Fieldwork Photo of the Week

See the spy in the back? Some Kyrgyz aborigines can't help being distrustful...

I'm thankful to Juliane Hentschke who safed us these moments and a number of bones.

Tectonics & Paleo (4):The world of CPOs and ODFs

Materials in geoscience and biology are often not isotropic - their properties, such as conductivity, soundwave velocity, and shear strength, vary with direction.

The reason can be that they are crystalline - if so, the orientation of the crystal lettice of (one, a few, or) many individual crystal grains has an influence on the properties of the compound material. The individual crystal lettice orientations can be at random or their can be a preferred orientation.

A whole branch of mineralogy and material science deals with the analysis of materials which show crystal preferred orientations (CPOs).

From Tectonics...

Structural geologists, who are dealing with microscopic phenomena of tectonic deformation, use mineral textures of rocks, i.e. crystal preferred orientations of the rockforming minerals, as indicators of tectonic movement and deformational regimes (temperature, pressure conditions; deformation rate).

The so-called Orientation Distribution Density Function (ODF) describes how the crystal axes of mineral grains in a sample are oriented relative to an outer coordinate system (e.g. geographic XYZ coordinates). From the ODF, usely depicted as a couple of stereographic density plots (e.g. plots for the crystal a-axis, b-axis and c-axis orientations) the direction and sense of shearing of a rock can be inferred.

...to Paleontology

Not only tectonic forces are governing the crystalline properties of natural materials. In a similiar way the (often monomineralic) mineralized tissues of organisms are underlying specific biological formation conditions - the different layers of a skeleton can show rather perfect CPOs.

Crystal orientations in mineralized tissue are, of course, not defined relative to a geographic coordinate system but to the anatomic directions (or the axis of accretionary growth) of the animal as a reference system.

Coming from the tectonical side I was participating in a workshop on "Textures & Microstructures in Geosciences" in 2005: I was really surprised that there is an application of texture analysis in palaeontology and that some people are really doing it.

Methodology

You can do either single grain measurements or methods integrating all orientations of crystal grains in a certain volume of the sample.

U-stage and EBSD are involving single grain measurements of a thin section: For each grain in a certain raster the individual crystal orientation is determined - either by its optical properties using the universal stage (this old-fashioned manual method is rather time-consuming) or by the way how electrons from an electron microbeam are backscattered on a detection screen (Electron Backscatter Diffraction, EBSD). The detected Kikuchi line patterns are indicative for how an individual crystal is oriented (they can be interpreted automatically). What you get in both approaches is not only an ODF but also a crystal orientation map of your thin section.

XRD, Neutron Diffraction. In these methods an X-ray or neutron beam is used to measure a larger volume of a sample comprising several crystals, thereby neutron radiation can penetrate even larger samples completely while the X-ray has a relatively low depth of penetration. From the detected line sprectra pole figures, representing the distributions of certain crystal lettice plane orientations can be derived (from which in turn the ODF of all the crystals in the measured sample volume can be deduced).

Examples from Paleontology

Chateigner, D., Hedegaard, C. & Wenk, H.-R. (2000): Mollusc shell microstructures and crystallographic textures. - Journal of Structural Geology 22: 1723-1735.

The authors employ X-ray diffraction measurements and demonstrate thate the microstructures and crystallographic textures of aragonite layers of species from different mollusc taxa including bivalves, cephalopods, gastropods and monoplacophorans are highly specific and contain a phylogenetic signal: closer relatives are more similar in their shell's crystal orientations.

Pyzalla, A.R., Sander, P.M., Hansen, A., Ferreyo, R., Yi, S.-B., Stempniewicz, M. & Brokmeier, H.-G. (2006): Texture analysis of Sauropod bones from Tendaguru. - Material Science and Engineering A 437: 2-9.

This neutron diffraction approach addresses the question whether the apatite crystallite textures in adolescent and adult Brachiosaurus long bones show some signal indicative for specialized crystal orientations which can be attributed to the giant growth of sauropod dinosaurs. However, comparing their results to the measurements of turkey and other dinosaur long bones they found no significant difference in texture strength or in the predominant direction of fibres.

Prospects

Given the elaborateness of most approaches, measurements of crystallographic textures are rarely used in paleontology - I suppose this will change if it turns out that the analysis of the crystal orientations can provide substantial information which is not obtained from the usual analysis of skeletal histology and microstructures.

Happy Darwin Year!

Coming to us in 2009: festivities and colloquia celebrating the 200th birthday of Charles Darwin and the 150th anniversary of his grand oeuvre

On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life,

which was "introducing sense into biology" (badly corrupted from the Ernst Mayr quote).

