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Using MORPHOMETRICS, Phylogenetic Systematics and Parsimony Analysis to Gain Insight into the Evolutionary Affinities of the Calymenidae Trilobita

Chestnut, Alex J.

Abstract Details

2009, Master of Science (MS), Wright State University, Earth and Environmental Sciences.

The most common trilobite in the Silurian carbonates of Ohio – especially the Springfield Dolomite – is a species that has been assigned to at least five genera over the past 100 years. This trilobite has been variously referred to as Calymene celebra, Apocalymene celebra, Flexicalymene celebra, Gravicalymene celebra, and Sthenarocalymene celebra. Reexamination of the species “Calymene” celebra through parsimony and morphometric analysis was conducted to properly place this calymenid species within the correct genus. What compounds the confusion is that the characters used to seperate the genera within the family Calymenidae, and therefore create the basis for the argument to create a new genus, seem weak at best. Coupled with the use of incomplete specimens in the new descriptions, overinflation of genera is not only possible, but a reality.In the past 75 years, the pioneers of trilobite research have labored extensively to classify the family Calymenidae. A major study by Shirley in 1936 attempted to classify the calymenids on the basis of cephalic characteristics – specifically the shape of the glabella, variations in the preglabellar field, and the development of papillate lobes – feeling that other morphological characteristics were conservative at best, and unreliable. Subsequent studies have basically followed Shirley's proposed classifications based upon these objective characters. However, a consistant problem with objective character-based analysis is the subjective nature of description. The purpose of phylogenetic classification (cladistics) is to recognize phylogenetic groups, or taxa, all of whose members are descended from a common ancestor. The common ancestor and all descendents form a monophyletic group. Phylogenetic classification is concerned with grouping individual species into evolutionary categories. Because classification uses both quantitative and qualitative data, the goal was to remove the subjective nature of qualitative data. By using morphometrics to help find similarities within shapes, description of the cephalon can be defined in absolute values instead of subjective descriptions.

Based on quantitative phylogenetic analysis, “Calymene” calymene best fits with Calymene, as originally described by Raymond in 1916. Phylogenetic analysis also indicates that the study genera could be “lumped” into the following generic categories (synonymous genera in parentheses): Alcymene, Calymene (including Calymene celebra), Flexicalymene (including Gravicalymene, Nipponcalymene, Onnicalymene, Metacalymene, and Sthenarocalymene), Diacalymene (including Arcticalymene), Tapinocalymene, and Spathacalymene.

Landmark analysis was used to corroborate the findings of the cladistic analysis. The graphing of Procrutes fitted cephalic landmarks utilizing Principal Component Analysis and Cluster analysis. Landmark analysis indicates that “Calymene” celebra more closely matches with Calymene than the other three study genera to which it has been assigned over the past 100 years. These results directly correlate to the findings in the phylogenetic analysis. As additional specimens are added to the data sets and the groups are rerun, the cluster dendrogram from this group shows “Calymene” celebra to be more similiar to two other species of different genera. As with the previous data set, Alcymene, Arcticalymene, Spathacalymene, and Tapinocalymene are outside the main “nesting” arrangement and can be considered different enough to warrant separate generic assignments. However, the remainder of the specimens are too closely nested to warrant individual generic assignment.

When we look at the same data set as used in the cladistic analysis – to include only “Calymene” celebra and all genera in the study – the results mirror those when “Calymene” celebra is compared to all samples in the study. It was determined that as more samples were added, “Calymene” celebra becomes clustered/nested with different genera and/or species, indicating that the morphological differences between them is not significant enough to warrant division. Analysis of the scatter plots from the Principal Component Analysis of the study genera and “Calymene” celebra show that “Calymene” celebra always plots closer to Calymene than any other genus. In some analyses, they share the same statistical space indicating strong statistical similarities. Because of the strong correlation between both results, we can infer that “Calymene” celebra is best assigned to the genus Calymene, as first described by Percy Raymond in 1916.

The question remains, what amount of characteristic differences warrant a new genus. Genera should not defined not by one character, but by a group of carefully chosen characters, and in cases where modifications are slight, it is more logical to revise the genus than to create a completely new genus. This would lead us to think that within the genera Calymene, Flexicalymene, Apocalymene, Gravicalymene, and Sthenarocalymene, as well as others, the morphological characteristics – and modifications of those characteristics – are slight enough that assignment of new genera, as seen over the years was unwarranted.

Charles Ciampaglio, PhD (Advisor)
Charles Ciampaglio, PhD (Committee Co-Chair)
Ernest Hauser, PhD (Committee Co-Chair)
Loren E. Babcock, PhD (Committee Member)
Christopher Barton, PhD (Committee Member)
108 p.

Recommended Citations

Citations

  • Chestnut, A. J. (2009). Using MORPHOMETRICS, Phylogenetic Systematics and Parsimony Analysis to Gain Insight into the Evolutionary Affinities of the Calymenidae Trilobita [Master's thesis, Wright State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=wright1239724101

    APA Style (7th edition)

  • Chestnut, Alex. Using MORPHOMETRICS, Phylogenetic Systematics and Parsimony Analysis to Gain Insight into the Evolutionary Affinities of the Calymenidae Trilobita. 2009. Wright State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=wright1239724101.

    MLA Style (8th edition)

  • Chestnut, Alex. "Using MORPHOMETRICS, Phylogenetic Systematics and Parsimony Analysis to Gain Insight into the Evolutionary Affinities of the Calymenidae Trilobita." Master's thesis, Wright State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1239724101

    Chicago Manual of Style (17th edition)