherians is crucial for reconstructing mammalian evolutionary history.

Purpose of the Study:

  • To describe a newly discovered eutherian mammal fossil from the Lower Cretaceous Yixian Formation of China.
  • To determine the phylogenetic position and locomotor adaptations of this new fossil.
  • To infer the implications for early eutherian diversification and ecological niche partitioning.

Main Methods:

  • Fossil excavation and preparation.
  • Comparative anatomical analysis of skeletal features, particularly limb and foot morphology.

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  • Phylogenetic analysis to determine evolutionary relationships.

    • Main Results:

    • Discovery of a nearly complete eutherian skeleton dating to approximately 125 million years ago.
    • The fossil represents one of the oldest eutherian specimens with both skull and skeleton.
    • Phylogenetic analyses place this new eutherian at the root of the eutherian tree.
    • Unique limb and foot features indicate scansorial (climbing) and arboreal (tree-living) adaptations.
    • This contrasts with the terrestrial or cursorial (running) adaptations of other known Cretaceous eutherians.

    Conclusions:

    • The discovery pushes back the record of fossil eutherians with preserved skeletons by 40-50 million years.
    • It suggests a more diverse and earlier radiation of stem eutherians than previously estimated, predating molecular divergence estimates for extant placental superorders.
    • Early eutherian lineages exhibited diverse locomotor specializations, enabling adaptation to various ecological niches during the Cretaceous period.