The history of Devonian-Carboniferous reef communities: Extinctions,effects, recovery

Summary Analysis of the taxonomic composition, diversity and guild structure of five “typical” reef and mud mound communities ranging in age from Late Devonian-Early Carboniferous indicates that each of these aspects of community organization changed dramatically in relation to three extinction events. These events include a major or mass extinction at the end of the Frasnian; reef communities were also effected by less drastic end-Givetian and mid-late Famennian extinctions of reef-building higher taxa. Peak Paleozoic generic diversities for reef-building stromatoporoids and rugose corals occurred in the Eifelian-Givetian; reef-building calcareous algal taxa were longranging with peak diversity in the Devonian. These three higher taxa dominated all reef-building guilds (Constructor, Binder, Baffler) in the Frasnian and formed fossil reef communities with balanced guild structures. The extinction of nearly all reef-building stromatoporoids and rugose corals at the end of the Frasnian and the survival of nearly all calcareous algac produced mid-late Famennian reef communities dominated by the Binder Guild. Despite the survival of most calcareous algae and tabulate corals, the mid-late Famennian extinction of all remaining Paleozoic stromatoporoids and nearly all shelf-dwelling Rugosa brought the already diminished Devonian reef-building to a halt. These Devonian extinctions differ from mass extinctions by the absence of a statistically significant drop in taxonomic diversity and by their successional and cumulative effects on reef communities. Tournaisian mud mounds contain communities markedly different from the frame-building communities in Late Devonian and Visean reefs. Mound-building biotas consist of an unusual association dominated by erect, weakly skeletonized members of the Baffler Guild (chiefly fenestrate Bryozoa; Pelmatozoa) and laterally expanded, mud-binding algae/stromatolites and reptant Bryozoa. The initial recovery to reefs with skeletal frameworks in the Visean was largely due to the re-appearance of new species of abundant colonial rugose corals (Constructor Guild) and fenestrate Bryozoa. This Frasnian-Visean evolution in the taxonomic composition and structure of the reef-building guilds is also expressed by abrupt changes in biofacies and petrology of the reef limestones they produced. Thus, “typical” Frasnian reef limestones with balanced guild structures are framestones-boundstones-bafflestones, Famennian reefs are predominantly boundstones, Tournaisian mud mounds are bafflestones and Visean reefs are bafflestones-framestones.     

The barbs (Barbus spp.) of Lake Tana: a forgotten species flock?

Synopsis All living species occupy an ecological niche, and are positioned within a trophic hierarchy. Extinct organisms presumably held similar behavioral and coevolutionary characteristics in the past, and were susceptible to the same kinds of natural ecological pressures operating today. Paleoecological investigations are limited by the incompleteness of the fossil record, and particularly by a lack of behavioral data that are so fundamental to ecological studies of living communities and habitats. Opportunities to examine the coevolutionary structure of ancient communities from empirical data are extremely rare. One such opportunity is provided by the Lower Cretaceous Santana Formation of north-eastern Brazil, a series of richly fossiliferous strata approximately 110 million years old. Many fossil fishes from the Santana Formation contain identifiable prey, including decapod crustaceans and fishes. A trophic hierarchy of these organisms is reconstructed here, and their ecological relationships are discussed. Comparison is made with a similar fish fauna from the Upper Jurassic Solnhofen Limestone of Germany. Low-level, intermediate and high-level predators are identified in each fauna. Predator-prey relationships in the Santana fauna are strongly hierarchical, and are more focussed at the intermediate predator level than in Solnhofen. Comparison with a model of predator-prey relationships between fishes and benthic fauna of the Baltic Sea (which like the Araripe Basin represents a semi-enclosed environment) suggests that heavy predation on teleosts such asRhacolepis, occupying an intermediate trophic level, may have permitted benthic decapods to proliferate and exclude other benthic organisms. Less intense predation on fishes at the intermediate trophic level would allow their numbers to increase, thereby increasing the intensity of predation on the benthos at the base of the trophic hierarchy.     

