Chroniosuchians and stay in Moscow

To resolve the riddle: The bonified eyeball from the last post represents a a ball-shaped intercentrum of a chroniosuchid from the Permian of Russia.

In chroniosuchian reptiliomorphs the intercentra (white arrows) are interlocked with the amphicoelous pleurocentra in a ball-and-socket-like fashion. The image on the left shows some section of a Chroniosuchus vertebral column in ventral view. Intercentra become bony balls only in the adult individuals - not fully bonified in sub-adults and juveniles they are preserved with a crescent, disk-like or ellipsoidal shape.

Also, the fusion of the neural arch with the pleurocentrum - a feature otherwise characteristic for "higher reptiliomorphs" such as seymouriamorphs and diadectomorphs - is only completed in the course of ontogenesis (so that you can find suture lines in the subadult individuals).

Moscow: Paleontological Institute and Museum of the Russian Academy of Sciences (PIN)

The paleo-style PIN building has a castle-like rectangular shape with an inner courtyard featuring life-size sculptures of fossil critters from Russia and areas of the former Soviet Union. The exhibition has almost everything you wish for as a vertebrate enthusiast (here depicted: the two-story dinosaur hall). Rich in type specimens the collection is essential for some and important for many studies - so earlier or later many of the fossil vertebrate people spend some time there.

Concering the Chroniosuchia: With the exception of bystrowianid chroniosuchian remains from Kupferzell, Germany (Witzmann et al. 2008) and China (Young 1979) and some rather questionable Chinese chroniosuchid chroniosuchians (Li & Cheng 1999), all yet described Permian and Triassic chroniosuchian taxa come from the European part of Russia and are mostly archived in the PIN. I am thankful to Valery Golubev who helped me a lot during my week of stay when I was studying the type materials and to Jury Gubin who nicely put up with me in his room.

Some literature on chroniosuchians

Here considered: titles also available in English (plus the Chinese ones mentioned above).

Golubev, V. K. (1998). "Narrow-armored Chroniosuchians (Amphibia, Anthracosauromorpha) from the Late Permian of Eastern Europe." Paleontologicheskij Zhurnal 1998(3): 64- 73. [Russian, English]

Golubev, V. K. (1998). "Revision of the Late Permian chroniosuchians (Amphibia, Anthracosauromorpha) from Eastern Europe." Paleontologicheskij Zhurnal 1998(4): 68- 77. [Russian, English]

Golubev, V. K. (1999). "A new narrow-armored chroniosuchian (Amphibia, Anthracosauromorpha) from the Late Permian of the East Europe." Paleontologicheskij Zhurnal 1999(2): 43- 50. [Russian, English]

Li, J., Cheng Z. (1999). " New anthracosaur and temnospondyl amphibians from Gansu, China." Vertebrata PalAsiatica 37(3): 234- 247. [Chinese with English abstract]

Novikov, I. V., M.A. Shishkin (2000). "Triassic chroniosuchians (Amphibia, Anthracosauromorpha) and the evolution of the trunk dermal ossifications in the bystrowianids." Paleontological Journal 34(supplement): S165- S178. [English]

Novikov, I. V., M.A. Shishkin, V.K. Golubev (2000). Permian and Triassic anthracosaurs from Eastern Europe. The Age of Dinosaurs in Russia and Mongolia. M. A. S. M.J. Benton, D.M. Unwin, E.N. Kurochkin. Cambridge, Cambridge University Press: 60- 70. [English]

Witzmann, F., R.R. Schoch, M.W. Maisch (2008). "A relic basal tetrapod from the Middle Triassic of Germany." Naturwissenschaften 95(1): 67- 72. [English]

Young, C. C. (1979). "A new Late Permian fauna from Jiyuan, Honan." Vertebrata Palasiatica 17: 99- 113. [Chinese with English abstract]

Bonified eyeball

Or what the hell is this?

Lineage concept vs cladistics in continental biostratigraphy

The white hair of my chief Ph.D. supervisor is to some degree explained by his livelong efforts to get a grip on Carboniferous to Permian continental biostratigraphy - trying out different groups such as cockcroaches, conchostracans, freshwater sharks, and amphibians.

