Avian chronoclassification

Applying a set of exemplary cutoffs to the family-level timetree of Kuhl et al. (2021) results in the following avian chronoclassification: 

Avian chronoclassification (right) derived from the family-level timetree of Kuhl et al. (2021) (left) after applying a series of cutoffs. 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 return to Linnaean classification. The use of two alternative (zoo-)taxonomic systems (ICZN and PhyloCode) should definitely be discontinued.


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. (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)