|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 Gene Hunt. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013-7012. hunte{at}si.edu
For almost 30 years, paleontologists have analyzed evolutionary sequences in terms of simple null models, most commonly random walks. Despite this long history, there has been little discussion of how model parameters may be estimated from real paleontological data. In this paper, I outline a likelihood-based framework for fitting and comparing models of phyletic evolution. Because of its usefulness and historical importance, I focus on a general form of the random walk model. The long-term dynamics of this model depend on just two parameters: the mean (µstep) and variance (
2step) of the distribution of evolutionary transitions (or "steps"). The value of µstep determines the directionality of a sequence, and 2step governs its volatility. Simulations show that these two parameters can be inferred reliably from paleontological data regardless of how completely the evolving lineage is sampled.
In addition to random walk models, suitable modification of the likelihood function permits consideration of a wide range of alternative evolutionary models. Candidate evolutionary models may be compared on equal footing using information statistics such as the Akaike Information Criterion (AIC). Two extensions to this method are developed: modeling stasis as an evolutionary mode, and assessing the homogeneity of dynamics across multiple evolutionary sequences. Within this framework, I reanalyze two well-known published data sets: tooth measurements from the Eocene mammal Cantius, and shell shape in the planktonic foraminifera Contusotruncana. These analyses support previous interpretations about evolutionary mode in size and shape variables in Cantius, and confirm the significantly directional nature of shell shape evolution in Contusotruncana. In addition, this model-fitting approach leads to a further insight about the geographic structure of evolutionary change in this foraminiferan lineage.
This article has been cited by other articles:
|
|
 |
|
  C. Simpson and P. G. Harnik Assessing the role of abundance in marine bivalve extinction over the post-Paleozoic Paleobiology, December 1, 2009; 35(4): 631 - 647. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Jones Directional evolution in the conodont Pterospathodus Paleobiology, September 1, 2009; 35(3): 413 - 431. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. H.G. Ezard and A. Purvis paleoPhylo: free software to draw paleobiological phylogenies Paleobiology, September 1, 2009; 35(3): 460 - 464. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. F. Pachut and R. L. Anstey Inferring evolutionary modes in a fossil lineage (Bryozoa: Peronopora) from the Middle and Late Ordovician Paleobiology, March 1, 2009; 35(2): 209 - 230. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. C. Wang and A. M. Bush Adjusting global extinction rates to account for taxonomic susceptibility Paleobiology, December 1, 2008; 34(4): 434 - 455. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Grey, J. W. Haggart, and P. L. Smith Variation in Evolutionary Patterns Across the Geographic Range of a Fossil Bivalve Science, November 21, 2008; 322(5905): 1238 - 1241. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Hunt Gradual or pulsed evolution: when should punctuational explanations be preferred? Paleobiology, September 1, 2008; 34(3): 360 - 377. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Alizon, M. Kucera, and V. A. A. Jansen Competition between cryptic species explains variations in rates of lineage evolution PNAS, August 26, 2008; 105(34): 12382 - 12386. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. M. Novack-Gottshall and M. A. Lanier Scale-dependence of Cope's rule in body size evolution of Paleozoic brachiopods PNAS, April 8, 2008; 105(14): 5430 - 5434. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. M. Novack-Gottshall Ecosystem-wide body-size trends in Cambrian-Devonian marine invertebrate lineages Paleobiology, March 1, 2008; 34(2): 210 - 228. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Hunt From the Cover: The relative importance of directional change, random walks, and stasis in the evolution of fossil lineages PNAS, November 20, 2007; 104(47): 18404 - 18408. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
