Mesozoic birds show independent random tooth loss in evolution of tooth number and size (free pdf)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

Free pdf:

Yachun Zhou, Yan Zhao, Ying Guo, Xinsen Wei & Fucheng Zhang (2026)
Evolution of tooth number and size reveals random evolution and weak directional selection of dentition toward independent tooth loss in Mesozoic birds
Avian Research 100397
doi: https://doi.org/10.1016/j.avrs.2026.100397
https://www.sciencedirect.com/science/article/pii/S2053716626000605


How their toothed jaws evolve to edentulous beaks remains a key puzzle in the early birds. Although some studies using discrete data of dentition have rejected the hypotheses of long-term directional selection or weight-saving adaptations, a more detailed evolutionary pattern of dentition reduction is poorly quantified. Here for the first time, we analyze four essential parameters including tooth number on premaxilla, maxilla, and dentary, and average tooth crown size across a phylogeny of 21 key genera in Mesozoic birds. Our phylogenetic comparative analyses reveal that the evolution of tooth number is best described by the Brownian motion (BM) model, and this evolution is a random process driven primarily by time and phylogeny, with no evidence for a global trend towards tooth loss. However, at the same time, the evolution of tooth crown size shows a weak but detectable signal of directional selection (Ornstein-Uhlenbeck model) towards a smaller teeth and independent of body size, which may reflect an evolutionary transition of jaw function or feeding behavior. Furthermore, we quantify that the complete tooth loss occurred independently in at least four lineages (e.g., Confuciusornis, Gobipteryx, Archaeorhynchus, Schizooura), and the key ancestral nodes are not edentulous. Lastly, we conclude that the predominant mode of dentition evolution in Mesozoic birds is random. The localized and independent events of tooth loss are likely driven by the lineage-specific ecological or developmental factors. Furthermore, the origin of modern bird-like digestive system, rather than the strong selective pressure, should be the key biological trigger to the tooth loss.

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[Mickey Mortimer]

This is yet another example of attempting analysis based on a very questionable primary dataset. "The tooth number and crown size are sampled from the 31 well-preserved 116 specimens of the 21 critical genera of Mesozoic birds." 21 Mesozoic birds with skulls? Is this the year 2002?

Issue #1 is reliance on a topology that's not consensus because there is barely any consensus on topology within Enantiornithes, in non-Aves Euornithes or among the three classic basal avialans (Sapeornis, Jeholornis, Confuciusornis). So yeah, Gobipteryx sister to bohaiornithids, Eoenantiornis sister to that and a Cathayornis plus longipterygid clade sister to that? Just one idea. Bohaiornithids being monophyletic themselves (with that content) is itself disputed. I can't even recall a paper with confuciusornithids sister to omnivoropterygids like this paper's phylogram. 

Issue #2 is taxon exclusion. No toothless Zhongjianornis or toothed jinguofortisids? You think instead of having Gobipteryx as the only Late Cretaceous and the only toothless enentiornithine, having Gobipipus, Imparavis, Navaornis and Yuornis might affect results? And in Euornithes, no Meemannavis or Xinghaiornis among toothless taxa, or Iteravis, Gansus, Juehuaornis/Changzuiornis/Dingavis, Shuilingornis, Hongshanornis or Khinganornis among toothed taxa?

"we quantify that the complete tooth loss occurred independently in at least four lineages (e.g., Confuciusornis, Gobipteryx, Archaeorhynchus, Schizooura), and the key ancestral nodes are not edentulous." I would say DUH, but I don't think this paper quantified Archaeorhynchus not being a schizoourid at all, and just assumed that based on whatever topology they accepted as correct. 

Look, as much as everyone might want higher level analyses, they are worthless until topologies are accepted as consensus. And that requires more and better primary analyses.

Mickey Mortimer