Note "Temporal banding”

In traditional classifications, the age of clades is not taken into account. However, modern techniques now allow divergence times to be assessed with sufficient accuracy, although they may still differ widely among authors. 

Divergence-time estimates are based on molecular dating techniques, which in turn depend on reliable fossil calibrations, i. e. correctly dated and placed fossils. To some extent they also depend on the selection of fossils and the maximum age constraint set by investigators.

Time-calibrated ( dated) phylogenies, in which branch lengths are proportional to time, are usually referred to as chronograms or less often as timetrees. I prefer the latter term because of its euphony. 

Dated phylogenies allow clades to be ranked according to their geological ages. Clades recognised at the same rank are then of comparable age. To establish age-based classifications, cut-off timelines (also called cut-off ages, limits, lines, or points) have to be defined for each categorical rank. This approach, first recognised by Willi Hennig (1966), has been termed „temporal banding“ by Avise & Johns (1999). The term refers to the time period between consecutive cut-off timelines. 

The ultimate challenge for applying the temporal banding approach to timetrees will be answering the question to which groups of organisms the same temporal cut-off timelines shall be applied. Here, I will apply the approach to the clade Aves that has been ranked as a „class“ since Linnaeus (1758), thus literally providing a CLASSification. In Wikipedia (as of Max 2021), a list of 107 animal classes is given, e.g. Amphibia, Aves, Gastropoda, Insecta, and Mammalia. 

To provide temporal information to clades above class- level, either so-called timeclips (Avise & Mitchell, 2007), or just age information could be used (Zachos, 2011). The dual approach would combine nomenclatural stability within individual classes, and comparability among different classes. 

In the following, the approach of temporal banding is applied to the avian timetree of Kuhl et al. (3021). To provide the basis for assigning a categorical rank to each clade, a continuous series of cut-off timelines has been defined: 

The choice of cut-off timelineswas initially determined by setting the age of avian orders at 55 mya. The remaining cut-off timelines were then aligned at 10 myr intervals for higher, and at 2,5 myr intervals for lower categorical ranks in order to roughly conform to the results of Holt & Jønsson (2014). In their pioneering study the authors cut phylogenies at ages that returned the same number of clades as found in the originalrankings, resulting in cut-off timelines of 65 mya for orders, 37 mya for families, and 11 myr ago for genera. 

It is stressed that cut-off tinelines are fully arbitrary (though of course not haphazardly) and only depend on the consensus of taxonomists.

Holt & Jønsson (2014), who based their study on the timetree of Jetz et al. (2012), also demonstrated that the intrinsic classification of Passeriformes is not compatible with the other avian orders. For example, they lumped 14 out of 15 families of Passeroidea into a single family. 

To preserve traditional passeriform families, Jonsson et al. (2016) in their study on Corvides had to assign family rank to clades at onl 21.5 mya. In another study on Passeriformes, Cai et al. (2019) assignes family status at only 18 mya. However, these very young family ages to not comply with avian classification in general. 

Futuristic family-level timetree of extant Aves based on Kuhl et al. (2021), to which temporal banding has been applied here. A number of clades that are traditionally considered families will have to be downgraded to subfamily or tribal rank, or even below (red, orange and yellow family names, respectively). In Passeriformes, however, the situation is quite challenging, as more than one hundred traditional families will have to be merged to only seven families. On the other hand, some traditional families will have to be split, e.g. Cuculidae and Scolopacidae. 

 

Futuristic order-level timetree of extant Aves based on Kuhl et al. (2021), to which temporal banding has been applied here. The cut-off timelines at 55 myr and 65 myr  were chosen to define oders and superorders, respectively. As a result, several traditional orders had to be split (blue and green order names), while only two traditional orders, flamingos (Phoenicopteriformes) and grebes (Podicipediformes), had to be merged (red order name). It would have been possible to set the superordinal cut-off timeline at 65,5 myr to retain loons (Gaviiformes) in traditional Aequornithes. However, I found it tempting to set cut-off timelines in steps of 10 myr. The new taxonomy distinguishes 43 orders and 10 superorders. Note that crown-group ages derived from Kuhl et al. (2021, suppl.) are indicated by blue lines, whereas crown-group ages derived from other sources are indicated by green lines. 

