When morphology meets molecular data in crinoid phylogeny: A challenge
Résumé
The extant crinoid fauna results from more than 485 Myr of evolution (from Early Ordovician). Detailed morphological studies on extant crinoids document large intraspecific variations, strong changes through ontogeny with various mosaics of heterochronic development, and adaptive characters which depend on environment, mainly hydro - dynamics and food supply. The importance of paedomorphy and morphological convergences (homoplasies) in crinoid evolution is confirmed by studies using DNA markers, and makes difficult the use of cladistic methods of phylogenetic reconstructions. Many clades of extant crinoids based on external skeleton morphology are polyphyletic. Using the hyocrinids and a recent extensive molecular phylogeny of the extant crinoids, we show that the molecular approach, when coupled with detailed ontogenetic analyses on a large sample of specimens and taxa, may help understand the evolutionnary trends within a given group of organisms. Purely molecular or phenotypic analyses produce contrasting results because these analyses work at scales that are separated by a strong gap. We propose a deep reappraisal of the relationships between extant and fossil taxa using the concept of ontophylogeny which rejects the classical separation between ontogeny and phylogeny and argues that natural selection acts at every level of integration of the organism from DNA, cells, tissues, to the individuals and populations.