Review and palaeoecological analysis of the late Tremadocian - early Floian (Early Ordovician) cephalopod fauna of the Montagne Noire, France

Abstract

HS‐26, the mouse homologue of HS‐40, is the major regulatory element of the mouse α‐globin gene locus. Like HS‐40, HS‐26 is located within an intron of a house‐keeping gene; comparison of the nucleotide sequences of HS‐26 and HS‐40 reveals conservation of the sequences and positions of several DNA binding motifs in the 5′ regions of both elements (3 GATA, 2 NFE‐2, and 1 CACCC sites) and the absence in HS‐26 of three CACCC sites and one GATA site that are present in the 3′ region of HS‐40, suggesting that the two elements might not be identical. We report here that when HS‐26 is linked to a 1.5 kb Psti human α‐globin gene fragment, it has a weak enhancer activity in induced MEL cells and in transgenic embryos, and it does not have any detectable activity in adult transgenic mice. This suggests that HS‐26 does not have Locus Control Region (LCR) activity but can act as an enhancer during the embryonic life when integrated at a permissive locus. To further test the importance of HS‐26 at its natural locus, we have generated embryonic stem cells and chimeric animals in which 350 bp containing HS‐26 have been replaced by a neomycin resistance gene by homologous recombination. The sizes of the chimeras' red cells were then estimated by measuring forward scattering on a FacsScan apparatus in hypotonic conditions. This revealed that a fraction of the chimeric animals' red cells were smaller than normal mouse red cells and were very similar to cells from mice heterozygous for α‐thalassemia. Density gradient analysis also suggested the presence of thalassemic cells. These results indicated that despite its lack of LCR activity, HS‐26 is important for the regulation of the mouse α‐globin gene locus. Am. J. Hematol. 54:30–39, 1997 © 1997 Wiley‐Liss, Inc.

A revision of the Ordovician cephalopod Bactrites sandbergeri Barrande: Systematic position and palaeobiogeography of Bactroceras

“…This group includes pelagic cephalopods that, owing to their morphology, were able to expand from their original, demersal niches to pelagic and deep-water realms. Soon, orthocerids became highly diversified and geographically widespread (Frey, 1995;Krö ger and Mutvei, 2005; and Evans, 2011;Evans et al, 2013;Krö ger, 2013). Consequently, understanding the origin of Bactroceras, its evolution, and the divergence of allied lines are crucial for elucidating the still poorly-known early radiation of orthocerid cephalopods.…”

“…with the genus Annbactroceras, are the earliest known orthocerid cephalopods (Krö ger and Evans, 2011). This group includes pelagic cephalopods that, owing to their morphology, were able to expand from their original, demersal niches to pelagic and deep-water realms.…”

Palaeogeography and palaeoecology of early Floian (Early Ordovician) cephalopods from the Upper Fezouata Formation, Anti-Atlas, Morocco

“…Bactroceras, Rioceras are known from both the Montagne Noire and the Anti-Atlas. These two genera appear to be a common element of several Early Ordovician Gondwanan cephalopod associations, further supporting the socalled "Saloceras-realm" (Kraeger & Evans 2011). Potentially, Bathmoceras australe Teichert, 1939, which occurs in Australia and possibly in Argentina (see below), Polymeres, which otherwise is known from early Floian sediments of Wales (Evans 2005), and Protocyptendoceras, which is known now from Morocco and Argentina (Cichowolski 2009) are additional elements of the Saloceras-realm.…”

“…A similar taphonomic scenario was interpreted in the same way by Hewitt & Westermann (1996, fig. 8, scenario 2b) and in Kraeger & Evans (2011) for Ordovician and Silurian orthocone dominated environments. The frequent fragmentation of the conchs indicates some reworking or transport of the dead shells.…”

“…Generally, the Ordovician cephalopods of the high latitude margins of Gondwana are poorly known and, where known, often are in need of revision. Of those high latitudinal assemblages most recently revised or newly described in detail (Marek et al 2000;Gnoli & Pillola 2002;Evans 2005;Kraeger & Evans 2011), all seem to be characterized by the presence (often in abundance) of specific forms that are rare or absent in low palaeolatitude regions.…”