The bird manus ‘frameshift’ hypothesis returns in 2021

de Bakker et al. 2021 write:
“The influential ‘frameshift’ hypothesis postulates an evolutionary change in the phenotype of one or more digits in the lineage leading to birds (Wagner and Gauthier 1999; Stewart, et al. 2019). The hypothesis aimed to reconcile conflicting data from developmental biology (Welten, et al. 2005; Richardson 2012; de Bakker, et al. 2013) and palaeontology (Wagner and Gauthier 1999) about the homologies of the wing digits. Developmental data suggest an evolutionary loss of digits I and V from the ancestral pentadactyl forelimb (Kundrát, et al. 2002). For example, putative pre‐cartilage domains for these digits are seen transiently in the chicken and ostrich embryo wing bud (Kundrát, et al. 2002; Welten, et al. 2005; de Bakker, et al. 2013).”

Figure 1. Tawa is the baslmost theropod in the LRT. Like its predecessors, this taxon has a tiny digit 4 and a smaller digit 5. These taxa give rise ultimately to birds with three digits, 1, 2 and 3 without a phase-shift or frame-shift as discussed by de Bakker et al. 2021.

de Bakker et al. 2021 write:
“Palaeontological data, by contrast, point to a pattern of reduction and loss affecting digits IV and V in archosaurs, the clade which includes birds.”

Readers, students, professors,
I encourage you to follow the fossils, not the genes or transient embryo details, which too often deliver false positives. As an example: Bakker et al. nest ducks with chickens and nest swifts with hummingbirds in their figure 8 based on genes. The LRT does not recover those results using traits.

When genetic and embryo results start matching adult trait results,
then we can start listening to gene and embryo studies. In June 2021, gene studies = alchemy. Bogus results occur far too often using gene studies. They only confuse, distract and misdirect. They waste the time of tuition-paying students. Genes never shed light on deep time studies. Embryos also confuse, distract and misdirect while wasting the time and money of students.

,Use traits to learn how every taxon came to be.
You can do this alone, for free if you have Internet access.

References
de Bakker MAG et al. (15 co-authors) 2021. Selection on phalanx development in the evolution of the bird wing. Molecular Biology and Evolution, msab150 doi: https://doi.org/10.1093/molbev/msab150

https://academic.oup.com/mbe/advance-article/doi/10.1093/molbev/msab150/6308563

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