I told you we’d be stuck in that museum for a while. Here we go with a few samples of fossils from some of the layers in Holzmaden – it is interesting to note that the rocks that locally stand out as special units and got special names from the stone masons in many cases do not show up similarly in stratigraphic sections elsewhere. The Posidonia Shale may look uniform to laypeople, but experts can see quite some difference both within a local profile and between different localities. Let’s start at the top of the Holzmaden profile, with the base of the Lias ζ. The Jurensis-marls are light-coloured marls, which in some places follow on top of the Posidonia Shale with a seagrass horizon – the light-coloured marls fill crustacean-made burrows in the dark Lias ε. Elsewhere, there is a gap, which shows that erosion took place. The Lias Sea got shallow, and much better oxygenated at its bottom. As a direct consequence, the taphonomy changed, with fossils preserved in 3D, and soft tissues missing.
Acrocoelites tripartitus at the top is a belemnite, and if you wait for the next post the difference in preservation to the belemnites in the Lias ε will be immediately apparent. The ammonites are Lytoceras jurense (5a), Grammoceras radians (5b), Harpoceras striatum (5c) and Hammatoceras insigne. Compare them to the Dactylioceras commune on the rocks from the top-most Lias ε that they rest on!
I already posted some ammonites from the topmost layers in Holzmaden, the “Wilder Schiefer” or Lias ε III. Below it there are several fine shales and marly limestones, including the Lias ε II11, from which I can show you this beautiful ichthyosaur skull:
Directly below, the Flachen (Lias ε II10) is the last very regularly layered shale. From it come Pagiophyllum kurri, a conifer, and precious fish: Ptycholepis bollensis (3a) and Pholidophorus germanicus (3b).
The Wilder Stein (Lias ε II9) is again a more solid, carbonate-rich rock layer. Here, we finally get to see the namesake of the Posidonia Shale, the small bivalve Bositra buchi. If you now go “hu?” you’re in good company – the taxonomic history of the poor thing is almost as bad as that of Plateosaurus. it used to be called Posidonia, but no more. Here it is in the company of a beautifully coloured ammonite, Hildoceras subserpentinum.
Next up – or should I say next down? – is the Schieferklotz, Lias ε II6. FISHTIME!
Dapedium caelatum (bottom right), Pachycormus macropterus (top), Pachycormus curtus (bottom left) and Acidorhynchus brevirostris (tiny isolated skull). Fish….. well, fish. Wonder how they would have tasted fresh from the grill.
On we move, ever down…. a few centimeters under the Unterer Stein II5 this Lepidotus elvensis was found, a species that occurs only in this very narrow layer. The Untere Stein is rich in carbonate and accordingly the fossils are less deformed. However, you don’t want to have to prep them.
I’ll finish the “rock stair” in the next post. The new year will bring a real whopper of a fossil – promise!