Samstag, 10. September 2011

Madygen freshwater sharks made the JVP front page

Fischer, J., S. Voigt, J. W. Schneider, M. Buchwitz & S. Voigt (2011): A selachian freshwater fauna from the Triassic of Kyrgyzstan and its implication for Mesozoic shark nurseries. Journal of Vertebrate Paleontology 31: 937- 953. [Abstract]

Aha: Egg capsules and microvertebrate fossils can be a worthwile study object after all. (Event though Jan Fischer, my fellow grad student at the Geological Institute in Freiberg, had an interview with a critical local newsreporter who doubted that anybody could ever be interested in something like that.)

Jan and colleagues describe chondrichthyan egg capsule fossils from the Madygen Formation and refer them to Palaeoxyris, a capsule type usually assigned to hybodont sharks, and Fayolia, probably produced by xenacanth sharks. These fossils are accompagnied by nearby finds teeth of hybodont shark teeth - most of them are tiny and probably belonged to juveniles of the newly erected species Lonchidion ferganensis.

Oxygen isotope analysis of the teeth and their comparison to hybodont teeth from other localities yields a clear freshwater signal for the Madygen samples, indicating that the shark offspring indeed inhabited a freshwater habitat.

Facial analysis of the sedimentary succession of the Madygen Formation demonstrates the presence of wide-spread shallow and vegetated shore areas during the Middle Triassic which could have functioned as a shark nursery, i.e. a separate and ecologically distinct habitat for juveniles which was not invaded by adult sharks of the same species.

Dienstag, 10. Mai 2011

Triassic cicadomorph insects with camouflage

Shcherbakov, D. 2011. New and little-known families of Hemiptera Cicadomorpha from the Triassic of Central Asia – early analogs of treehoppers and planthoppers. Zootaxa 2836: 1-26. [article preview with abstract]

Dmitry Shcherbakov describes twelve new (monotypic) genera and species of cicadomorphs from the Madygen Formation on the basis of some exquisitely preserved fossils and redescribes three others.

He finds homoplastic similarities of the fossil families Saaloscytinidae and Maguviopseidae (newly erected) to leaf hoppers and tree hoppers (Membracoidea) and of Mesojabloniidae to plant hoppers (Fulgoroidea)

Convergent to the extant groups of cicadomorphs the newly described fossil taxa use different means of camouflage, namely bizarrely-shaped tegmina (singular 'tegmen' = anterior cover wings without aerodynamic function), dorsal projections on the thorax and tegmen, well-developed surface sculpture, and (dull) coloration. According to Shcherbakov the specific morphology of the Maguviopseidae and Saaloscytinidae mimicked thorns, bracts, seed-bearing organs, seeds, buds, or leaves, whereas the Mesojabloniidae mimicked rotten wood or bark.

Shcherbakov assumes that predation by tree-living reptiles, such as Sharovipteryx and Longisquama (which are known from the same locality within the Madygen Formation), was an important factor underlying the evolution of elaborate types of camouflage.

As none of these Triassic hoppers appear to have survived for long, Shcherbakov concludes that their extinction was linked to the extinction of the host plants whose plant organs they imitated.

Sonntag, 10. April 2011

A palaeodictyopteran and other relics from Madygen

Béthoux, O., S. Voigt, and J. W. Schneider. 2010. A Triassic palaeodictyopteran from Kyrgyzstan. Palaeodiversity 3: 9-13. [pdf 1.5 Mb]

Despite the substantial collection and study of insect fossils from the Madygen Formation (see overview in Shcherbakov 2008a) there are still unkown elements of the entomofauna left. Béthoux et al. (2010) describe a wing of a not yet reported group of insects from lacustrine shales of the northwestern ouctrop area of the Madygen Fm. (which also yielded Sharovipteryx and Longisquama).

Ruling out all alternatives on the basis of wing venation data, they come to the conclusion that reliquia spec. nov. was a late member of Palaeodictyoptera, an order-rank group according to conventional classification schemes that was previously thought to have died out during the Middle or Late Permian.

Béthoux et al. suggest that the disappearance of ancient insect groups in equatorial realms is linked to the Late Paleozoic aridisation in these areas that triggered the migration to wetter higher latitude ecosystems, such as the Madygen lake environment. The relatively late occurence of paleodictyopterans in Madygen is also in agreement with Shcherbakov's (2008b) hypothesis that the renewal of Triassic entomofaunas was asynchronous, starting in the lower latitudes and spreading to the higher latitudes.

Other Madygen relics?

Apart from modern groups, such as dipterans and hymenopterans among insects as wells as lissamphibians and archosaurs among tetrapods there are further relict forms, such as the choniosuchian Madygenerpeton or the basal cynodont Madysaurus. As hinted by Béthoux et al. the question to what degree and why Madygen functioned as a refugium is still to be answered.

