Reconstructing the archosaur radiation using a Middle Triassic archosauriform tooth assemblage from Tanzania

Area of Science:

• Paleontology
• Evolutionary Biology
• Vertebrate Morphology

Background:

• Archosauriformes, including crocodylians and birds, diversified globally after the Permo-Triassic mass extinction.
• The timing of dietary specialization relative to taxonomic diversification in early Archosauriformes remains unclear.
• Few Early-Middle Triassic tooth assemblages exist, limiting understanding of early archosaur evolution and morphological diversity.

Purpose of the Study:

• To investigate the taxonomic composition and morphological diversity of an Early-Middle Triassic archosauriform tooth assemblage from the Manda Beds, Tanzania.
• To determine if dietary specialization coincided with or followed initial lineage diversification in Archosauriformes.
• To develop a model for differentiating and assigning isolated archosauriform teeth to species or genus.

Main Methods:

• Collected and analyzed a tooth assemblage from the Middle Triassic Manda Beds (2007-2017).
• Created a dataset of quantitative and discrete morphological characters from in situ teeth (N=65) and isolated teeth (N=31).
• Utilized crown heights to predict tooth base ratio, creating a quantitative morphospace; employed non-metric multidimensional scaling with 11 binary characters.

Main Results:

• The majority of isolated Manda Beds teeth fall within the morphospace of *Nundasuchus* and *Parringtonia*, indicating a plesiomorphic archosauriform tooth condition.
• Two isolated teeth were exclusively assigned to a *Pallisteria* morphospace.
• A significant overlap in tooth morphology among species suggests that dietary specialization lagged behind species diversification in these Middle Triassic archosauriforms.

Conclusions:

• The study demonstrates that conservative tooth morphologies in Archosauriformes can be differentiated and assigned, making the model useful for identifying isolated teeth.
• Dietary specialization in Archosauriformes from the Manda Beds evolved after species diversification, supporting Simpson's "adaptive zones" model.
• The methods used are transferable for reconstructing ecological radiations in other vertebrate taxa throughout Earth's history.