The content discusses the discovery of new Jurassic shuotheriid fossils and their implications for understanding the evolution of mammaliaform dentition. Key points:
Shuotheriids are Jurassic mammaliaforms with pseudotribosphenic teeth, where the pseudotalonid is anterior to the trigonid, unlike the tribosphenic pattern of therian mammals.
The new shuotheriid specimens allow reidentification of dental structures using serial homology and tooth occlusal relationships, contrary to the conventional view.
Phylogenetic analysis based on the new evidence removes shuotheriids from the tribosphenic ausktribosphenids and clusters them with docodontans, forming a new clade called Docodontiformes characterized by pseudotribosphenic features.
The phylogeny suggests that docodontiforms and 'holotherians' (Kuehneotherium, monotremes, and therians) evolved independently from a Morganucodon-like ancestor with triconodont molars.
The pseudotribosphenic pattern passed through a cusp semitriangulation stage, while the tribosphenic pattern and its precursor went through a cusp triangulation stage, resulting in the earliest diversification of mammaliaform dental structures.
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by Fangyuan Mao... at www.nature.com 04-03-2024
https://www.nature.com/articles/s41586-024-07258-7Deeper Inquiries