One of the underlying concepts which I suppose I will always find hard to believe is the idea of searching for and finding so-called lineages, i.e. series of species occurring subsequently in the stratigraphic record which show stepwisely distinct anatomies because each species has descended from the respective next-oldest species.

Of course every species has an ancestor and many have descendants but how can I define them from the fossil record? Is there not the typical problem of epistemic vagueness of the ancestor in any kind of phylogeny (e.g. discussed by Wolf-Ernst Reif in some of his many theoretical papers on cladistics in paleontology)?

Searching for lineages leads to a fallacy?

The idea that whithin a continental sedimentary succession a certain species occurring deeper than a related species should be regarded as the ancestor of the latter - unless disproven - always reminded of a type of logical fallacy called post hoc ergo procter hoc: "B occurred later than A, therefore A must be the reason for B." In terms of imposing the lineage concept: "Species B occurred subsequent to species A, therefore A must be the ancestor of B."

If a multiple- and irregularly branched bush is a good analogon to how evolution works I daresay the idea of a biostratigrapher to pick up the isolated fragements of branches (i.e. fossils) and glue them together in a few long continuous branches results in a bad model of the bush.

The problems occur after I have established a biostratigraphic zonation concept on the basis of what I think is a lineage: Someone working on the same material puts the species of my 'lineage' into a cladistic analysis and finds that there is almost no concordance between the appearance date of a species and its likely phylogenetic position.

If I do agree that similarities/ dissimilarities in morphology, histology, behavior, etc. should form the basis of a classification and consider the data basis of the phylogenetic analysis as sufficient I will have to admit that my scheme has been proven wrong. Or else if I suppose that the data are not sufficient and I myself cannot add more then I will have to concede that my scheme is at least no more valid than the alternative.

Proving microevolution depends on the sufficiency of "population" samples?

Im not saying that it is impossible to find arguments in favor of an ancestor-descendant relationship: Imagine I have large enough sample of specimens of the supposedly related species A, B, and C from three successive horizons. For A, B, C the empiric distributions of morphological parameters can be compared:
If the mean value & variance for A is not signficantly distinct from the mean and variance of B and
if the mean value & variance for B is not signficantly distinct from the mean and variance of C
but given a significant difference in the mean values/ variances of A and C,
I could infer that from A to C microevolution took place...
...but do we have such samples, let's say for tetrapods?

An example: Amphibian Biostratigraphy

These problems have been discussed for the amphibian biostratigraphy of the European Permocarboniferous as developed by Werneburg and Schneider and applied for various amphibian occurrences, see for example:

R. Werneburg & J.W. Schneider, 2006, Amphibian biostratigraphy of the European Permo-Carboniferous. In: S.G. Lucas, G. Cassinis and J.W. Schneider, Editors, Non-Marine Permian Biostratigraphy and Biochronology: Geological Society of London, Special Publications 265 (2006), pp. 201–215. [Link]

R. Werneburg, A. Ronchi, and J.W. Schneider, 2007, The Early Permian Branchiosaurids (Amphibia) of Sardinia (Italy): Systematic Palaeontology, Palaeoecology, Biostratigraphy and Palaeobiogeographic Problems. Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 252, Issues 3-4, 3 September 2007, Pages 383-404 [Link]

The zonation scheme and proposed lineages have been criticized by Steyer (2004) as being a stratophenetic rather than a true phylogenetic approach considering the criteria how the authors relate different species:

J. S. Steyer, 2004, Phylogenetic or stratophenetic systematics? - Comment of R. Werneburg: The branchiosaurid amphibians from the Lower Permian of Buxières-les-Mines, Bourbon l’Archambault Basin (Allier, France) and their biostratigraphic significance. Bull. Soc. géol. France, 2004, 175 (4), 423-425
[Link]

Another particular problem is that amphibians are known to be abundantly subject to heterochronous evolution - evolutionary shifts in the ontogenesis, in particular, neoteny, is a common phenomen and can obscure characteristic features.

