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The stability of thoracic segmentation in trilobites: a case study in developmental and ecological constraints
Author(s) -
Hughes Nigel C.,
Chapman Ralph E.,
Adrain Jonathan M.
Publication year - 1999
Publication title -
evolution and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.651
H-Index - 78
eISSN - 1525-142X
pISSN - 1520-541X
DOI - 10.1046/j.1525-142x.1999.99005.x
Subject(s) - trilobite , biology , body plan , clade , taxon , arthropod , paleontology , evolutionary biology , ecology , zoology , phylogenetics , embryo , biochemistry , ordovician , gene , microbiology and biotechnology
The decline in origination rate of new metazoan body plans following the Cambrian radiation has been suggested to reflect developmental canalization in derived taxa, limiting their ability to evolve forms with radically different morphotypes. Segmentation is a fundamental aspect of arthropod body plan, and here we show that a derived trilobite that secondarily converged on a morphotype characteristic of basal members of the clade also reverted to a pattern of segmental variability common among basal trilobites. Hence a secular trend in loss of variability of the trilobite thorax was not due to the evolution of an inviolable developmental constraint. This result challenges the notion of developmental canalization in phylogenetically derived taxa. Rather, early variability in trilobites may be the result of ecological factors that promoted segment‐rich thoracic morphotypes during Cambrian time.