Upper cretaceous rudist and stromatoporid associations of Central Oman (Arabian Peninsula)

Summary Rudist and stromatoporid associations of the Campanian from Central Oman are nearly monospecific. They are dominated byDurania aff.nicholasi, Vaccinites vesiculosus, Torreites milanovici or phaceloid and massive stromatoporids. Several other rudist genera play a secondary role. The thickness of the associations is rarely more than one metre. Solitary corals do not occur in the associations. Colonial corals are less common, although they are up to 1 m high and show considerable diversity. There are no binders. The reef structure indicates variable hydrodynamic conditions. They are always associated with very shallow water. The pureDurania aff.nicholasi patches with large colonial corals andTorreites milanovici are presumably the most rigid structures. The near monospecific associations ofVaccinites vesiculosus are widely distributed. Although mostly preserved in situ, strong currents, presumably caused by tropical storms, have repeatedly impaired and interrupted growth. The specific growth characteristics of the shell of some rudists, especially the radiolitids, enable an estimation of the individual lifespan. Frameworks of approximately 1 metre thickness probably developed in ±100 years. The sediments of the complete sections are predominantly bioclastic.     

Paleoecology of Upper Eifelian and Lower Givetian coral limestones in the northwestern Sauerland (Devonian; Rhenish Massif)

Summary The prevailing sandy/silty lower part of the Middle Devonian in the northwestern Sauerland includes two coral limestone horizons, which contain a rich fauna of corals, stromatoporoids, and calcareous algae. The Ihmert-Formation is subdvided into three parts. The older coral limestone horizon is the Grünewiese-Member of the Ihmert-Formation (uppermost Eifelian), the younger is in the Bredenbruch-Member of the Unterhonsel-Formation (lower Lower Givetian). Conclusions about the environmental constraints are drawn from the sedimentology and the fossil content of the coral limestones. Predominant biostromes are built between storm wave base and normal wave base. Only the few bioherms grew above the normal wave base. These coral limestones were deposited in a tropical or subtropical normal marine environment in the shallow euphotic zone. Among the reef-builders epoecism is very frequent, and until now this phenomenon has not been investigated in detail. Fragile rugose and tabulate corals lived as commensals with stromatoporoids. Some other aspects of paleoecology are concisely presented.     

Le Crocodilien Diplocynodon (Eusuchia,Alligatoridae) dans la«série du gypse d'Aix à Venelles (Bouches-du-Rhône,France)

A crocodilian skeleton from the «série du gypse d'Aix (basal Aquitanian) at Venelles (Bouches-du-Rhône) is described and referred to Diplocynodon cf. rateli. The specimen seems to have been mutilated by scavengers before burial. The occurrence of the freshwater crocodilian Diplocynodon in the «série du gypse d'Aix is in agreement with recent reconstructions of the depositional environment, which suggest a basin with a fluctuating, but usually low, salinity.     

Way out of Africa: Early Pleistocene paleoenvironments inhabited by Homo erectus in Sangiran, Java

A sequence of paleosols in the Solo Basin, Central Java, Indonesia, documents the local and regional environments present when Homo erectus spread through Southeast Asia during the early Pleistocene. The earliest human immigrants encountered a low-relief lake-margin landscape dominated by moist grasslands with open woodlands in the driest landscape positions. By 1.5 Ma, large streams filled the lake and the landscape became more riverine in nature, with riparian forests, savanna, and open woodland. Paleosol morphology and carbon isotope values of soil organic matter and pedogenic carbonates indicate a long-term shift toward regional drying or increased duration of the annual dry season through the early Pleistocene. This suggests that an annual dry season associated with monsoon conditions was an important aspect of the paleoclimate in which early humans spread from Africa to Southeast Asia.     

Shell Beds as paleoecological puzzles: A case study from the Upper Permian of the Paraná Basin, Brazil

Summary Microstratigraphic, sedimentological, and taphonomic features of the Ferraz Shell Bed, from the Upper Permian (Kazanian-Tatarian?) Corumbataí Formation of Rio Claro Region (the Paraná Basin, Brazil), indicate that the bed consists of four distinct microstratigraphic units. They include, from bottom to top, a lag concentration (Unit 1), a partly reworked storm deposit (Unit 2), a rapidly deposited sandstone unit with three thin horizons recording episodes of reworking (Unit 3), and a shell-rich horizon generated by reworking/winnowing that was subsequently buried by storm-induced obrution deposit (Unit 4). The bioclasts of the Ferraz Shell Bed represent exclusively bivalve mollusks.Pinzonellaillusa andTerraia aequilateralis are the dominant species. Taphonomic analysis indicates that mollusks are heavily time-averaged (except for some parts of Unit 3). Moreover, different species are time-averaged to a different degree (disharmonious time-averaging). The units differ statistically from one another in their taxonomic and ecological composition, in their taphonomic pattern, and in the size-frequency distributions of the two most common species. Other Permian shell beds of the Paraná Basin are simílar to the Ferraz Shell Bed in their faunal composition (they typically contain similar sets of 5 to 10 bivalve species) and in their taphonomic, sedimentologic, and microstratigraphic characteristics. However, rare shell beds that include 2–3 species only and are dominated by articulated shells preserved in life position also occur. Diversity levels in the Permian benthic associations of the Paraná Basin were very low, with the point diversity of 2–3 species and with the within-habitat and basin-wide (alpha and gamma) diversities of 10 species, at most. The Paraná Basin benthic communities may have thus been analogous to low-diversity bivalve-dominated associations of the present-day Baltic Sea. The ‘Ferraz-type’ shell beds of the Paraná Basin represent genetically complex and highly heterogeneous sources of paleontological data. They are cumulative records of spectra of benthic ecosystems time-averaged over long periods of time (10²–10⁴ years judging from actualistic research). Detailed biostratinomic reconstructions of shell beds can not only offer useful insights into their depositional histories, but may also allow paleoecologists to optimize their sampling designs, and consequently, refine paleoecological and paleoenvironmental interpretations.     

