Abstract: A Multivariate Statistical Determination of Some Recent Morphospecies of the Genus Elphidium from the Gulf of Mexico

By

Fred E. Fisher
University of Houston, M. S. Thesis, June, 1968.

An analysis involving a set of 15 variables (Text-fig. 4) on each of 212 specimens of the genus Elphidium sub-equally distributed among 7 samples from the northwestern Gulf of Mexico (Text-fig. 1) results in 6 groups which are both observationally and statistically distinct. These 6 groups correspond to 9 previously described species.

The raw data are subjected to the following series of multivariate statistical techniques: 

1. Statistical normalization (z-form) and data condensation (factor analysis)
2. Formation of protogroups and a residual pool of ungrouped specimens (geometric distance)
3. Addition of ungrouped specimens to protogroups and verification of groupings (discriminant analysis)
4. Combination of protogroups (canonical variates of graphical technique)
5. Procedures 3 and 4 are repeated until no more specimens can be added to the protogroups and no more protogroups can be combined. 

The resulting sets of specimens are the final statistical morphospecies.

The original 9 species are reduced to 5 species: (table 12) Elphidium discoidale, E. galvestonense, E. gunteri, E. incertum and E. poeyanum. Elphidium matagordanum is provisionally considered a junior synonym of E. incertum mexicanum; Cribroelphidium poeyanum, Elphidium delicatulum and E. Translucens are provisionally considered junior synonyms of E. poeyanum.

Geographic distributions of the groups in this study indicate that there may be three faunal areas of Elphidium in the Gulf of Mexico: the northern Gulf characterized by E. gunteri, the western Gulf characterized by E. discoidale and E. galvestonense, and the southern Gulf characterized by E. incertum mexicanum.

End_Page 18---------------

Text-fig. 1 - Map showing sample locations, faunal areas (Roman numerals), and percentages of final groups (Arabic numerals) present in each sample.

Text-fig. 2 - Sketch of a generalized Elphidium showing lines of measurement.

End_Page 19---------------

Text-Fig. 4 - Statistical definition of final groups showing the mean (horizontal line), 90% confidence interval on the mean (thick vertical line for each of the 15 variables (ordinates) on each of the 6 group (abscissas). Invariant characters are indicated by circles.

End_Page 20---------------

Table 12. Species Designations.

End_of_Record - Last_Page 21---------------

Copyright © 2005 by Houston Geological Society. All rights reserved.