Figure 1.
‘Sandbian time slab’ (shaded).
Between the first appearance of N. gracilis and the beginning of the D. clingani graptolite Biozone. Graptolite ranges follow [82]–[86]. The conodont data are from [50] and chitinozoans are from [87]. The correlation between the graptolite, conodont, and chitinozoan biozones follows [63].
Figure 2.
Ordovician chronostratigraphy and lithostratigraphy for North America, Canada, and the Girvan district, southwest Scotland.
The North American stratigraphy follows [88], Canadian stratigraphy follows [89] and Girvan is based on [46], [90]. The Sandbian sections from which ostracods are documented and included in this study are highlighted grey.
Figure 3.
Late Ordovician (Sandbian) palaeogeography of Laurentia, the distribution of ostracod-bearing localities, and the two faunal provinces (map slightly modified after [22]).
Figure 4.
Correspondence Analyses (CA) of the (a) entire Sandbian, (b) late Sandbian (bicornis time slab) and (c) early Sandbian (gracilis time slab).
Midcontinent Province localities are shown as filled circles, southern Marginal Province localities as empty circles. Grey polygons indicate the southern Marginal Province localities. For sample labels, see Table S1 and Figure 2.
Figure 5.
Late Ordovician ostracods of the Midcontinent and Marginal provinces and widespread (pandemic-Laurentian) assemblages of palaeocontinental Laurentia.
(A–C) Sandbian Midcontinent Province assemblage; (D–L) Sandbian ostracod assemblage widespread in both the Midcontinent and Marginal provinces; (M) Sandbian Marginal Province assemblage; (N–R) Katian Marginal Province assemblage. (A) NMH UK OS13634 Punctaparchites rugosus (Jones, 1858) [91], carapace, right lateral view. (B) NMH UK OS13479 Winchellatia longispina Kay, 1940 [37], tecnomorphic right valve, lateral view. (C) MCZ 4646 Krausella calvini (Kay, 1940) [37], carapace right lateral view. (D) NMH UK OS13509 Eurychilina indivisa Levinson, 1961 [49], juvenile tecnomorphic right valve, lateral view. (E) NHM UK OS I13216 Eurychilina reticulata Ulrich, 1889 [92], heteromorphic right valve, lateral view. (F) NMH UK OS13535 Hallatia labiosa (Ulrich, 1894) [35] tecnomorphic right valve, lateral view. (G) NMH UK OS13617 Balticella deckeri (Harris, 1931) [38], carapace, right lateral view (H) MCZ 4599b Eohollina depressa (Kay, 1940) [37], tecnomorphic carapace, right lateral view (I) NMH OS13538 Eurybolbina bispinata (Harris, 1957) [23], juvenile tecnomorphic left valve, lateral view. (J) NMH UK OS13526 Eoaquapulex socialis (Levinson, 1961) [49] tecnomorphic left valve, lateral view. (K) BGS GSE 15387 Baltonotella parsispinosa (Kraft, 1962) [26], carapace, left valve, lateral view (L) BGS GSE 15385 Krausella variata Kraft, 1962 [26], right valve, lateral view. (M) BGS GSE 15384 ‘Ctenobolbina’ ventrospinosa Kraft, 1962 [26], heteromorphic, left valve, lateral view. (N) BGS 16E1961 Oepikella tunnicliffi Williams & Floyd, 2000 [93], heteromorphic right valve, lateral view. (O) MPA49672, Balticella sp., carapace, left lateral view. (P) BGS GSE15354 Steusloffina cuneata (Steusloff, 1895) [94], carapace, left lateral view. (Q) BGS GSE15360, Longiscula cf. perfecta Meidla, 1993 [95], carapace, left lateral view. (R) BGS GSE15365, Longiscula cf. tersa (Neckaja, 1966) [96], carapace, right lateral view. Figures (A–D, F–H, J) are from the Bromide Formation of Oklahoma; (E) is from St. Paul's Minnesota; (I) is from the Edinburg Formation of Virginia (K–M) are from the Ardwell Farm Formation, Girvan district, Scotland; (N–R) are from the Craighead Limestone Formation, Girvan district, Scotland. Scale bar (A) 210 µm; (B) 250 µm; (C) 294 µm; (D) 338 µm; (E) 320 µm; (F) 193 µm; (G) 205 µm; (H); 346 µm; (I) 346 µm; (J) 545 µm; (K–M, O, P) 500 µm; (N) 1000 µm; (Q, R) 200 µm. Repositories for specimens are: NHM, Natural History Museum, London; MCZ Museum of Comparative Zoology, Harvard University; BGS GSE, British Geological Survey, Keyworth, Nottingham.