Alan Lord

The Cretaceous-Tertiary biotic transition

Mass extinctions are recognized through the study of fossil groups across event horizons, and from analyses of long-term trends in taxonomic richness and diversity. Both approaches have inherent flaws, and data that once seemed reliable can be readily superseded by the discovery of new fossils and/or the application of new analytical techniques. Herein the current state of the Cretaceous-Tertiary (K-T) biostratigraphical record is reviewed for most major fossil clades, including: calcareous nannoplankton, dinoflagellates, diatoms, radiolaria, foraminifera, ostracodes, scleractinian corals, bryozoans, brachio-pods, molluscs, echinoderms, fish, amphibians, reptiles and terrestrial plants (macrofossils and palynomorphs). These reviews take account of possible biasing factors in the fossil record in order to extract the most comprehensive picture of the K-T biotic crisis available. Results suggest that many faunal and floral groups (ostracodes, bryozoa, ammonite cephalopods, bivalves, archosaurs) were in decline throughout the latest Maastrichtian while others (diatoms, radiolaria, benthic foraminifera, brachiopods, gastropods, fish, amphibians, lepidosaurs, terrestrial plants) passed through the K-T event horizon with only minor taxonomic richness and/or diversity changes. A few microfossil groups (calcareous nannoplankton, dinoflagellates, planktonic foraminifera) did experience a turnover of varying magnitudes in the latest Maastrichtian-earliest Danian. However, many of these turnovers, along with changes in ecological dominance patterns among benthic foraminifera, began in the latest Maastrichtian. Improved taxonomic estimates of the overall pattern and magnitude of the K-T extinction event must await the development of more reliable systematic and phylogenetic data for all Upper Cretaceous clades.

Benthic ostracods and deep water-masses in the Atlantic Ocean

Ostracod faunas at six locations are compared, and related to distributions in an Atlantic Ocean-wide data base. Five, widely developed, vertical faunal sequences are recognised at particular levels within deep water-masses: Henryhowella Fauna (lower part of Antarctic Intermediate Water); Krithe Fauna (Upper North Atlantic Deep Water); Poseidonamicus-Bosquetina Fauna (upper part of Lower NADW); Dutoitella Fauna (lower part of Lower NADW); Legitimocythere Fauna (Antarctic Bottom Water). These faunas are correlated with previously established deep water benthic foraminiferal assemblages, and their possible palaeo-oceanographic use is discussed.

Lower Jurassic Foraminifera and Calcified Microflora from Gibraltar, Western Mediterranean

Benthic foraminifera are described for the first time from the Gibraltar Limestone Formation of the Rock of Gibraltar. The new species Siphovalvulina colomiS. gibraltarensisRiyadhella praeregularis occur with Duotaxis metula Kristan, Everticyclammina praevirguliana Fugagnoli, Siphovalvulina sp.,an atypically early example of Textulariopsis sp., and Nodosaria sp. Microflora are present as the probable cyanobacterium Cayeuxia ?piae Frollo, the alga Palaeodasycladus ?mediterraneus (Pia), and the disputed alga Thaumatoporella ?parvovesiculifera (Raineri). The foraminifera compare most closely with poorly-known taxa from Italy, Spain and Morocco, and are consistent with an Early Jurassic (Sinemurian) age for the upper part of the &62;460-m-thick Gibraltar Limestone. Most are textulariids and more primitive than species well known from the later Early Jurassic (Pliensbachian) of the Mediterranean region, especially Morocco and Italy. The biota as a whole is characteristic of inner carbonate platform environments widespread along the rifted western margins of the Early Jurassic Tethys, notably those recorded from Morocco, Italy and Greece as well as southern Spain.

Ostracoda of the Early Jurassic Tethyan Ocean

The occurrence of ostracods in the Tethyan Ocean during early Jurassic times is reviewed with special reference to assemblage compositions in relation to contemporary geographical and oceano-graphical conditions. The Tethyan material is compared with the well-known and diverse early Jurassic assemblages from Northern and Western Europe and also with Triassic Tethyan ostracods. Particular attention is paid to the temporal and spatial distribution of (a) ornate bairdiids, (b) vallate healdiids, and (c) cytheracean species.

Calcareous nannoplankton biozonation of the Thanetian Stage (Palaeocene) in the type area

The Thanetian Stage in the type area is composed of the Thanet Formation, the Woolwich Bottom Bed and the Oldhaven Beds. The Thanet Formation at the stratotype localities in southeastern England contains calcareous nannoplankton Zones NP 6/7 and NP 8. The Woolwich Bottom Bed and Oldhaven Beds are not zonable in the type area. The marine “Bottom Bed” of the Woolwich and Reading Beds is, however, assignable to Zone NP 9 outside the type area (at Clarendon Hill in Wiltshire).

