The Use of Fossil Caddisfly Assemblages in the Reconstruction of Flow Environments from Floodplain Paleochannels of the River Trent, England

This paper examines the use of fossil larval trichopteran communities to investigate and describe the flow environment of a paleochannel network in the middle reaches of the River Trent floodplain (UK). Previous research utilising fossil insect communities (principally O. Coleoptera, O. Chironomidae) has focussed upon climate reconstruction. However, larval trichopteran communities (O. Trichoptera) also offer an aquatic signal, giving information regarding channel habitat structure and flow environments. The taxonomic diversity of each fossil community and the categorisation of each taxon into a known flow group, using the “LIFE” methodology, facilitates the reconstruction of the river flow conditions at each site based upon known faunal associations with mean flow velocity. A total of 49 trichopteran taxa were recorded from 17 paleochannels (n = 170 samples). Detrended Correspondence Analysis (DCA) identified a environmental gradient on the first DCA axis that reflected variability in flow, from rapid/fast flow to slow flowing and standing water habitats. In addition, two distinct faunal groups were identified on the second DCA axis characteristic of (i) small nutrient rich lentic habitats; and (ii) larger water bodies displaying features of both lentic, lotic and ephemeral habitats where marginal vegetation is abundant on a mineral substratum. The results demonstrate that larval Trichoptera can be used in paleolimnological research to reconstruct a flow signal and provide additional information regarding the aquatic habitat structure. Their wider use in describing the aquatic environment, in association with other proxies (e.g., Chironomidae and Coleoptera), may provide a more holistic understanding of floodplain paleoenvironment succession.     

Paleoecology of Beringian “packrat” middens from central Yukon Territory, Canada

Rodent middens from ice-rich loess deposits are important new paleoenvironmental archives for Eastern Beringia. Plant macrofossils recovered from three middens associated with Dawson tephra (ca. 24,000 ¹⁴C yr B.P.) at two sites in Yukon Territory include diverse graminoids, forbs, and mosses. These data suggest substantial local scale floristic and habitat diversity in valley settings, including steppe-tundra on well-drained soils, moist streamside meadows, and hydric habitats. Fossil arctic ground squirrel burrows and nesting sites indicate that permafrost active layers were thicker during Pleistocene glacial periods than at present on north-facing slopes.     

An 8000-year record of vegetation, climate, and human disturbance from the Sierra de Apaneca, El Salvador

An ∼8000-cal-yr stratigraphic record of vegetation change from the Sierra de Apaneca, El Salvador, documents a mid-Holocene warm phase, followed by late Holocene cooling. Pollen evidence reveals that during the mid-Holocene (∼8000-5500 cal yr B.P.) lowland tropical plant taxa were growing at elevations ∼200-250 m higher than at present, suggesting conditions about 1.0°C warmer than those prevailing today. Cloud forest genera (Liquidambar, Juglans, Alnus, Ulmus) were also more abundant in the mid-Holocene, indicating greater cloud cover during the dry season. A gradual cooling and drying trend began by ∼5500 cal yr B.P., culminating in the modern forest composition by ∼3500 cal yr B.P. A rise in pollen from weedy plant taxa associated with agriculture occurred ∼5000 cal yr B.P., and pollen from Zea first appeared in the record at ∼4440 cal yr B.P. Human impacts on local vegetation remained high throughout the late Holocene, but decreased abruptly following the Tierra Blanca Joven (TBJ) eruption of Volcán Ilopango at ∼1520 cal yr B.P. The past 1500 years are marked by higher lake levels and periodic depositions of exogenous inorganic sediments, perhaps indicating increased climatic variability.     

Multivariate analysis of environmentally controlled variation in Lagena: Late Maastrichtian,Sweden

