Palaeogeographical patterns in Late Ordovician bryozoan morphology as proxies for temperature

Abstract

Several studies have revealed temperature-related patterns in recent bryozoans, both in the chemical composition of the skeleton and in the morphological characters of the colonies, but comparable studies on Palaeozoic bryozoans are lacking. In this paper a statistical analysis of the morphological differences is undertaken between congeneric species of some Ordovician bryozoans from warm-and cold-water settings. For this study ten eurythermic cosmopolitan bryozoan genera from the Upper Ordovician were selected from the Mediterranean, Avalonia, Baltic and Laurentia-Siberian provinces. These genera are: Ceramopora and Ceramoporella (Cystoporata); Diplotrypa, Eridotrypa, Hallopora, Heterotrypa, Monticulipora and Trematopora (Trepostomata); Graptodictya (Cryptostomata); and Kukersella (Cyclostomata). The study involved 154 samples belonging to 104 different species. Twenty-eight morphological characters were measured, although only 21 were used in the final statistical analysis. Univariate (t, F, Kolmogorov-Smirnov and Mann-Whitney tests), multivariate discriminant and multivariate ordination (Principal Coordinates, Principal Components, Correspondence, and Detrended Correspondence) analyses were performed on the data. For the univariate and multivariate discriminant analyses, the total set of samples was divided a priori into cold-and warm-water subsets based on palaeolatitude: samples from the Mediterranean province were attributed to the cold-water subset, whereas samples from Avalonia, Baltic and the Laurentian-Siberian provinces were included in the warm-water subset. For the multivariate ordination analysis no a priori grouping by water temperature was imposed, and the aim of these analyses was to test whether different samples were correctly arranged along a water temperature gradient. The univariate statistical analysis showed that there are clear morphological differences between cold-and warm-water species in six of the ten Late Ordovician bryozoan genera analysed in this study, although these differences are only evident for some of the characters used, and only when the analysis is performed on individual genera. The best characters to differentiate species by water temperature are those related to the size of the zooidal polymorphs, especially the diameters of the autozooecia, mesozooecia and exilazooecia. With the exception of one genus (Trematopora), cold-water species have larger zooids. The discriminant analysis was able to classify correctly as warm-or cold-water 100% of the samples for two genera, slightly below 95% for two other genera, and between 67% and 90% for the remaining six genera. Finally, the multivariate ordination analysis was able to separate species by palaeogeographical province in some genera, but these provinces were not correctly arranged along a palaeolatitudinal gradient using any of the methods used. • Key words: bryozoans, cosmopolitan genera, latitudinal adaptations, univariate and multivariate statistical analysis.

Ordovician stratigraphy and benthic community replacements in the eastern Anti-Atlas, Morocco

“…In the eastern Atlas Basin, some bryozoan thickets flourished locally on Katian silty carbonates of the Ktaoua Group (Álvaro et al 2007b, 2014aBenharref et al 2014a, b, c). The onset of echinoderm-bryozoan meadows and mud-mounds had been previously reported in Libya (Buttler & Massa 1996;Buttler et al 2007), the Iberian Peninsula (Vennin et al 1998;Jiménez-Sánchez 2009Jiménez-Sánchez & Villas 2010;Jiménez-Sánchez et al 2013) and Sardinia (Conti 1990). The bryozoan assemblages of the upper Katian Khabt-el-Hajar Formation display a diversity close to that documented in the Iberian Chains (Jiménez-Sánchez 2009Jiménez-Sánchez & Villas 2010) and Sardinia (Conti 1990), only surpassed in the southwestern Mediterranean region in the southern Montagne Noire (Ernst & Key 2007) The benthic communities that characterize the Katian-Hirnantian transition cannot be studied in the eastern Anti-Atlas due to the absence of the Lower Formation of the Second Bani Group.…”

Middle Jurassic (Callovian) cyclostome bryozoans from the Tethyan tropics (Matmor Formation, southern Israel)

“…The relationship has been studied extensively in a laboratory setting among conspecific colonies of modern cheilostome bryozoans: "Temperature consistently provides, either directly or indirectly, a pervading and dominant influence on zooid size" (Okamura et al 2011, p. 144). While most data concerns temperature-related differences in zooid size within cheilostome species, or even within colonies, there are indications that the relationship may also operate between species of the same genus (Kukliński & Taylor 2008) and among stenolaemates too (Jiménez-Sánchez et al 2013). Therefore the small zooid sizes of the Matmor cyclostome species may be a function of their development on a warm, tropical shelf.…”

New trepostomate bryozoans from the Upper Ordovician of Morocco and the temperature influence on zooid size

“…Jiménez-Sánchez et al (2013) studied the morphological differences between Upper Ordovician bryozoans living in cold-temperate waters and those living in warm waters, using the paleolatitude as a proxy for water temperature. For that purpose, they studied a total of 154 samples belonging to 104 species assigned to 10 genera included in four orders; the morphological data were statistically analyzed with multivariate discriminant and univariate analysis.…”

“…We also compare the zooecial sizes of the recorded species with other congeneric species from the temperate-cold Mediterranean bryozoan province and the warm Baltic and Laurentian-Siberian bryozoan provinces (Jiménez-Sánchez and Villas, 2010). The aim of this comparison is to test previous results that relate temperature and zooid size, especially among Ordovician trepostomates (Jiménez-Sánchez et al, 2013).…”