Phylogeny is not taxonomy: lessons on higher classification from turtle and whale barnacles (Cirripedia: Coronuloidea)

Hayashi, R.; Collareta, A.

2026-09-12 zoology

10.64898/2026.09.05.749650 bioRxiv

Show abstract

Phylogeny and taxonomy are related but not identical: phylogeny estimates common ancestry, whereas taxonomy must also provide diagnosable, stable, informative, and useful classifications. We examine this distinction using turtle and whale barnacles of the superfamily Coronuloidea, a group with an extensive fossil record, marked ecological specialization, a long history of morphology-based classification, and a recent topology-driven reclassification that merged recognized higher taxa to preserve monophyly. These changes reduced diagnosability and biological coherence, weakened historical continuity, and relied on placements insufficiently tested against morphological and phylogenetic evidence. Our reanalysis of published molecular datasets shows that critical relationships are sensitive to marker composition and taxon sampling. Together with morphological considerations on extant and fossil forms, these results indicate that topology alone is insufficient for coherent higher classification. We argue that higher taxa should be evaluated using complementary criteria: diagnosability, stability, utility, and monophyly, rather than by mechanically translating a preferred tree into Linnaean ranks.

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