Hunt, Gene (2007): The relative importance of directional change, random walks, and stasis in the evolution of fossil lineages

DSDP 43 384


Hunt, Gene
Smithsonian Institution, National Museum of Natural History, Department of Paleobiology, Washington, DC, United States

The relative importance of directional change, random walks, and stasis in the evolution of fossil lineages
Proceedings of the National Academy of Sciences of the United States of America
National Academy of Sciences, Washington, DC, United States
The nature of evolutionary changes recorded by the fossil record has long been controversial, with particular disagreement concerning the relative frequency of gradual change versus stasis within lineages. Here, I present a large-scale, statistical survey of evolutionary mode in fossil lineages. Over 250 sequences of evolving traits were fit by using maximum likelihood to three evolutionary models: directional change, random walk, and stasis. Evolution in these traits was rarely directional; in only 5% of fossil sequences was directional evolution the most strongly supported of the three modes of change. The remaining 95% of sequences were divided nearly equally between random walks and stasis. Variables related to body size were significantly less likely than shape traits to experience stasis. This finding is in accord with previous suggestions that size may be more evolutionarily labile than shape and is consistent with some but not all of the mechanisms proposed to explain evolutionary stasis. In general, similar evolutionary patterns are observed across other variables, such as clade membership and temporal resolution, but there is some evidence that directional change in planktonic organisms is more frequent than in benthic organisms. The rarity with which directional evolution was observed in this study corroborates a key claim of punctuated equilibria and suggests that truly directional evolution is infrequent or, perhaps more importantly, of short enough duration so as to rarely register in paleontological sampling.
Coverage:Geographic coordinates:
West:-51.3948East: -51.3948

Invertebrate paleontology; Actinopterygii; Akaike information criterion; Arthropoda; Atlantic Ocean; benthic taxa; biologic evolution; Bivalvia; Chesapecten; Chordata; Conodonta; Contusotruncana; Crustacea; Deep Sea Drilling Project; directional change; directional evolution; DSDP Site 384; Foraminifera; fossil record; Gastropoda; gradualism; Invertebrata; Leg 43; Mammalia; Mandarina; Mandibulata; maximum likelihood; microfossils; Mollusca; North Atlantic; Osteichthyes; Ostracoda; Pectinacea; Pectinidae; Pisces; Protista; Pteriina; Pterioida; quantitative analysis; Radiolaria; random walks; shape analysis; shells; stasis; statistical analysis; stochastic processes; Teleostei; Tetrapoda; Trilobita; Trilobitomorpha; Vertebrata;