A recent analysis by Schoch & Milner (2008) on branchiosaurids, a group of neotenic small dissorophoid temnospondylians which is often considered for biostratigraphy, features a cladistic approach and proposes a scenario, related to which nodes of the tree neoteny/ life style changes occurred:

R.R. Schoch & A.R. Milner, 2008, The intrarelationships and evolutionary history of the temnospondyl family Branchiosauridae. Journal of Systematic Palaeontology (2008), 6 : 409-431 [link]

While the relationship of Branchiosaurus forming the outgroup of major clades (Melanerpeton-clade, Apateon-clade) is correspondent to the order of occurrences in the stratigraphic record, certain long ghost lineages occur - in particular the interpretation of Apateon gracilis/Melanerpeton gracile shows a mismatch between the cladistic approach of Schoch & Milner and the scheme of Werneburg & Schneider. This divergence is also the consequence of conflicting interpretations of the gracil(e/is) material, however, it demonstrates the potential for stratigraphic misinterpretation:

If I believe that a species forms the end member of a lineage because it is the youngest in certain sedimentary sequences I may underestimate the species' stratigraphic range - unlike the cladistic analysis which (if well-founded) would imply a deep divergence suggesting that some of the earlier record of the species is missing.

Decoupling (continental) biostratigraphic zonation from the lineage concept

Assuming that evolution works rather bush-like than lineage-like, I dont' see why we can't keep a biostratigraphic zonation even in the case of sparse continental records. I still can associate a series of morphologically defined taxa with a certain stratigraphic range and spatial distribution - until the concept has been shown not to be adequate (or not outside a more narrowly defined spatiotemporal window).

Whether it is a lineage-like relationship of species or another factor (related to geography, climate, ecology or else) that makes biostratigraphy work is a question which might be solved only in some cases.

The Paleontologist

a children's song (Melody from "Der Volkspolizist")

1. My mom uses often so difficult words
But he tells me beast names that are so much worse:

The pa-leon-to-lo-gist
New names he invents
For fossil creatures
‘Cos he is our friend.

2. My toys are so harmless, my sister not fears –
He models a T. rex that drives her to tears:

The pa-leon-to-lo-gist
Revives an old land
With hard-plastic dinos
‘Cos he is our friend.

3. When dad says that he cannot fully explain
Why some critters die out while other do change.

The pa-leon-to-lo-gist
Has knowledge at hand
He gives us the answer
‘Cos he is our friend.

4. And when I’m a grownup I will find my bliss
Becoming the best pa-le-on-to-lo-gist.

Will unearth the dinos
Will brushup the bones
As witty but cooler
Than Indiana Jones.

PALHERP Bonn 2009

The Meeting of the German Paleoherpetologists was launched in 1997 as an act of rebellion against the old mammal establishment which ruled the regular vertebrate workshops of the German Paleontological Society. A particular aspect of the Palherp is the relaxed atmosphere giving students the chance to present ideas and results without unfair senior criticism.

Last weekend the 13th Palherp meeting was held in Bonn. As the Steinmann Institute of Bonn University houses the German Research Foundation Unit on Sauropod Biology you can call it one of centres of paleoherpetology in Germany. Given the focus of the Bonn working group many of this year's presentations covered dinosaurs and/or bone histology.

Saturday: Martin Sander's keynote lecture on sauropod biology was followed by presentations on sauropodlet longbone histology, on rib histology and sauropod reproduction strategies.

The lower tetrapod session covered chroniosuchians, a pelycosaur jaw fragment as the earliest German amniote find, parareptiles and a basal diapsid.

In the afternoon a presentation on didactyle theropod footprints from the Oberkirchen Sandstone and a discussion of arguments/ phylogenetic analyses in favour of convergent flight origins in the Eumaniraptora followed. Furthermore a talk on finds from the Lower Muschelkalk of Winterwijk. H. Haubold discussed problems related to the continental P/T mass extinction event if it is taken as a dogma.

Sunday talks included the introduction of a new basal sauropod (from Niger), dinosaur palaeopathology, tooth morphology, isotope palaeontology, and 19th century history of dinosaur science.