Applying a set of exemplary cutoffs to the family-level timetree of Kuhl et al. (2021) results in the following avian chronoclassification:
Exemplary avian chronoclassification (right) derived from the family-level timetree of Kuhl et al. (2021) (left) after applying a series of cutoffs (indicated by broken lines at 15, 25, 35, 45, 55, 65,75, and 85 Ma). Higher-level taxa for which no clade names are available are indicated as not named (n.n.).
Overall, the resulting avian chronoclassification shows a high degree of compliance with traditional classifications. Passeriformes, however, are a notable exception. While more
than one hundred families are traditionally recognised in this order, the proposed chronoclassification recognises just seven families, which still is the highest number of any avian
order.
The pros and cons of temporal banding have been extensively discussed elsewhere (e.g. Kraichach et al., 2017; Lücking, 2019). Most authors have expressed concerns against
strictly age-based classification. While the usefulness of the approach as an accessory tool is acknowledged (e.g. for obvious temporal outliers like Mirandornithes and Passeriformes), most
taxonomists don‘t want diagnosable and long-established monophyletic clades to be split or lumped. While I consider most of their arguments not particularly convincing, it is certainly true that
the reconstruction of divergence times is still a major scientific challenge that needs to be addressed.
Implementation of strict chronotaxonomics might also pave the way for proponents of the PhyloCode (rejecting categorical ranks) to accept Linnaean classification. The use of two
alternative zootaxonomic systems (ICZN and PhyloCode) should be discontinued.
References
Kraichak E, Crespo A, Divakar PK, Leavitt SD, and Lumbsch HT (2017), A temporal banding approach for consistent taxonomic ranking above the species level, Sci. Rep. 7, e:2297. (pdf)
Kuhl H, Frankl-Vilches C, Bakker A, Mayr G, Nikolaus G, Boerno ST, Klages S, Timmermann B, and Gahr M (2021), An unbiased molecular approach using 3'UTRs resolves the avian family-level tree of life, Mol. Biol. Evol. 38, 108-127. (free pdf)
Lücking R (2019), Stop the abuse of time! Strict temporal banding is not the future of rank-based classifications in fungi (including lichens) and other organisms, CRC Crit. Rev. Plant Sci. 38, 199-253. (abstract)