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Unravelling eutherian and metatherian divergence through dental evolution
Haibing Wang1,2, Thomas Martin3, Jukka Jernvall4,5
1Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences , Beijing, People's Republic of China.
Proceedings. Biological Sciences
|January 15, 2026
Summary
The evolution of mammal teeth shows distinct paths for eutherians (placental mammals) and metatherians (marsupials). Eutherians lost a molar, while metatherians lost premolars from a common ancestor's dental formula.
Area of Science:
- Paleontology
- Evolutionary Biology
- Mammalian Evolution
Background:
- Therian mammals represent a major evolutionary transition in vertebrates.
- Tribosphenic molars are key innovations in eutherian (placental) and metatherian (marsupial) mammals.
- The evolutionary pathways of dental transformations in early therians remain challenging to elucidate.
Purpose of the Study:
- To detail the morphology of the early eutherian mammal, Acristatherium.
- To reconstruct ancestral dental formulae at key evolutionary nodes (Theria, Eutheria, Metatheria).
- To refine models explaining dental transformations in early therians.
Main Methods:
- Detailed morphological analysis of Acristatherium fossils.
- Reconstruction of ancestral dental formulae using palaeontological data.
- Integration of developmental criteria with palaeontological evidence.
- Testing hypotheses of serial homology versus independent premolar-molar development.
Main Results:
- Identified distinct dental formulae at key nodes of Eutheria, Metatheria, and Theria.
- Refined the premolar-molar independence model, challenging serial homology hypotheses.
- Eutherians lost the distal molar, while metatherians lost premolars from a common ancestor with 5 premolars and 4 molars.
Conclusions:
- Dental evolution in therian mammals involved independent experimentation in premolar and molar development.
- Distinct evolutionary paths (molar loss in eutherians, premolar loss in metatherians) diverged from a common ancestor.
- Conserved genetic and developmental mechanisms underlie the observed phenotypic diversity in mammalian dentition.
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