April, 2000 
SCAMIT Newsletter 
Vol. 18, No. 12 
sedimentation in the ocean were minimal since 
sediment produced by erosion during orogeny 
was at least partially contained on land. During 
periods of plate divergence maxima of turbidity 
and sedimentation was obtained. These 
maximal and minimal periods correlate with a 
number of biological trends, and offer 
explanations for many inadequately explained 
evolutionary events. Marcotte marshals a 
diverse array of information drawn from 
various disciplines in support of his hypothesis. 
A number of points, considering the 
information provided in support, click with a 
“oh, that seems obvious” sort of reaction. 
Whether or not this hypothesis survives the 
challenges that will undoubtedly be brought 
against it, the article is a stimulating one which 
no one interested in the history of life will fail 
to enjoy. 
Giribet & Wheeler (1999), in a reanalysis of 
the dataset used earlier to place arthropods 
among other metazoans (Giribet & Ribera, 
1998), suggest some changes in the previous 
analysis. They use an iterative method called 
“the parsimony rachet” in this effort, a 
sequential optimization strategy that 
significantly reduces the time to locate shorter 
tree lengths. In this paper they confirmed many 
of their previous conclusions and resolved a 
series of polychotomies in the earlier strict 
consensus tree, but it was unclear in the result 
if Tr chozoa represented a clade or a grade. 
Existence of Ecdysozoa, deuterostomes, and 
acoelomate platyhelminth clades within the 
Bilateria were supported by the analysis, but 
the included taxa sample was apparently not 
sufficient to fully resolve the status of the 
Trochozoa. The authors were very satisfied 
with the 18S rDNA gene as a substrate for high 
level analysis of metazoan relationships, but 
felt that it alone would not provide good 
resolution of relationships within the major 
clades. Wagele et al (1999) raise questions 
about the 18S rDNA evidence based on 
subsequent analyses, and are not sure that 
Ecdysozoa is valid, especially since the 
competing Articulata concept is well supported 
on long established morphological bases. 
The differing interpretations of 18S rDNA 
evidence mentioned above highlight the 
continuing methodological debates in cladistic 
analysis. Even more basic are the philosophical 
points discussed by Harlin, 1999 in 
consideration of the logical impropriety of 
emphasis on characters rather than trees in 
phylogenetic taxonomy. 
It has long been assumed that release of 
planktonic larvae results in relatively 
unconstrained dispersal of a population and 
good gene flow between subpopulations 
occupying disjunct habitat. Of late this 
assumption has been tested, sometimes with 
unexpected results. Cowen et al (2000) 
correctly note that the assumed genetic 
exchange is a vital part of studies concerning 
population dynamics of any individual species, 
and an essential basis for fishery management 
and environmental policy decisions. They then 
test the assumptions of the traditional “open 
system” concept of larval dispersal in the sea 
with computer modeling. Their model suggests 
dispersion can be up to 9 orders of magnitude 
less than would have been predicted from an 
unconstrained model if behavioral and 
additional oceanographic factors are included. 
This difference would yield a far different 
picture of the resulting population, and would 
dictate different management approaches for its 
control and exploitation. These results call for a 
reexamination of the assumptions of fishery 
management models, and could in part explain 
why performance of most fisheries under 
management has been so poor. 
Communication between investigators has 
always been an important part of advancement 
of knowledge. Standardization of terminology 
for description of the environment is a major 
advance in such communication. Just such a 
standardization is made possible by Greene et 
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