Key, M. M., Jr. 1991

J. Paleont., 65(2), 1991, pp. 200-212 Copyright ? 1991, The Paleontological Society 0022-3360/91/0065-0200$03.00 THE HALLOPORID TREPOSTOME BRYOZOANS FROM THE ORDOVICIAN SIMPSON GROUP OF OKLAHOMA MARCUS M. KEY, JR. Department of Geology, Dickinson College, P.O. Box 1773, Carlisle, Pennsylvania 17013 ABSTRACT--The Bromide Formation of the Middle Ordovician Simpson Group of Oklahoma contains one of the oldest diverse bryozoan faunas in North America. The early divergence of many trepostome clades is revealed in these rocks. Three trepostome bryozoan species belonging to family Halloporidae are described from this fauna. Discriminant analysis is used to define the following halloporid species: Diplotrypa schindeli n. sp., Tarphophragma karklinsi n. sp., and Tarphophragma macrostoma (Loeblich). Pre- liminary cladistic analysis indicates that the family Halloporidae was already a distinct lineage by the Middle Ordovician. This suggests that by this time, many of the major trepostome clades were already established. INTRODUCTION DISCRIMINANT ANALYSIS THIS STUDY was carried out on Middle Ordovician Simpson Two of the 15 quantitative characters (characters 41-55 in Group outcrops in the Arbuckle Mountains of south-cen- Key, 1990, Appendix 1) were not utilized in the discriminant tral Oklahoma. Geologic setting, location, and measured section analysis. Autozooidal living-chamber cross-sectional diameter descriptions can be found in Key (1990, figs. 1, 2). Material for (character 47) was not used, as this character is better repre- this study came from four stratigraphic sections encompassing sented by autozooidal living-chamber cross-sectional area (char- the Bromide Formation (localities 2-5 in Key, 1990, figs. 1, 2). acter 46), which was included. Character 47 was calculated and Bulk material collections from these sections were made by R. reported so these species could be compared with previously S. Boardman in 1961 and 1962, by Boardman and G. T. Farmer, described species using this character, which has traditionally Jr. in 1963, and by Boardman and J. E. Merida in 1966. The been reported in previous trepostome species descriptions. author collected more material in 1987 to fill in the stratigraphic Number of acanthostyles per mm2 (character 55) was not used gaps in these existing collections. All of the bulk material is in the discriminant analysis as all three of the species lacked housed in the National Museum of Natural History (NMNH), acanthostyles. Bryozoa Stenolaemata General Collection. This left 13 quantitative characters. The data consisted of Prior to this study, 45 halloporid colonies from the Ordovi- these 13 characters measured on 57 colonies belonging to the cian Simpson Group of Oklahoma had been sectioned by Board- three putative species. Each character value was an average of man, Farmer, Loeblich, and Merida. To these the author added up to 10 replicates within each colony. Colony means were another 136 colonies, bringing the total number available for utilized to minimize the effect of nonheritable variation resulting study to 181. All thin sections, acetate peels, and colony rem- from measurement error, varying depths and orientations of nants are housed in the NMNH, Paleozoic Bryozoa Stenolae- sections, and any astogenetic, ontogenetic, polymorphic, and mate thin section collection. Data were collected using trans- microenvironmental variation. mitted light microscopy, thin section projection, and The randomness of data collection was ensured by the random microcomputer-based video image digitizing. Using repeat- selection of colonies and zooids during slabbing of the bulk ability experiments, measurement error was calculated to be 3.8 material. Variances among characters and species were nor- percent. malized by transforming the data into natural logarithms. This required adding 1.0 to all the values of character 51 prior to transformation because of 0.0 values. SPECIES RECOGNITION Discriminant analysis requires that there be no missing values Fifty-five characters were analyzed in this study in the(Key, data 1990, matrix. Initially, this was not the case. The problem Appendix 1). Forty were qualitative multistate characterswas resolved and using two methods, the results from which were 15 were quantitative characters (see Key, 1990, for then a discussioncompared. The first solution involved substituting species of characters). The 40 qualitative multistate characters means for were missing colony mean values. The second solution scored on the 181 colonies. These colonies included involved type-spec- first dropping out the characters with the most missing imen colonies from previously described Middle values Ordovician and then dropping out the colonies with missing values species that were morphologically