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Titolo:
Exhaustion of morphologic character states among fossil taxa
Autore:
Wagner, PJ;
Indirizzi:
Field Museum Nat Hist, Dept Geol, Chicago, IL 60605 USA Field Museum Nat Hist Chicago IL USA 60605 pt Geol, Chicago, IL 60605 USA
Titolo Testata:
EVOLUTION
fascicolo: 2, volume: 54, anno: 2000,
pagine: 365 - 386
SICI:
0014-3820(200004)54:2<365:EOMCSA>2.0.ZU;2-P
Fonte:
ISI
Lingua:
ENG
Soggetto:
GROUP CALMONIIDAE TRILOBITA; CLADISTIC-ANALYSIS; PHYLOGENETIC-RELATIONSHIPS; CONFIDENCE-INTERVALS; EVOLUTIONARY TRENDS; STRATIGRAPHIC RANGES; LIKELIHOOD APPROACH; AMNIOTE PHYLOGENY; SYSTEMATICS; COMPATIBILITY;
Keywords:
character spaces; constraints; exhaustion; fossils; homoplasy; phylogeny; saturation;
Tipo documento:
Review
Natura:
Periodico
Settore Disciplinare:
Agriculture,Biology & Environmental Sciences
Life Sciences
Citazioni:
139
Recensione:
Indirizzi per estratti:
Indirizzo: Wagner, PJ Field Museum Nat Hist, Dept Geol, Roosevelt Rd & Lake Shore Dr,Chicago, IL 60605 USA Field Museum Nat Hist Roosevelt Rd & Lake Shore Dr Chicago IL USA 60605
Citazione:
P.J. Wagner, "Exhaustion of morphologic character states among fossil taxa", EVOLUTION, 54(2), 2000, pp. 365-386

Abstract

Frequencies of new character state derivations are analyzed for 56 fossil taxa. The hypothesis that new character states are added continuously throughout clade history can be rejected for 48 of theses clades. Two alternative explanations are considered: finite states and ordered states. The formerhypothesizes a limited number of states available to each character and istested using rarefaction equations. The latter hypothesizes that there arelimited possible descendant morphologies for any state, even if the character has infinite potential states. This is tested using power functions. The finite states hypothesis explains states:steps relationships significantly better than does the ordered states hypothesis in 14 cases; the converse is true for 14 other cases. Under either hypothesis, trilobite clades show appreciably more homoplasy after the same numbers of steps than do molluscs, echinoderms, or vertebrates. The prevalence of the exhaustion pattern among different taxonomic groups implies that worker biases are not to blame and instead implicates biological explanations such as intrinsic constraints or persistent selective trends. Regardless of the source of increased homoplasy, clades appear to exhaust their available character spaces. Nearly all examined taxa show significant increases in proportions of incompatible character pairs (i.e., those necessarily implying homoplasy) as progressively younger taxa are added to character matrices. Thus, a deterioration of hierarchical structure accompanies character state exhaustion. Exhaustion has several implications: (1) thebasic premise of cladistic analyses (i.e., that maximum congruence reflects homology rather than homoplasy) becomes increasingly less sound as cladesage; (2) sampling high proportions of taxa probably is needed for congruence to discern homoplasy from homology; (3) stratigraphic data might be necessary to discern congruent homoplasy from congruent homology; and (4) in many cases, character states appear to have evolved in ordered patterns.

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Documento generato il 22/09/20 alle ore 16:27:35