ARENS, N.C.*, A. THOMPSON, L. CHENG, A. FRUMES, J. HSU, J. LEE, and S. NOSRATINIA. Department of Integrative Biology, 3060 VLSB, Berkeley, CA 94720-3140 USA. - A morphometric method for parataxa delimitation in Quercus of the Neogene.
Delimiting meaningful parataxa in dispersed dicot leaf floras is among
paleobotany’s greatest methodological challenges. Neogene oaks present
a particularly thorny problem because of their morphological
variation. Nonetheless, biologically meaningful assessments of
taxonomic richness are essential to a variety of studies including
those focusing on diversification of clades and paleoclimate
reconstruction. To develop a repeatable method for delimiting taxa
from a mixed collection like those in the fossil record, we assembled
leaves from vouchered herbarium specimens from three co-occurring and
morphologically similar California oaks: Quercus agrifolia Nee,
Q. chrysolepis Liebm., and Q. wislizenii A.DC. For each
leaf, we took digital images, measured 11 quantitative variables, and
calculated five derived variable. These variable have been used to
diagnose parataxa in Neogene oaks. ANOVA also showed that length,
width, length/width, and average secondary vein distance showed
statistically significant difference among species. However, no single
variable distinguished all three species. Discriminant analysis
correctly assigned 82% of the specimens to species. This analysis
shows that (1) a quantitative morphometric analysis can be useful in
delimiting leaf paraspecies within oaks, and (2) that some portion of
any fossil collection is likely to remain in the morphological overlap
between parataxa. A morphometric approach will help refine diagnoses
of fossil leaf parataxa to include quantitative and empirical ranges
of variation. To demonstrate this approach, we performed the reverse
analysis on a large sample of Middle Miocene oaks from the Mint Canyon
Formation of southern California. Multivariate ordination suggests
extensive overlap in morphology among the oaks in this collection.
Only two taxa, rather than the three originally described, can be
conservatively recognized from this collection.
Key words: leaf morphology, morphometrics, Neogene, Quercus