Note: "CLASSification"

In the following, the temporally-banded avian timetree of Kuhl et al., 2021 (see Note "Temporal banding") is transcribed into a CLASSification by pooling clades into categories of age-defined ranks. A few new names, represented in quotation marks, had to be introduced for clades ranked as infraclasses and superorders. 


For the transcription of the avian timetree into a rank-based CLASSification, I had to refer to ages of total clades, because ages of crown clades haven´t been determined for most orders and families by Kuhl et al. (2021). In principle, however, it would also be possible to consider crown-clade ages. 

Overall, the results show a high level of agreement between the traditional and the new classification. Passeriformes, however, are a notable exception to this rule. While more than one hundred families are traditionally recognised in this order, the present CLASSification accepts 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, and most authorsdo not favour a strictly age-based classification. While the usefulness of the approach as an accessory classification tool is generally acknowledges, most taxonomists seem to fear that easily diagnosable and long-established clades of their primary research area might be split or lumped. While I consider most of their arguments unconvincing, it is definitely true that the precise reconstruction of divergence times is still very demanding.  

However, even critics of the temporal-banding approach concur that temporal outliers (like Mirandornithes and Passeriformes) should be adjusted to better fit into the classification of the clade as a whole. 




Even critics of the approach concur that temporal outliers (like Mesitornithes and Passeriformes in Aves) should be adjusted to better conform to their respective clades. Last but not least, implementation of temporal banding might convince proponents of the PhyloCode to accept the Linnaean classification in its modified form.   


The new CLASSification prompts the question how to integrate the fossil record of extinct clades into the age-based classification system. An elegant solution has been proposed by Lücking (2019), who suggests the application of relative temporal bands considering the lifespan of lineages, irrespective of the absolute time at which they populated planet Earth. 


CLASSification of extant Aves based on the timetree of Kuhl et al. (2021), to which temporal banding has been applied (see Note: "Temporal banding"). The ranking of clades is defined by a series of cut-off timelines that are separated from each other by equidistant intervals of 10 myr. Lower ranks (tribes and genera) are not yet considered. The numbers of clades assigned to each rank are given in parentheses.