Mittwoch, 30. März 2011

Chroniosuchia: Paper on osteoderm histology in online preview first experience with bone histology:

Buchwitz, M., Witzmann, F., Voigt, S. & Golubev, V. in press. Osteoderm microstructure indicates the presence of a crocodylian-like trunk bracing system in a group of armoured basal tetrapods. Acta Zoologica, DOI: 10.1111/j.1463-6395.2011.00502.x

Abstract. The microstructure of dorsal osteoderms referred to the chroniosuchid taxa Chroniosuchus, Chroniosaurus, Madygenerpeton and cf. Uralerpeton is compared to existing data on the bystrowianid chroniosuchian Bystrowiella and further tetrapods. Chroniosuchid osteoderms are marked by thin internal and relatively thick external cortices that consist of lowly vascularised parallel-fibred bone. They are structured by growth marks and, in case of Madygenerpeton, by lines of arrested growth. The cancellous middle region is marked by a high degree of remodelling and a primary bone matrix of parallel-fibred bone that may include domains of interwoven structural fibres. Whereas the convergence of Bystrowiella and chroniosuchid osteoderms is not confirmed by our observations, the internal cortex of the latter displays a significant peculiarity: It contains distinct bundles of shallowly dipping Sharpey’s fibres with a cranio- or caudoventral orientation. We interpret this feature as indicative for the attachment of epaxial muscles which spanned several vertebral segments between the medioventral surface of the osteoderms and the transversal processes of the thoracic vertebrae. This finding endorses the hypothesis that the chroniosuchid osteoderm series was part of a crocodylian-like trunk bracing system that supported terrestrial locomotion. According to the measured range of osteoderm bone compactness, some chroniosuchian species may have had a more aquatic lifestyle than others.

Freitag, 11. Februar 2011

Maths in Paleontology (I): Data

''In every special doctrine of nature only so much science proper can be found as there is mathematics in it.'' - Immanuel Kant, Metaphysical Foundations of Natural Science (1786)

Warningly the maths professor who got the unthankful task to teach us first-semester scientists-to-be some basic basics of his field chose Kant's statement as the first in his first lecture on "higher" maths. However, when I started my studies in geology and paleontology, there was another saying among old school geology teachers: "A bad mathematician makes a good geologist."

Many a fellow student were rather willing to believe in these latter words than in the inconvenient alternative. (I always considered this believe as outdated and I got the feeling that geology as a science might have been shaped not only by the talents of its protagonists but also by their limitations in terms of exactness and rigorousity.)

Luckily you were not necessarily considered as a bad geologist if you were interested in maths and the notion that modern geoscience involves maths and exact methods (e.g. methods of quantitative data analysis, databases, multivariate statistics and geostatistics, geoinformatics and geographic information systems, 3D and 4D modelling, remote sensing) was clearly on the rise. Perhaps from a biologists' point of view this story would be different, but, to tell you the truth, some of the biology-based paleontologists I got to know are not much living on the exact side either.

Apart from microscopy seminars, field, and lab practicals which teach you ways of data acquisition some classes in statistics and data analysis during first semesters of study give you an idea about the structure of data and ways how to sample and how to deal with data in order to find new knowledge, e.g. a relationship between two phenomena previously not considered to be related.

At the very beginning you will learn that there are different types of data used in paleontology and that you have to bring your data into shape for any kind of mathematical analysis tools, i.e. arrange them as a data table such as the following:

SpecimenClassState of XYZNo. of UVWsize L [mm]size M [cm²]

Normally lines of the table represent samples (or groups of samples or taxa) whereas columns may represent various features or measures. Such features may be the belonging to a certain class or category or the presence, absence, or specificity of a feature. Measured values as entries may have a discrete contribution (e.g. natural numbers such as the number of teeth or segments or body chambers) or a continuous distribution (e.g. length, area, angle, temperature measurements).

Various data relevant for paleontologists can be arranged as tables, such as morphological and microstructural data, stable isotope and other geochemical data, geographical, sedimentological, and stratigraphic data, as well as taphonomic and paleoecological data. Some of these data have a special structure and can be referred to one of the following types:

Compositional data...

... add up to 100%. Chemical compositions of fossils or faunal compositions are compositional data:

A23 [%]4217513

These data require careful considerations and a special kind of maths because all variables are (necessarily) correlated and thus an alleged dependence, e.g. of brachiopod and echinoderm abundances, can be obscured by variation in another group.

Spatially or temporally correlated data

‘Spatial correlation’ means that values for data points close to each other are more similar than values of more distant data points – e.g. the faunal composition of an ecosystem from Arizona is rather like that of a Nevada community than that of a Massachusetts community.

