Plateosaurus trossingensis and the Dino Mania in Württemberg

15.11.2023 | Prof. Dr. Rainer Schoch

The rich dinosaur site of Trossingen is a place of fascination and an annual site for excavations by the Stuttgart Natural History Museum. The latest findings and research methods provide information about these early giants, climate, vegetation and prehistoric local history.

The excavation site called "Rutschete" at the Obere Mühle near Trossingen (Picture: M. Rech / SMNS).

The "Rutschete"

When dinosaurs reached their enormous size in the Jurassic, Germany was covered by a warm shallow sea – the giant forms from this group of animals were, therefore, not native to our region. The dinosaurs early evolution, rapid rise, and the development of their diversity, on the other hand, are exceptionally well documented. One site in particular stands out: the "Rutschete" at the Obere Mühle near Trossingen. Discovered around 1908 by children playing, several very productive excavations were carried out on the 60 m wide and 12 m deep slope. The firm, violet-brown Knollenmergel unit contains numerous skeletons of the dinosaur Plateosaurus trossingensis, which could reach lengths of between 5 and 8 metres. These herbivorous dinosaurs are among the most common finds in this 205-million-year-old rock, deposited in an extensive clay mud plain.

New research methods reveal new secrets

The historical excavations by Eberhard Fraas (1911-13), Friedrich von Huene (1922-23) and Reinhold Seeman (1932) unearthed a total of around 80 skeletons in Trossingen, most of which are kept in the State Museum of Natural History in Stuttgart. There are also skeletons in Tübingen, New York and at Harvard University. Much has been learned from these findings: the anatomy of these early giants, their presumed locomotion and, most recently, their life history are hidden deep in the bones. Their age, growth rate and sexual maturity have become the subject of concrete research after decades of speculation. New methods such as bone histology and computer tomography have long allowed us to look deep into the microstructure of fossil bones, where veritable archives of biological data await decoding.

Turning point for Trossingen research

However, much is still unknown, so a doctoral thesis on the evolution of Plateosaurus using the example of the Trossingen finds is underway at the museum in cooperation with the University of Hohenheim. Over the last two years, Joep Schaeffer has examined the holotype - the scientific reference specimen with the number SMNS 13200 that is famous among experts – in great detail and is thus creating a new standard that will be a major turning point for future comparisons of dinosaur skeletons. The Knollenmergel in which the skeletons are preserved have also aroused the interest of our other palaeontologists: What do they say about the habitat of the plateosaurs, what did the landscape look like, and why did so many of them perish in Trossingen in particular? Our colleagues Dr. Eudald Mujal and Dr. Orla Bath Enright are investigating the formation of the different Fossil-lagerstätten of Baden-Württemberg, so evidently, Trossingen has also aroused their interest.

The deposit in Trossingen raises questions

Fossil-lagerstätten are fossil deposits that are usually regionally or locally exceptionally rich in fossils or contain remarkably well-preserved organic remains. Trossingen is a unique challenge in this research programme because the fossil deposit size is very unusual. After all, the finds at the site are not accumulated in layers a few centimetres thick, and the quality of preservation of the fossil bones is varied, with many bones criss-crossed by countless cracks. Some skeletons had already been lying around openly for years in the Triassic period, which partially weathered them. What is unique about Trossingen is the mass accumulation of skeletons in the tens of metres range, without it being possible to tell from the rock how far away the next skeleton is to be expected. A riddle to be solved, then.

If you don't give up, you will be rewarded!

When digging at the site, the monotony of crumbly, yet hard, and completely lithified clay can be very discouraging. Quite a few helpers who enthusiastically assisted in our digs did not return the following year. So, you need staying power, not to be frustrated by lulls and deterred by the literalrocky road ahead. This is easier said than done: digging with a pick and pickaxe is fun at first, but after a few hours, every muscle hurts, and you are completely exhausted by the evening. So, we were delighted to be able to get to grips with the dig site this year – supported by the museum's Friends – with a large team of 20 people. For the first time in 115 years of excavation history, several excavators were also used, deployed directly during the dismantling. The whole thing only became affordable because some employees quickly learned how to steer the heavy machines and how to use them more and more precisely.

Excavation and Discoveries 2023

For three weeks, we excavated the rock layers on up to four terraces, and in the process, discovered new skeletal remains, exciting geological findings were encountered and documented. It was a special experience that there were researchers from up to 12 different countries digging along, and contributing their knowledge. Our preparators, Isabell Rosin, Lucrezia Ferrari and Andreas Radecker made the recovery of the finds possible with their technical experience. Some skeletons had been disarticulated and transported by mudflows, others had crumbled into small fragments and were deposited in dry valleys after seasonal heavy rains. And, of course, the well-preserved three-dimensional bones that made the site famous were found again. Now, it has become clear that some animals died in a resting position, while others died of exhaustion after an unsuccessful struggle against the tough mud. Skeletons not embedded deep enough in the clay were washed free again by regular monsoon rains and gradually scattered in all directions. Thus, the new findings provided the incentive to consult Dr. Seemann's old excavation diary and compare it with the latest findings. This is, in fact, another special feature of our excavations: You can add to the detailed map of our predecessors and continuously expand on what has been recovered, so that you get a constantly growing three-dimensional picture of the gigantic burial site. Using a drone, which can precisely measure the terrain and all new finds, proved to be very helpful.

Conclusions about vegetation and climate in prehistoric times

The three thick rock layers containing the new finds, known since Professor von Huene's time, can now finally be studied in detail using the latest geological methods. For this purpose, many rock samples were taken for further processing in the laboratory. The 12-m-thick Knollenmergel succession in Trossingen, in fact contains numerous layers of claystone, which was originally deposited as mud in fine layers in a predominantly dry and hot climate. But these layers, apparently homogeneous, differ from metre to metre, so we could find evidence of a humid and densely vegetated landscape in the fossil-rich deposits, where more than 80 skeletons had come to light. Long fossilised roots testify to the vegetation, and heavily rolled clay layers prove frequent soaking and drying. This year, for the first time, we could reach and mine the deepest layer, which had last been exposed in 1932. In the three-metre-thick layer above, which contains only a few skeletons, evidence accumulates of much drier conditions, with stronger relief, in which the rare rainfalls left metre-deep gullies and wadis. Nodules up to 20 cm in size grew in the clay soil – giving the Knollenmergel (i.e., nodular marlstone) its name – and these show us that there must be much more geological time in the layers than had long been suspected: such nodules need tens of thousands of years in the appropriate climate to grow to that size. The seven-metre-thick purple layers above it were deposited in an environment that was again wetter and contained more skeletons and fossil roots. Still, the carcasses must have been exposed for longer here, so presumably, the annual sediment load was lower.

Around one million years of prehistoric local history

The Trossingen dinosaur site is thus a giant mass grave site that we are trying to decode with ever more refined methods. At the same time, the entire profile contains a climate archive documenting about one million years of prehistoric local history. It testifies to a temporally distant Baden-Württemberg on a much warmer planet, populated by the first enormousgiant herbivorous dinosaurs, which can be found almost all over the world because they were able to roam a massive supercontinent without significant barriers.

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