References/Literature

Avise JC, and Johns GC (1999), Proposal for a standardized temporal scheme of biological classification for extant species, Proc. Natl. Acad. Sci. USA 96, 7358-63. (pdf)


Avise JC, and Mitchell D (2007), Time to standardize taxonomies, Syst. Biol. 56, 130-133. (pdf)


Avise JC, and Liu JX (2011), On the temporal inconsistencies of Linnean taxonomic ranks, Biol. J. Linn. Soc. 102, 707-714. (pdf)


Cai T, Cibois A, Alström P, Moyle RG, Kennedy JD, Shao S, Zhang R, Irestedt M, Ericson PGP, Gelang M, Qu Y, Lei F, and Fjeldså (2019), Near-complete phylogeny and taxonomic revision of the world’s babblers (Aves: Passeriformes), Mol. Phylogenet. Evol. 130, 346-356. (open manuscript)


Divakar PK, Crespo A, Kraichak E, Leavitt SD, Singh G, Schmitt I, and Lumbsch HT (2017), Using a temporal phylogenetic method to harmonize family- and genus-level classification in the largest clade of lichen-forming fungi, Fungal Divers. 84, 101-117. (abstract)

 

Dubois A (2008), Phylogenetic hypotheses, taxa and nomina in zoology, Zootaxa 1950, 51-86. (pdf)

 

Härlin M (2005), Definitions and phylogenetic nomenclature, ProcCalifAcadSci. 56Suppl. 1 (19), 216-224.   

 

Hennig W (1966) Phylogenetic systematics, University of Illinois Press, Chicago, IL. (link)

 

Holt BG, and Jønsson KA (2014), Reconciling hierarchical taxonomy with molecular phylogenies, Syst. Biol. 63, 1010-17(pdf) (suppl.)

 

Jetz W, Thomas GH, Joy JB, Hartmann K, and Mooers AO (2012), The global diversity of birds in space ant time, Nature 491, 444-448. (abstract)

 

Jønsson KA, Fabre PH, Kennedy JD, Holt BG, Borregaard MK, Rahbek C, and Fjeldså J (2016), A supermatrix phylogeny of corvoid passerine birds (Aves: Corvides), Mol. Phylogenet. Evol. 94, 87-94. (abstract) 


Kallal RJ, Dimitrov D, Arnedo M, Giribet G, and Hormiga G (2020), Monophyly, taxon sampling, and the nature of ranks in the classification of orb-weaving spiders (Araneae: Araneoidea), Syst. Biol. 69, 401-411. (abstract)

 

Kraichak E, Crespo A, Divakar PK, Leavitt SD, Lumbsch HT (2017), A temporal banding approach for consistent taxonomic ranking above the species level, Sci. Rep. 7, 2297. (pdf)


Kuntner M, Hamilton CA, Cheng RC, Gregoric M, Lupse N, Lokovsek T, Lemmon EM, Lemmon AR, Agnarsson I, Coddington JA, and Bond JE (2019), Golden orbweavers ignore biological rules: phylogenomic and comparative analyses unravel a complex evolution of sexual size dimorphism, Syst. Biol. 68, 555-572. (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)  


Naomi SI (2014), Proposal of an integrated framework of biological taxonomy: a phylogenetic taxonomy, with the method of using names with standard endings in clade nomenclature, Bionomina 7, 1-44. (pdf)

 

O´Hara TD, Hugall AF, Thuy B, Stöhr S, and Martynov AS (2017) Restructuring higher taxonomy using broad scale phylogenomics: the living Ophiuroidea, Mol. Phylogenet. Evol. 107, 415-430. (abstract)

 

Talavera G, Lukhtanov VA, Pierce NE, and Vila R (2012), Establishing criteria for higher-level classification using molecular data: the systematics of Polyommatus blue butterflies (Lepidoptera, Lycaenidae), Cladistics 29, 166-192. (pdf) 

 

Vences M, Guayasamin JM, Miralles A, and de la Riva I (2013), To name or not to name: criteria to promote economy of change in Linnaean classification schemes, Zootaxa 3636, 201-244. (pdf)


Zachos FE (2011), Linnean ranks, temporal banding, and time-clipping: why not slaughter the sacred cow? Biol. J. Linn. Soc. 103, 732-734. (pdf) 


Zhao RL, Zhou JL, Chen J, Margaritescu S, Sanchéz-Ramírez S, Hyde KD, Callac P, Parra LA, Li GJ, and Moncalvo JM (2016), Towards standardizing taxonomic ranks using divergence times - a case study for reconstruction of the Agaricus taxonomic system, Fungal Divers. 78, 239-292. (abstract)