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Looking back a palaeoherpetologist would call 2008 the year of the turtle:

With the descriptions of Odontochelys and Chinlechelys and some further contributions (a list is provided by N. Gardner) the origins of turtles were greatly enlightened.

This topic was variously covered by the pal(a)eo and evo blogs – see for example here and here (Bill Parker's Chinleana) or here and here (Adam Yates' Dracovenator blog).

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BTW: How many recent On-papers do you know?

What is the right occasion to start a contribution with 'on'? Did you ever think about it ... to me such a beginning suggests a long-winded reflection of/ a comment on sth. rather than focusing on the presentation of new data.

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The Twelve Days of (Paleo) Christmas are not yet over - you are still welcome to participate in the poll. >>>>>

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I support Scientific Triassicism! An initiative by Neil from Microecos. What do you think: Is 'Triassic Science' or 'Triassology' a sexier term?

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(How long one week and a half can be: I forgot how to compose a text, that's why this post is only a list of notes.)

Fieldwork Photo of the Week

Excursion group 2008 and Madygen badlands, close to the boundary between "Variegated Member" (T3) and "Upper Graycolored Member" (T4) of the Madygen Formation (subdivision of Dobruskina 1995).
The transitional zone includes sandstone horizons with large-scale x beds.

Madygen: Recent contributions to symposia

12th International Palynological Congress, Bonn 2008:

Philippe Moisan, Hans Kerp, Sebastian Voigt, Benjamin Bomfleur: The fossil flora of the Madygen Formation from the Middle to Upper Triassic, Kyrgyzstan, Central Asia. Terra Nostra 2008/2: 194

Abstract. The Middle to Late Triassic Madygen Formation (Kyrgyzstan, Central Asia) is a unique fossil lagerstaette for Early Mesozoic insect remains and small reptiles with soft-tissue preservation. Plant fossils from these deposits from are known since the 1930s and constitute one of the richest and most diverse Triassic floras of Eurasia. However, they received very little attention to date and their studies have to date been based on macromorphological features only. We present the first record of epidermal features of this diverse Triassic flora based on recently recovered fossil plant material. Many of the Madygen plant fossils show a highly remarkable preservation. Due to its very fine grain-size, the embedding sediment has often formed a natural cast of the epidermal cell pattern. Such epidermal features allow detailed systematic descriptions as well as palaeoecological interpretations. This fossil flora is dominated by pteridosperms, ginkgophytes, and sphenophytes. In addition, algae, mosses, lycophytes and ferns occur and many are new for this fossil flora. The high abundance of fructifications is of particular interest. Another important aspect of the Madygen flora is that many gymnosperm leaves show evidence for plant-insect interactions (e.g. margin feeding, oviposition, mining traces). The supposed Middle to Late Triassic age of the flora coincides with one of the most important herbivore expansions in the fossil record. However, while this phenomenon has been recognised in the Middle and Upper Triassic of the USA, Western Europe, and South Africa, no data are available from coeval Central Asian sequences. The on-going study aims to provide a revised systematic description of the plants, including epidermal features to characterise the palaeoecosystem of the Madygen lagerstaette in more detail, and to contribute to a better understanding of the evolution of plant-animal interactions during the Early Mesozoic.

Ichnia, Cracow 2008:

Voigt, S., Buchwitz, M.: On the Mermia ichnofacies in a Triassic overfilled lake-basin of Southern Fergana (Kyrgyzstan, Central Asia). Ichnia 2008, Cracow (Poland), September 1- 5

