New paleomagnetic data from Permian red beds and Middle Jurassic limestones from the Tarim Basin pose a paradox. Their declinations are similar to Upper Carboniferous to Neogene rocks collected from the same sections, and their inclinations parallel present values. When assuming that lower than expected inclinations in continental sedimentary rocks arise from inclination shallowing effects, then the paleolatitudes of all Upper Carboniferous to Present rocks from Tarim are indistinguishable. Local vertical axis block rotations occurring in the last 20 million years explain why declinations vary at different localities in the basin. Our Middle Jurassic data positions Tarim 23.6 ± 8.4° farther south than that predicted from the coeval reference pole for Eurasia; however, no geologic argument exists to support the closure of a large ocean basin between Tarim and Siberia since the Middle Jurassic. Thus the paradox: are the rocks from Tarim totally overprinted, or is the middle Mesozoic part of the reference Eurasian apparent polar wander path erroneous? Several lines of evidence suggest the Tarim rocks are not remagnetized. We conclude that Tarim has experienced little or no apparent polar wander since the Carboniferous. Moreover, our Middle Mesozoic reconstruction of Eurasia using the new Middle Jurassic pole from Tarim results in a more geologically compatible solution for the eastern Asian blocks over previous reconstructions.

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.