Costate forms of Lagena (benthonic foraminifer) have been studied in an uppermost Maastrichtian bore-hole core sequence (28 levels) from southern Sweden. Analysis of a large sample shows that consistent assignment to previously described “species” of costate Lagena is not possible. This observation is supported by multivariate analysis of five morphologic variables which indicates that there are no distinct clusters of specimens along principal component axes associated with general size, number of costae, and relationships between roundness of test/length and number of costae. Specimens with a basal ring differ from specimens with an apical spine and those with no basal structure with regard to average number of costae. They also differ from specimens with no basal structure with regard to relationships between roundness of test/length and number of costae. These characters grade into each other thus preventing them from being used as taxonomic criteria.Mean ratios of benthonic foraminifers to total benthonic and planktonic formaminifers determined individually for each level are inversely related to mean relative frequencies of costate Lagena and directly related to mean general sizes of costate Lagena. The benthonic/planktonic ratio has been suggested by other workers to represent a paleobathymetric index across a continental slope and shelf when open marine conditions prevailed. If this were so in the Danish basin at the end of the Cretaceous, costate Lagena would have been relatively less frequent and larger at shallower depths.As a result of the study, the analyzed specimens are considered as representing a single morphospecies of the costate species Lagena sulcata. Between-level variation is regarded as ecophenotypic, and within-level variation as natural biologic variation of no taxonomic significance. A total of about 1000 species of Lagena has been described in the literature which is probably many orders of magnitude too great for a genus with such a simple morphology as Lagena. A revision of the taxonomy of Lagena is, therefore, probably necessary on a wide scale.     

Aquatic adaptations in the four limbs of the snake-like reptile Tetrapodophis from the Lower Cretaceous of Brazil

The exquisite transitional fossil Tetrapodophis – described as a stem-snake with four small legs from the Lower Cretaceous of Brazil – has been widely considered a burrowing animal, consistent with recent studies arguing that snakes had fossorial ancestors. We reevaluate the ecomorphology of this important taxon using a multivariate morphometric analysis and a reexamination of the limb anatomy. Our analysis shows that the body proportions are unusual and similar to both burrowing and surface-active squamates. We also show that it exhibits striking and compelling features of limb anatomy, including enlarged first metapodials and reduced tarsal/carpal ossification – that conversely are highly suggestive of aquatic habits, and are found in marine squamates. The morphology and inferred ecology of Tetrapodophis therefore does not clearly favour fossorial over aquatic origins of snakes.     

Postglacial fire, vegetation, and climate history in the Clearwater Range, Northern Idaho, USA

The environmental history of the Northern Rocky Mountains was reconstructed using lake sediments from Burnt Knob Lake, Idaho, and comparing the results with those from other previously published sites in the region to understand how vegetation and fire regimes responded to large-scale climate changes during the Holocene. Vegetation reconstructions indicate parkland or alpine meadow at the end of the glacial period indicating cold-dry conditions. From 14,000 to 12,000 cal yr B.P., abundant Pinus pollen suggests warmer, moister conditions than the previous period. Most sites record the development of a forest with Pseudotsuga ca. 9500 cal yr B.P. indicating warm dry climate coincident with the summer insolation maximum. As the amplification of the seasonal cycle of insolation waned during the middle Holocene, Pseudotsuga was replaced by Pinus and Abies suggesting cool, moist conditions. The fire reconstructions show less synchroneity. In general, the sites west of the continental divide display a fire-frequency maximum around 12,000–8000 cal yr B.P., which coincides with the interval of high summer insolation and stronger-than-present subtropical high. The sites on the east side of the continental divide have the highest fire frequency ca. 6000–3500 cal yr B.P. and may be responding to a decrease in summer precipitation as monsoonal circulation weakened in the middle and late Holocene. This study demonstrated that the fire frequency of the last two decades does not exceed the historical range of variability in that periods of even higher-than-present fire frequency occurred in the past.     

Linderochelys rinconensis (Testudines: Pan-Chelidae) from the Upper Cretaceous of northern Patagonia: New insights from shell bone histology,morphology and diagenetic implications

The panchelid turtle Linderochelys rinconensis de la Fuente, Calvo and González Riga, 2007 was described on the basis of several postcranial elements from the Rio Neuquén Subgroup of Loma del Lindero site, near Rincon de los Sauces (Neuquén, Argentina). New preparation of the type material revealed new parts of the animal, including cervical vertebrae, parts of the carapace and a right tibia. The study of the newly recovered material herein improves our knowledge of the macroanatomy of this taxon. The first costal shows an axillary buttress similar to Australasian chelids and the cervical vertebrae morphology suggests a short-necked chelid condition. The re-examination of the type material of Linderochelys and the discovery of new material allowed new studies on microanatomy, osteohistology and diagenesis. Osteohistology suggests some similarities with Patagonian Cretaceous and Palaeocene Yaminuechelys, based on the presence of parallel-fibred bone in the external cortex and a much thinner internal cortex. Paleoecological studies on the proportions of forelimbs and microanatomy point towards aquatic or semi-aquatic habits, closely related to the condition seen in some extant South American chelids, such as Phrynops hilarii, Phrynops geoffroanus, and Mesoclemmys gibba. The fossil-diagenetic processes inferred substitution, fracturing, plastic deformation and permineralization events. Combined analyses through scanning electron microscopy with energy-dispersive X-ray spectrometry and petrographic studies revealed the substitution of hydroxyapatite by francolite. Permineralization stages include infilling of vascular canals, trabeculae and fractures with iron oxides and carbonate minerals during their burial history.     

