Acristatherium (Cretaceous eutherian) dental morphology and therian evolution + post K-Pg mammals
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Ben Creisler
Dec 18, 2025, 6:20:41 PM12/18/25
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Ben Creisler
Mammal papers:
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eLife Assessment
This important study fills a major geographic and temporal gap in understanding Paleocene mammal evolution in Asia and proposes an intriguing "brawn before bite" hypothesis grounded in diverse analytical approaches. However, the findings are incomplete because limitations in sampling design - such as the use of worn or damaged teeth, the pooling of different tooth positions, and the lack of independence among teeth from the same individuals - introduce uncertainties that weaken support for the reported disparity patterns. The taxonomic focus on predominantly herbivorous clades also narrows the ecological scope of the results. Clarifying methodological choices, expanding the ecological context, and tempering evolutionary interpretations would substantially strengthen the study.
Abstract
The first 10 million years (Myr) following the Cretaceous-Paleogene (K-Pg) mass extinction marked a period of global greenhouse conditions and dramatic rise of placental mammals. Because ∼80% of known terrestrial sections capturing post-K-Pg mammal recovery come from North America, a substantial knowledge gap exists in the tempo and mode of recovery in Asia, where only 3% of sites are located and most contain species found nowhere else. We show that isolated Paleocene placental assemblages from China (1) reached high tooth size disparity early in the Paleocene, (2) tracked regional and global environmental changes in their dental shape later in the Paleocene, and (3) achieved maximum dental shape-performance integration near the end of the first 10 Myr post-K-Pg. This ‘brawn before bite’ transformation, coupled with prolonged dental shape versus performance variability, favors a scenario whereby many living orders of placental mammals were borne out of phenotypically and functionally plastic ancestral assemblages, including those in tropical south China, during the Paleocene.
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Haibing Wang, Thomas Martin, Jukka Jernvall, Yilun Yu, Bian Wang, Congyu Yu, Bin Bai, Qian Li, Zifan Zhu, Lun Hai & Yuanqing Wang (2025)
Unravelling eutherian and metatherian divergence through dental evolution
Proceedings of the Royal Society B: Biological Sciences 292 (2061): 20251934
doi: https://doi.org/10.1098/rspb.2025.1934
https://royalsocietypublishing.org/rspb/article-abstract/292/2060/20251934/364709/Unravelling-eutherian-and-metatherian-divergence
The emergence of therian mammals stands as one of the most significant transitions in vertebrate evolution, marked by profound evolutionary innovations, notably the development of tribosphenic molar structures in the conserved dental formulae of postcanines in eutherians (placentals and kin) and metatherians (marsupials and kin). However, elucidating evolutionary paths of these dental transformations has posed enduring challenges. Here, we report detailed morphology of the early eutherian Acristatherium and reconstruct ancestral dental formulae at key nodes of Theria, Eutheria and Metatheria. Our results reveal a distinction among three dental formulae at key nodes of Eutheria, Metatheria and Theria. Contrary to the prevalent hypothesis of serial homology in postcanines, we refine the premolar–molar independence model, initially proposed by Dashzeveg and Kielan-Jaworowska, and emphasize independent development in premolar and molar classes to interpret dental transformations in early therians, based on a synthesis of palaeontological and developmental criteria. It reveals that eutherians lost the distal molar, while metatherians underwent premolar loss when diverging from the therian common ancestor characterized by five premolars and four molars. The pattern of dental transformations suggests distinct evolutionary experimentation over deep time and conserved genetic and developmental controlling mechanisms, ultimately shaping phenotypic diversity.
Unravelling eutherian and metatherian divergence through dental evolution
Proceedings of the Royal Society B: Biological Sciences 292 (2061): 20251934
doi: https://doi.org/10.1098/rspb.2025.1934
https://royalsocietypublishing.org/rspb/article-abstract/292/2060/20251934/364709/Unravelling-eutherian-and-metatherian-divergence
The emergence of therian mammals stands as one of the most significant transitions in vertebrate evolution, marked by profound evolutionary innovations, notably the development of tribosphenic molar structures in the conserved dental formulae of postcanines in eutherians (placentals and kin) and metatherians (marsupials and kin). However, elucidating evolutionary paths of these dental transformations has posed enduring challenges. Here, we report detailed morphology of the early eutherian Acristatherium and reconstruct ancestral dental formulae at key nodes of Theria, Eutheria and Metatheria. Our results reveal a distinction among three dental formulae at key nodes of Eutheria, Metatheria and Theria. Contrary to the prevalent hypothesis of serial homology in postcanines, we refine the premolar–molar independence model, initially proposed by Dashzeveg and Kielan-Jaworowska, and emphasize independent development in premolar and molar classes to interpret dental transformations in early therians, based on a synthesis of palaeontological and developmental criteria. It reveals that eutherians lost the distal molar, while metatherians underwent premolar loss when diverging from the therian common ancestor characterized by five premolars and four molars. The pattern of dental transformations suggests distinct evolutionary experimentation over deep time and conserved genetic and developmental controlling mechanisms, ultimately shaping phenotypic diversity.
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Full text but no free pdf for now:
Z Jack Tseng, Qian Li & Suyin Ting (2025)
Brawn before bite in endemic Asian mammals after the end-Cretaceous extinction
eLife (Reviewed Preprint v1 Dec 18, 2025)
doi: https://doi.org/10.7554/eLife.108917.1
https://elifesciences.org/reviewed-preprints/108917
Z Jack Tseng, Qian Li & Suyin Ting (2025)
Brawn before bite in endemic Asian mammals after the end-Cretaceous extinction
eLife (Reviewed Preprint v1 Dec 18, 2025)
doi: https://doi.org/10.7554/eLife.108917.1
https://elifesciences.org/reviewed-preprints/108917
eLife Assessment
This important study fills a major geographic and temporal gap in understanding Paleocene mammal evolution in Asia and proposes an intriguing "brawn before bite" hypothesis grounded in diverse analytical approaches. However, the findings are incomplete because limitations in sampling design - such as the use of worn or damaged teeth, the pooling of different tooth positions, and the lack of independence among teeth from the same individuals - introduce uncertainties that weaken support for the reported disparity patterns. The taxonomic focus on predominantly herbivorous clades also narrows the ecological scope of the results. Clarifying methodological choices, expanding the ecological context, and tempering evolutionary interpretations would substantially strengthen the study.
Abstract
The first 10 million years (Myr) following the Cretaceous-Paleogene (K-Pg) mass extinction marked a period of global greenhouse conditions and dramatic rise of placental mammals. Because ∼80% of known terrestrial sections capturing post-K-Pg mammal recovery come from North America, a substantial knowledge gap exists in the tempo and mode of recovery in Asia, where only 3% of sites are located and most contain species found nowhere else. We show that isolated Paleocene placental assemblages from China (1) reached high tooth size disparity early in the Paleocene, (2) tracked regional and global environmental changes in their dental shape later in the Paleocene, and (3) achieved maximum dental shape-performance integration near the end of the first 10 Myr post-K-Pg. This ‘brawn before bite’ transformation, coupled with prolonged dental shape versus performance variability, favors a scenario whereby many living orders of placental mammals were borne out of phenotypically and functionally plastic ancestral assemblages, including those in tropical south China, during the Paleocene.
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