Abstract. Fluvio-lacustrine deposits of the Madygen Formation on the northern rim of the Turkestan Mountains in southwestern Kyrgyzstan are one of the few occurrences of Triassic continental strata in Central Asia. During the 1960s Russian palaeobiologists successfully explored the stratum typicum area of the Madygen Formation for macrofossils, unearthing a remarkably rich Early Mesozoic flora, thousands of insect remains, and unusual reptiles with soft-tissue preservation (Dobruskina, 1995). Considering the number, diversity and preservation of the finds, the locality represents a lagerstaette. Lacking investigations on the geological and palaeoecological background of the findings, however, its particular importance for the evolution of terrestrial ecosystems has not yet been revealed. Thus, a comprehensive approach on the Madygen ecosystem including a detailed facial analysis of the fossil-bearing strata is currently carried out.
The Madygen Formation is an up to 500 m thick series of predominantly siliciclastic rocks, which formed in an intermontane basin under humid to semi-humid climatic conditions. Sedimentary successions are composed of alluvial fan conglomerates, channel sandstones and overbank fines with intercalated coal seams of a highly-vegetated alluvial plain, as well as deltaic sandstones and laminated lacustrine mudstones of basin centre. Shallowing upward sequences and various other features, e.g. dense vegetation, wet soils, and the lack of desiccation cracks, typify the depositional environment of the Madygen Formation as an overfilled lake-basin sensu Bohacs et al. (2000).
Though they were never mentioned in earlier palaeontological reports, trace fossils of the Mermia ichnofacies belong to the most common phenomena of the Madygen fossil assemblage. Networks of tiny, irregularly branched burrows with high bedding-parallel extension are ubiquitous in the laminated mudstones of the lake deposits. Architecture and size of the burrows indicate deposit-feeding, worm-like trace makers such as the extant oligochaetes and aquatic insect larvae. The bioturbation maximum is recorded in mudstones of the transitional sublittoral to profundal lake zone which probably included a chemocline as in some modern stratified lakes. More shallow but clearly submerged parts of the lake were occupied by benthic ostracods and kazacharthra - triopsid-like branchiopods which are thought to be endemic to the Mesozoic of Central Asia (Chen et al., 1996). Body imprints of the kazacharthra occur spatially close to ribbon- and sickle-shaped trace fossils. We are attributing these traces to different types of kazachartran feeding activity: (1) grazing if the ground water layer is well aerated and (2) short-term mud-diving under oxygen-depleted conditions. All ichnia – the shallow penetrative traces and the presumable kazacharthran traces – were produced in the permanently subaquatic environment of a sizeable lake with a minimum length of 1.7 km. The restriction of trace types to a certain ground level relative to the chemocline may yield a basic approach for the subdivision of the Mermia ichnofacies.

German Paleontological Society Meeting, Erlangen 2008:

Voigt, S., Buchwitz, M., Fischer, J., Krause, D.: Longisquama's dorsal skin appendages: new finds from the type locality. Erlanger Geologische Abhandlungen, Sonderband 6: 117

Abstract. During the 1960s Russian palaeobiologists discovered two incomplete diapsid skeletons with skin impressions in lacustrine shales of the Triassic Madygen Formation, a continental sedimentary succession in southwest Kyrgyzstan, Central Asia. Described by A.G. Sharov in 1970 and 1971 the two finds became known for the uniqueness of the species they represent: While Sharovipteryx mirabilis was an early limb-supported reptilian glider with an exceptionally large uropatagium and probably an archosauromorph, Longisquama insignis, whose systematic position is still controversial, displays a series of elongate hockey-stick-shaped skin projections, rooting along the dorsal midline of the body. The appendages are structurally complex and some morphological features, e.g. the presence of a middle axis and the assumed branching, have motivated their comparison with avian feathers. Apart from four Longisquama paratype specimens with isolated skin appendages no further material belonging to one of the two diapsid species has ever been documented.
Here we report three new finds of the Longisquama appendages which have been recovered from the type locality in the northwestern Madygen outcrop area (Urochishche Dzhaylyau-Cho) during fieldwork in 2007: The single exemplar FG 596/V/1 has a length of 28.9 cm, exceeding all other known specimens by at least 100%. Comparable to the appendages of the holotype it comprises a narrow and relatively long proximal section with a tripartite appearance and a relatively short and wide distal section whose two corrugated longitudinal lobes are separated by a prominent middle axis. The apical end and the basal end are not preserved. FG 596/V/2 and FG 596/V/3 represent 3.6 and 3.7 cm long fragments of the distal section. In FG 596/V/1 and FG 596/V/3 the imprints on the left slab and right slab enclose a thin continuous sedimentary core, a feature which has been regarded as indicative for the overall membranous constitution of the appendages.
Especially the very long specimen FG 596/V/1 has some importance for the developmental and functional interpretation of Longisquama’s skin structures: Exceeding the proximal width of other dorsal appendages by only a small amount its length/ basal width ratio is conspicuously high (>50). This can be interpreted as a consequence of uniaxial growth with the constricted proximal and the extended distal section representing two distinct phases of a developmental cycle. Considering the shape and dimensions of FG 596/V/1 we find no easy explanation how the appendages could have formed a closed and stable airfoil, let alone one which produces enough lift to support gliding flight as assumed by the exponents of the hypothesis of a two-wing airborne Longisquama.

Buchwitz, M., Voigt S.: Dermal plates of a Triassic chroniosuchian with unique articulation mechanism. Erlanger Geologische Abhandlungen, Sonderband 6: 24