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Examples of fossil trait sequences that are best fit by each of the three evolutionary models. (A) Directional evolution: shell shape in the planktonic foraminifera Contusotruncana from DSDP site 384 (45). (B) Unbiased random walk: shell width in the land snail Mandarina (46). (C) Stasis: shell shape (convexity) in the bivalve Chesapecten nefrens (34).
