Journal Article10.1017/S009483730001280X
Morphological disparity in Ordovician-Devonian crinoids and the early saturation of morphological space
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TL;DR: Comparison with generic richness reveals that the full range of form was essentially attained by the early part of the Caradocian, long before the time of maximal taxonomic diversity.
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Abstract: It has been argued that many clades originating in the early Paleozoic filled their design space rapidly while still at low taxonomic diversity. Standardization of morphology for analytical purposes facilitates testing of this claim. Here I document evolutionary patterns of morphological disparity in Ordovician-Devonian crinoids, using a set of 75 discrete characters covering the principal features of the crinoid stem, cup, tegmen, and arms. Disparity is measured as the average dissimilarity among species, the range of morphospace occupied, and the number of realized character-state combinations. Comparison with generic richness reveals that the full range of form was essentially attained by the early part of the Caradocian, long before the time of maximal taxonomic diversity. Despite subsequent taxonomic diversification, the variety of crinoid form did not expand appreciably; increased diversity was accommodated by the evolution of variations upon the spectrum of designs established earlier. The data discussed here do not definitively imply specific sources of constraint, but the effective stasis in disparity supports previous arguments that some morphological limits were reached early in crinoid history.
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Citations
Early bursts of body size and shape evolution are rare in comparative data.
Luke J. Harmon,Luke J. Harmon,Jonathan B. Losos,T. Jonathan Davies,Rosemary G. Gillespie,John L. Gittleman,W. Bryan Jennings,Kenneth H. Kozak,Mark A. McPeek,Franck Moreno-Roark,Thomas J. Near,Andy Purvis,Robert E. Ricklefs,Dolph Schluter,James A. Schulte,Ole Seehausen,Ole Seehausen,Brian L. Sidlauskas,Brian L. Sidlauskas,Omar Torres-Carvajal,Jason T. Weir,Arne Ø. Mooers +21 more
TL;DR: It is suggested that the classical model of adaptive radiation, where morphological evolution is initially rapid and slows through time, may be rare in comparative data.
Testing for different rates of continuous trait evolution using likelihood
TL;DR: General predictions regarding changes in phenotypic diversity as a function of evolutionary history and rates are developed, and tests are derived to evaluate rate changes, showing that these tests are more powerful than existing tests using standardized contrasts.
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Rates of speciation and morphological evolution are correlated across the largest vertebrate radiation
Daniel L. Rabosky,Francesco Santini,Jonathan M. Eastman,Stephen A. Smith,Brian L. Sidlauskas,Jonathan Chang,Michael E. Alfaro +6 more
TL;DR: It is demonstrated that rates of species diversification are highly correlated with the rate of body size evolution across the 30,000+ living species of ray-finned fishes that comprise the majority of vertebrate biological diversity.
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The evolution of morphological diversity
TL;DR: Quantitative morphological studies reveal profound changes in evolutionary rates corresponding with the generation of morphological disparity at low taxonomic diversity during the early radiation of many clades.
Ecological opportunity and the rate of morphological evolution in the diversification of Greater Antillean anoles.
TL;DR: The results provide a complementary perspective, indicating that the rate of phenotypic diversification declines with decreasing opportunity in an adaptive radiation.
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