similar to the halloporidfor any of the spe- remaining characters. cies. The colonies were then qualitatively grouped usingDiscriminant the 40 analysis was performed using the statistical soft- multistate characters into three tentative species. Character ware package states SPSS/PC+ (SPSS, 1988). The maximum number for the three species are listed in Appendix 1. The of stratigraphicdiscriminating functions is the lesser of either the number of ranges and ages of the three species are shown in characters Figure 1. (i.e., The 13 in the first analysis and nine in the second 15 quantitative characters were then measured, counted, analysis) or onecal- fewer than the number of species (i.e., 3 - 1 culated on 57 of the 181 colonies that were most =complete. 2). Thus, the An maximum number of functions in both analyses average of 19 colonies (range 12-24) from each ofwas thetwo. three species was analyzed. Each quantitative character was The measured first analysis (substituting species means for missing val- up to 10 times per colony. One some colonies that ues) were used small, a natural log transformed matrix of 13 characters and fewer than 10 replicates were measured. Finally, the57 colonies qualitative belonging to the three species. Discriminant analysis species groupings were statistically checked with was this able separate to significantly distinguish all three species at P = set of quantitative characters using discriminant 0.0001. analysis. One hundred percent of the colonies were correctly 200 This content downloaded from 64.9.63.163 on Thu, 03 Sep 2020 12:25:32 UTC All use subject to https://about.jstor.org/terms KEY--ORDOVICIAN TREPOSTOMES FROM OKLAHOMA 201 STAGE SERIES FOFRMATION 8 ROCKLANDIAN 6 0 z 2 o BLACKRIVERAN MOHAWKIAN BROMIDE LZ 4 -2-0o0 0 -a -6 o0 CHAZYAN WHITEROCKIAN I -8 -6 1-4 "-2 0 2 4 6 8 10 12 14 S- E FUNCTION 1 THICKNESS - 0o -a + Diplotrypa schindeli o Tarphophragma karklinsi O Tarphophragma macrostoma FIGURE 2--Distribution of the 57 colonies in the first two dimensions co CC of discriminant space. 50]1 Q FIGURE 1--Stratigraphic the most parsimonious chart showing cladogram species (Hendy ranges. and Penny, Modified 1982; from Ross et al. (1982). Swofford, 1985). No a priori assumptions regarding the transformational ordering of character states were made before analysis. By using assigned to their unordered species. characters, The any first character discriminant state could potentially function evolve ex- plained 75.57 percent directly into of any the other variance; state. The ordering character of states 49(i.e., (wallplacing thickness) loaded heavily them in a(-0.74) polarity sequenceon this from function. plesiomorphic The to apomorphic) second discriminant function was done explainedsimultaneously the with remainingthe cladistic analysis 24.43 using percent out- of the variance; character group analysis. 46 (autozooecial living chamber cross- sectional area) loaded Using only heavily one outgroup (0.80) species on can this produce function. misleading char-Therefore, a plot of function acter polarities1 vs. function due to autapomorphic 2 (Figure characters 2) encompasses in that out- 100 percent of the groupvariance species. andTo reduce mainly this problem, separates four speciesthe coloniesof Bimu- based on characters 49 and 46. ropora Key were used. Species of Bimuropora were chosen as The second analysis dropped the four characters with the the most outgroup taxa because they are definitely not members of missing values (46: autozooecial living chamber cross-sectional the ingroup, but they are closely related (Key, 1990). The states area; 50: number of autozooidal diaphragms per mm in ofearly each character for the four outgroup species are also listed in ontogeny; 53: number of mesozooidal diaphragms per mmAppendix in 1. exozone; and 54: number of complete mesozooids per mm2 in outer exozone) and then dropped the colonies with any missing values in the remaining characters. This resulted in a matrix of CLADISTIC RESULTS nine characters and 47 colonies belonging to the three species. Using the 40 multistate characters, cladistic analysis resulted The data were natural log transformed as in the first analysis.in one most parsimonious cladogram with a length of 36 steps Discriminant analysis was able to significantly distinguish and aall consistency index of 0.944 (Figure 3). Figure 3 shows that three species at P = 0.0001, and 100 percent of the colonies the ingroup (family Halloporidae) is monophyletic. Within the were correctly assigned to their species. ingroup, two groups of species are evident; first near the base, Both of these analyses were slightly biased. The first analysis, the least derived species of the ingroup, Diplotrypa schindeli, is which

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