Paleoecology of mangroves along the Sibun River, Belize

This study examines a sediment core (SR-63) from a mangrove ecosystem along the Sibun River in Belize, which is subject to both changes in sea-level and in the characteristics of the river's drainage basin. Radiocarbon dates from the core show a decreased sedimentation rate from ~ 6 ka to 1 cal ka BP and a marked change in lithology from primarily mangrove peat to fluvial-derived material at ~ 2.5 cal ka BP. Changes in the sedimentation rates observed in mangrove ecosystems offshore have previously been attributed to changes in relative sea-level and the rate of sea-level rise. Pollen analyses show a decreased abundance of Rhizophora (red mangrove) pollen and an increased abundance of Avicennia (black mangrove) pollen and non-mangrove pollen coeval with the decreased sedimentation rates. Elemental ratios ([N:C]_a) and stable isotope analyses (δ¹⁵N and δ¹³C) show that changes in the composition of the organic material are also coeval with the change in lithology. The decrease in sedimentation rate at the site of core SR-63 and at offshore sites supports the idea that regional changes in hydrology occurred during the Holocene in Belize, influencing both mainland and offshore mangrove ecosystems.     

Palynostratigraphy and paleobiogeography of the Jurassic – Lower Cretaceous succession in Kabrit-1 well,northeastern Egypt

Well-preserved and abundant Jurassic–Early Cretaceous palynomorph assemblages were recorded from the Kabrit-1 well, north Eastern Desert, Egypt. Thirty-one rock-cutting samples were analyzed and six rock units were differentiated. Seventy-one palynomorph species were identified from the productive samples. Six palynozones were differentiated, and they covered all the studied succession except for a palynomorph barren interval present in the uppermost part. These palynozones arranged in ascending order are as follows: two palynozones were recorded from the Middle-Upper Jurassic (Gonyaulacysta jurassica – Lithodinia jurassica Assemblage Zone and Klukisporites pseudoreticulatus- Systematophora penicillata – Escharisphaeridia pocockii Assemblage Zone) and the other four palynozones characterize the Lower Cretaceous deposits (Pilosisporites trichopapillosus – Cribroperidinium orthoceras Assemblage Zone; Dicheiropollis etruscus Interval Zone; Murospora florida – Afropollis operculatus Assemblage Zone and Afropollis jardinus Range Zone). We infer open marine conditions during deposition of the lower part of the Khalig El Ayoun Formation (Oxfordian-Kimmeridgian) and within the Kharita Formation (Albian), and shallow marine or coastal environments during deposition of the remainder of the studied succession. Paleobiogeographically, Late Jurassic index terrestrial palynomorph species documented here are in common with those previously recorded from North Africa, while marine dinocyst species are common to those documented from the West European and North American province. During the Early Cretaceous, the recorded terrestrial microfloral species were similar to those previously recorded from the West African-South American Province, while the marine dinocyst species were still related to the West European and North American marine palynofloral province.     

Detecting,sourcing, and age-dating dredged sediments on the open shelf,southern California,using dead mollusk shells

Molluscan shell debris is an under-exploited means of detecting, sourcing, and age-dating dredged sediments in open-shelf settings. Backscatter features on the Southern California shelf are suggestive of dredged sediment hauled from San Diego Bay but deposited significantly inshore of the EPA-designated ocean disposal site. We find that 36% of all identifiable bivalve shells > 2 mm (44% of shells > 4 mm) in sediment samples from this 'short dump' area are from species known to live exclusively in the Bay; such shells are absent at reference sites of comparable water depth, indicating that their presence in the short-dump area signals non-compliant disposal rather than natural offshore transport or sea level rise. These sediments lack the shells of species that invaded California bays in the 1970s, suggesting that disposal preceded federal regulations. This inexpensive, low-tech method, with its protocol for rejecting alternative hypotheses, will be easy to adapt in other settings.