For many paleobiologists summer is that part of the year during which data is gathered in its purest form: fossils. Such summers may take you in diametrically opposite directions, though. Some bring broadly boasted outdoor adventures of fieldwork. Others, however, take you deeper and deeper into the collection labyrinths in the dark bowls of natural history museums around the globe. Despite what others may let you believe - and don’t tell anyone we told you - fieldwork is often boring, tedious work, the outcome of which - if any - is generally unknown. Sometimes long after you have made it back to the lab - as is the case for most palynological expeditions - you still have no clue if the trip was successful or not.
Digging deep in museum collections, on the other hand, can be surprisingly exciting. It is like treasure hunting with the guarantee of success. Now when you tour the big museums in the world, you’re bound to run into fellow hunters. Wherever you may go, you always run in to other members of our tiny community. They are like snowbirds that tour the same limited number of Arizonian RV parks in winter. This year we realized: we’ve joined this small herd of museum nomads. Our trip this summer to the Museum für Naturkunde in former East Berlin was no exception. On the first day of our visit Harvard’s Andy Knoll gave a talk, and we saw Scotsman and paleontologist Allistair McG striding the hallways, a sight we had seen before during our stay at the Smithsonian’s NMNH.
The species that brought us to Berlin is Pleuromeia sternbergii - a 250 million year old quillwort. P. sternbergii is one of the few plant species that actually thrived during the aftermath of the end-Permian crisis, the largest mass extinction ever recorded. From the moment we heard of the plant, we were intrigued by the incredible success of this paleobotanical oddball. Word has it that the first Pleuromeiawas discovered in the 1830s when - during a repair - a sandstone block fell from the Cathedral of Magdeburg and broke into pieces on the pavement (Mägdefrau, 1968). The accident revealed a piece of fossil Pleuromeia stem; nine years later first described by count Georg zu Münster as a Sigillaria species. Fortunately for us, the quarry that produced the stones that built the cathedral was known to be close to the nearby town of Bernburg. Many more important specimens have been found in the same quarry since, and that’s exactly what we were after in Berlin.
Typical Pleuromeia fossils look like a small baseball bat, often with a spirally arranged pattern of dimples on it. These are almost always sandstone casts (infillings) of decayed Pleuromeia stems. Since the decay of these lycopsid stems occurs in distinct phases - starting from the inside-outward, depending on the resilience of concentric tissue layers – virtually all remains are casts of inner stem tissues layers. Now among the many published papers on Pleuromeia sternbergii - the first ones starting in the late 1800s - there was one of by Mägdefrau (1931) that figured a rare feature: the detailed leaf scars on the outside of a Pleuromeia stem. This is crucial information for a new reconstruction we plan to make of P. sternbergii. However, for most of the 20th century this important specimen was considered lost, until someone recently rediscovered it in Berlin. So we had to see it.
While walking through the hallways of the 121 year old museum building, we stared in the face of a Brachiosaurus brancai, the largest mounted dinosaur skeleton (really, it's in the Guinness book of records), walked past a wooden closet decorated with Paleozoic sea lilies and fossil horsetails in wood carvings, and saw many nice old paleo reconstructions. A stone staircase led the way to the attic of the museum; that’s where the Mesozoic paleobotany collections are housed. The collections space is not air conditioned, and it was around 100 degrees Fahrenheit outside. Up on the attic it was quite a bit warmer, so we had to take care not to spill little streams of sweat on the fossils. Luckily, a small table fan was already performing its duty. We sat down and started browsing though three cabinets with Buntsandstein collections.
Mesozoic plant curator Barbara Mohr very modestly apologized that the collection was not very extensive, but we couldn’t believe our eyes. They turned out to have a huge number of specimens, most of which were collected in the 19th century. Many of the specimens showed important features that have never been published on. Beside the unique specimen with detailed features of the outside of the stem, we found three more specimens. There was a lot of reproductive material in the collection as well - terminal cones, isolated sporophyls and dime to quarter-sized sporangia. Moreover, a short stack of drawers contained hundreds leaf fragments. Now leaves have hardly been figured in Pleuromeia publications, so that was something we knew very little about. For two days, we felt like two little kids in a candy store, photographing as much as possible.
Ceci n’est pas une Pleuromeia
Overseeing this enormous collection, we realized how far off we were with our earlier whole-plant reconstruction of Pleuromeia (see fig.). Now we need to get started on a new one a.s.a.p. Of course, each illustrated reconstruction of an extinct organism or landscape is a hypothesis, and should be treated as such. However, such graphic hypotheses seem almost immune to the natural selection of other memes such as more conceptual, verbal hypotheses. That is because most ‘users’ are not so much interested in the intellectual merit of the hypothesis, but are looking for a pretty picture of an old dead thing. Therefore, falsified but pretty reconstructions have a very slow decay rate, or may even grow in importance. Thus, falsifiability - the one thing that sets scientific claims apart from most non-scientific ones - is continuously threatened by esthetics... The fact that in most reconstructions it is impossible to see the degree of accuracy of the various depicted components adds to the problem. In an ideal world all reconstructions come with an integrated disclaimer or are all just really ugly. Until then, we’d better make sure that each new reconstruction looks better than the predecessor it replaces.
Karl Mägdefrau 1934. Zur Morphologie und phylogenetischen Bedeutung der fossilen Pflanzengattung Pleuromeia. Beih. Bot. Centralbl. 48: 119-140.
Karl Mägdefrau 1968. Paläobiologie der Pflanzen. 4th edition, Fischer, Stuttgart, 549 pp.