Paleoenvironment of Ankilitelo Cave (late Holocene, southwestern Madagascar): implications for the extinction of giant lemurs

Following human arrival, Madagascar suffered well-documented megafaunal extinctions and widespread deforestation. Although humans are widely considered to be the primary cause of the extinctions, the relative contributions of climate change and human activities to this ecological transformation remain uncertain. Reconstructing the habitats of the giant lemurs of Madagascar can provide key information for understanding the evolutionary mechanisms involved in their extinction. In this study, I present a faunal analysis of the subfossil assemblage from Ankilitelo Cave, southwestern Madagascar. This assemblage documents the latest known occurrence of five species of extinct giant lemur, in association with abundant well-preserved small mammal remains. I compared the small mammal fauna at Ankilitelo with 27 extant Malagasy mammal communities spanning the range of Madagascar's habitat types. Similarities in species composition between modern communities and Ankilitelo were assessed using cluster analysis. Ecological similarities were examined by assigning each species to dietary, locomotor, activity pattern, and body size categories. Multiple discriminant analysis was then used to classify Ankilitelo relative to modern habitat types in Madagascar, based on the ecological structure of the subfossil fauna. Results indicate that the habitat surrounding Ankilitelo during the late Holocene was similar to the succulent woodlands of modern southwestern Madagascar. This suggests that approximately 500 yr BP, these semi-arid habitats supported a subfossil lemur community that included the highly-suspensory Palaeopropithecus, and deliberate slow-climber Megaladapis, as well as Archaeolemur, Pachylemur, and Daubentonia robusta. In such environments, these giant lemurs would likely have been highly vulnerable to increasing human pressure in southwestern Madagascar.     

The late Maastrichtian nannofossil record of climate change in the South Atlantic DSDP Hole 525A

The phytoplankton response (calcareous nannofossils) to the Late Maastrichtian climate evolution is investigated in the South Atlantic DSDP Hole 525A and compared to published geochemical and micropaleontological data. The results point to a succession of dramatic climatic fluctuations. “Cool-water indicators” (Ahmuellerella octoradiata, Kamptnerius magnificus and Nephrolithus frequens) suggest cool surface water conditions prevailed during Chron C30n. At the top of C30n, their sudden drop in abundance, the last occurrence of B. constans and the concomitant increase in the tropical species Micula murus suggest warming and lower surface water productivity. An M. murus acme within Chron C29r reflects maximum warming. During the last 100 kyr of the Maastrichtian, the decrease in M. murus and increase in cool-water indicators reflect rapid cooling with the cool climate persisting over. The calcareous nannoplankton response to climate change correlate with similar findings in the Equatorial Atlantic Hole 1258A and parallels the stable isotope record of planktic and benthic foraminifera of DSDP Hole 525A as well as the decline in ¹⁸⁷Os/¹⁸⁸Os. Comparison of this marine record and the continental climate record in North America suggests a link between Deccan volcanism and the late Maastrichtian warm event.     

Biofaciès à Cuneigervillia-Pteromya et biofaciès à Eomiodon dans l'Hettangien du Quercy (Aquitaine orientale)

New research made in the Hettangian sequence in Quercy by one of us (R.C.) has led to the discovery of shell beds constituted solely of Bivalvia in two deposits in the departement of Tarn, one near Vaour, the other near Les Cabannes-de-Cordes. These Eomiodon and Cuneigervillia-Pteromya signify an environment of abnormal salinity and permit long distance correlations.