788 THE STRUCTURE OF EVOLUTIONARY THEORY
need not always humble themselves before the power of neontological genetic
analysis of biospecies—Jackson and Cheetham (1990) p. 582) make an empirical
observation about the capacity of morphometric data (of the sort generated from
fossils):
The identity of quantitatively defined morphospecies of cheilostome
bryozoans is both heritable and unambiguously distinct genetically. The
importance of rigorous quantitative analysis was underlined by our
discovery of three species of Stylopoma previously classified as one, a
separation subsequently confirmed genetically. The widely supposed lack
of correspondence between morphospecies and biospecies may result as
much out of uncritical acceptance of outdated, subjectively defined taxa as
from any fundamental biologic differences between the two kinds of
species.Jackson and Cheetham (1994) then followed this study with a more extensive
documentaiton, this time using large numbers of fossil species as well as living
forms, of phylogenetic patterns in two Caribbean cheilostome genera, Stylopoma
(included in the first study as well), and Metrarabdotos (the subject of Cheetham's
earlier and elegant affirmations of punctuated equilibrium from morphometric data
alone—Cheetham, 1986 and 1987, and extensively discussed on pp. 867-870).
Again, and for both genera, they found strict correspondence between genetically
defined clusters and taxa established by skeletal characters accessible from fossils.
With increased confidence that the taxa of his classical studies on punctuated
equilibrium in Metrarabdotos represent true biospecies, Cheetham (now writing
with Jackson) could affirm his earlier work (Jackson and Cheetham, 1994, p. 420):
"Morphological stasis over millions of years punctuated by relatively sudden
appearances of new morphospecies was demonstrated previously for
Metrarabdotos. Our updated results strengthen confidence in that pattern, with 11
morphospecies persisting unchanged for 2-6 m.y., all at p > 0.99, and no evidence
that intraspecific rates of morphological change can account for differences
between species."
For Stylopoma, where fossil evidence had not previously been analyzed
morphometrically, results also affirmed punctuated equilibrium throughout (1994,
p. 420): "The excellent agreement between morphologically and genetically
defined species used in this taxonomy suggests that morphological stasis reflects
genuine species survival over millions of years, rather than a series of
morphologically cryptic species. Moreover, eleven of the 19 species originate fully
formed at p > 0.9, with no evidence of morphologically intermediate forms, and all
ancestral species but one survived unchanged all with their descendants."
In a concluding paragraph about both genera, Jackson and Cheetham wrote
(p. 407): "Stratigraphically rooted trees suggest that most well-sampled
Metrarabdotos and Stylopoma species originated fully differentiated
morphologically and persisted unchanged for > 1 to > 16 m.y., typically