The extinction of the Metacopina (Ostracoda)

The extinction of the Suborder Metacopina in the early Toarcian (Early Jurassic) was a major event in the macro-evolutionary history of the Ostracoda. The disappearance of this long-ranging, essentially Palaeozoic, group coincides with a change in the composition of marine ostracod faunas from ones with residual Palaeozoic aspect in the pre-Toarcian (due to the presence of the Metacopina) to those dominated by the Cytheroidea, Cypridoidea and Platycopina, a pattern that continues to the present. The Metacopina had been present in many Palaeozoic assemblages although usually at low diversity and abundance but they were particularly successful in Triassic and Early Jurassic times, being diverse, abundant and with an apparently cosmopolitan distribution. Why did such a successful group that had survived four of the ’Big Five’ Phanerozoic extinction events (end Ordovician, Late Devonian, end-Permian, end-Triassic), succumb at this second order and apparently less significant early Toarcian event? The rapid decline and extinction of the Metacopina followed a major regressive phase in the Pliensbachian and broadly coincided with the onset of the early Toarcian Oceanic Anoxic Event (TOAE), which has been linked to global eustatic sea-level rise and is marked by a major, negative carbon isotope (δ13C ) excursion in the global carbon cycle. The nature and likely causes of the Metacopina extinction event (MEE) are reviewed in the context of new environmental data for the Toarcian, with particular reference to evidence from the Mochras Borehole (West Wales) ; the group’s survival of earlier biotic events is also discussed. The one distinct feature that sets the Toarcian extinction event apart from previous evolutionary crises is that the Metacopina never had to compete against relatively advanced ostracod, largely cytheroidean, taxa that were present during the Early Jurassic. We propose that this may have been a key factor in the demise of the Metacopina at this particular time.

THE EVOLUTION OF LEPIDOCYCLINA (L.) ISOLEPIDINOIDES, L. (NEPHROLEPIDINA) NEPHROLEPIDINOIDES SP. NOV., L. (N.) BROUWERI AND L. (N.) FERREROI IN THE LATE OLIGOCENE–MIOCENE OF THE FAR EAST

Material from Borneo and Sumatra show that there is a morphological evolution from Lepidocyclina (Lepidocyclina) isolepidinoides van der Vlerk, 1929, to L. (Nephrolepidina) nephrolepidinoides sp. nov., L. (N.) brouweri Rutten, 1924 and L. (N,) ferreroi Provale, 1909, The lineage demonstrates one of the evolutionary progressions from Lepidocyclina (Lepidocyclina) to Lepidocyclina (Nephrolepidina) for the Far East region.

Chapter 3 - Ostracod Taxa as Palaeoclimate Indicators in the Quaternary

Abstract We review the utility of ostracods for palaeoclimatic reconstruction at different taxonomic levels. Ostracods can provide palaeoenvironmental information based on several approaches. The chemical and isotopic composition of their mineral shells as well as the relatively minor organic component trapped within the carbonate lattice may give direct quantitative evidence of conditions in their natural habitat. Morphological observations and detailed morphometric records of valve size, shape and outline within a species may provide subtle clues to environmental changes between different habitats or adjacent stratigraphic intervals. Uniformitarian approaches can be applied to species, genera and supra-generic classifications but with decreasing resolution and increasing uncertainty in palaeoenvironmental significance (1) the higher the taxonomic unit and (2) the older the material geologically. The classical methodology of combining the habitat and environmental preferences of individual species to infer palaeoclimatic conditions remains as valid today as when such observations were first made in the nineteenth century.

The biostratigraphy of the Upper Pliensbachian-Toarcian (Lower Jurassic) sequence at Ilminster, Somerset

Temporary road sections for the A303 bypass at Ilminster, Somerset, revealed Upper Pliensbachian and Toarcian sediments from an alternating limestone–marl facies, in marked contrast to the limestone-dominated Dorset coast succession. The lithostratigraphy is described, with the standard ammonite zonation providing chronostratigraphical correlation. The uppermost Pliensbachian (Spinatum Chronozone) and much of the Toarcian (Serpentinum, Bifrons, Variabilis, Thouarsense and Pseudoradiosa chronozones) of the classic Dorset coast Lower Jurassic sequence are represented by the Beacon Limestone Formation, formerly the ‘Junction Bed’ (a highly condensed carbonate deposit). The Tenuicostatum Chronozone is largely missing from the sequence. Elsewhere in southern and eastern England this interval is poorly or rarely exposed. The argillaceous units have yielded rich microfaunas and -floras (foraminifera, ostracods, calcareous nannofossils and palynomorphs), the biostratigraphical distributions of which are analysed and discussed in relation to contemporary evolutionary patterns and other UK records. This study provides an insight into the micro-biostratigraphy of the Late Pliensbachian to Toarcian interval for onshore southern England.

Cyprideis torosa: a model organism for the Ostracoda?

In 1990 Danielopol et al. described the ostracod genus Cytherissa as ‘the Drosophila of paleolimnology’ in the sense of a model organism for their purposes at that time. In the intervening years Drosophila is no longer seen by biologists as the perfect test model and, for example, the nematode worm Caenorhabditis elegans is now viewed as preferable because ‘the fly is much more complex than the worm and the anatomy of the nervous system has not reached the level of completeness achieved for the worm’ (Brenner 2003, p. 278). For some years attention has focused on Cyprideis torosa (Jones, 1850), especially since the pioneering work of Rosenfeld & Vesper (1977) on sieve-pore variability in this species in relation to salinity, because torosa is a particularly widely distributed euryhaline living and fossil ostracod species. Cyprideis torosa is not only biogeographically widespread but occurs in a salinity range from freshwater to hypersaline, tolerates a wide range of temperature, oxygen and substrate conditions, and also has a large, well-calcified and easily preserved carapace. The species first occurs in sedimentary formations of early Pleistocene age but may be older. Therefore, it has the potential to be an ostracod model organism. This set of thematic papers is designed to summarize our current knowledge of one of the most important living ostracod species, its distribution, ecology, morphological response to environmental pressures, and molecular characterization, together with our understanding of its origins and value for palaeoenvironmental interpretation. The ultimate aim is to define potentially rewarding research targets using C. torosa as a model organism.