LocalityEasting (X)Northing (Y)FaciesArchosaurs [%]Rhynchosaurs [%]

Geostatistics is the usual method to deal with spatially correlated data. Spatial correlation can also occur on much smaller scales, e. g. the shape and size of two skull bones in contact to each other can show a stronger dependence than the shape and size of bones that are more distant to each other.

In paleontology temporal correlation is quite abundant, especially if your study considers different stratigraphic ages or sedimentological field data:

PopulationHorizonAr/Ar age [Ma]Faciesδ18O [‰]Average size [mm]
A1210 ± 1deltaic-2.05.2
B2aN/Adistal shelf1.46.4
C2c207 ± 2?2.16.8
D4200 ± 1deltaic-2.26.0

As in stockmarket analytics methods of time series analysis can be applied to interpret temporally correlated data (i.e. time series). Such data may be relevant for your study as they often indicate evolutionary trends (biological evolution in the stricter sense but also evolution of paleoenvironments), cyclic processes with a certain periodicity, and/or they can form the basis for relating contemporaneous processes in the geological past (e.g. stratigraphic correlation of separate sedimentary successions).

Orientation data

For elongated fossils such as conical shells or long bones the orientation of the fossil long axis towards the geographical cordinate system can be measured using a compass (with inclinometer). In a similar way the orientation of bedding planes can be documented. Such measurements are often used for the purpose of deducing the former transport direction of a ancient sediment transport and depostion system (such as a river, delta, or alluvial fan). A data table with orientation data may look like that:

Specimen No.DescriptionLength [cm]HorizonAzimuth>Dip
1long bone211N 20° E
2rib121N 10° W
3calamite stem802a N 15° E

“Azimuth” refers to the angle towards north. Orientation data are distributed on a halfsphere. Mean values (e.g. the average orientation of long bones) and other distribution parameters cannot be derived directly from the averaging of orientation angles but vector arithmetics has to be applied.

Cladistic data

Phylogeny on the basis of morphology conventionally involves cladistic methods, especially in the field of vertebrate paleontology which deals with a particular character-rich group that is deemed suitable for cladistic approaches employing certain kinds of analysis software specialized for the calculation of phylogenetic trees (e.g. PAUP, WinClada).

In cladistic datasets lines represent taxa, mostly species or genera of the group of interest, and columns represent characters (ordered by number), i. e. features of the skeleton which are variable among the included taxa:


One of the main issues in cladistics is the definition of characters and the correct (unbiased) coding of morphological information. You can include qualitative differences ("bone X contacts bone Y but not bone Z" = character state “0”; "bone X contacts bones Y and Z" = character state “1”) and quantitative differences ("length of metatarsal 3 larger than or as large as length of metatarsal 4" = character state "0"; "mt3 is shorter than mt4" = "1"). Sometimes mixed character states like "0 or 1 [but not 2]" occur in a taxon and are coded accordingly.

Missing data...

...occur all the time in paleontology ... either because specimens are not complete enough or because their geological age cannot be exactly determined or because specimens are too rare or valuable to use them for a destructive analysis method or because they are for some reason no longer accessible. "N/A" ("not applicable") or empty entries or question marks often symbolize missing data.

Some introductory literature:

Borradaile, G. J. 2003. Statistics of Earth Science Data. Springer, Berlin, 280 pages. ISBN 3540436030

Swan, A. R. H. and M. Sandilands. 1995. Introduction to geological data analysis. Blackwell, Oxford, 446 pages. ISBN 0632032243

Sonntag, 16. Januar 2011

New paper on cycadophytes from Madygen

Moisan, P., S. Voigt, C. Pott, M. Buchwitz, J. Schneider, and H. Kerp. in press. Cycadalean and bennettitalean foliage from the Triassic Madygen Lagerstätte (SW Kyrgyzstan, Central Asia). Review of Palaeobotany and Palynology. [DOI:10.1016/j.revpalbo.2010.11.008]

Philippe Moisan who is doing his Ph.D. in Münster (with paleobotanist Hans Kerp as his supervisor) studies the flora of the Triassic Madygen Fm. In his first paper on that issue he introduces cycadophyte finds collected between 2005 and 2009.

Many of the studied the specimen come from the same succession and locality as Madygenerpeton (there is also a small sketch of the sedimentary profile, see Fig. 2).

One thing I learned from this study was that so-called "xeromorphic features", i.e. plant features that are usually the consequence of an adaptation to aridity, cannot only occur in xerophytes, i.e. in plants adapted to dry environments, but (for other reasons) in hygrophytic and halophytic plants as well.

Indications for aridity, such as desiccation crack horizons or or seasonally drying-out ponds and rivers or wide-spread red bed sediments are lacking in Madygen. Thus, according to Philippe's interpretation, "xeromorphism" in Madygen plants probably served other purposes than the xeromorphism of xerophytes (e.g. "self-cleaning of the leaf surface, regulation of excessive radiation and leaf temperature, mechanical defense against phytophagous insects").