Diversity of trace fossils from the Anisian (Middle Triassic) of Winterswijk, The Netherlands
Henk Oosterink (The Netherlands)
Ichnofossils are the non-body remains of organisms. This group of fossils includes burrows, borings, tracks and any other trace formed by the life activity of organisms. They are very important in determining the ecology of extinct organism – although it is not always possible to link a single ichnofossil to the organism that made it. They are also useful in palaeoenvironmental analysis and solving other sedimentary problems.
As a result of finds of, for example, reptile bones, the Middle Triassic quarry of Winterswijk (Anisian) is famous for its ichnofossils of both vertebrates and invertebrates (see my article in Issue 15 of Deposits). However, also well known from this quarry are the footprints and tracks made by several Triassic reptiles. In addition, a great number of traces from invertebrates have been found there and, in this article, I will show and describe some of them.
Muschelkalk
During the Muschelkalk part of the Anisian (240mya), the Central European area (Germany, Poland, Denmark, the Netherlands and north-eastern France) was a shallow sea, referred to as the Muschelkalk Sea. During this period, there were frequent regressions and transgressions and, perhaps, there were also tides. In addition, along its coastline arose abundant, so-called sabkhas (flat, coastal deserts), which were places where algae and cyano-bacteria grew during high tides and floods (Fig. 1).
In this way, bio-laminates were created and, over millions of years, a thick covering of carbonate laminates developed. Eventually, these petrified into limestone. For example, the Muschelkalk sediments of Winterswijk are 50m thick and, in other parts of Central Europe, they are even thicker.
During this period, the climate was dry and very hot. The Winterswijk area was situated about 25N, so fairly near the equator. As a result of continental drift, it is now situated at about 52N. Along the high water marks, all sorts of reptiles searched for food and it is supposed that the dead bodies of marine reptiles and fishes, which drifted ashore, were food for them (Sander and Klein, 2006).
Tracks and footprints of these reptiles remained in the calcareous-clay laminates, which then hardened. In later phases, the tracks filled up with calcareous-clay and the footprints were preserved in the sediment (Fig. 2). In this way, we now find many reptile tracks in several layers and places. In fact, Diedrich (2008) mentions 75 locations in the Central European area.
Reptile footprints and tracks
In the Winterswijk quarry, five different reptile-tracks and footprints can be validly distinguished and are found in mud-cracked bio-laminates and sometimes in ripple marks. When these footprints are found, there are always two of them – positive and negative – that is, the original footprint and the cast.
The footprints of Rhynchosauroides peabodyi (Faber, 1958) are generally the most frequently found. Most of the time, the print of the forelimb is more deeply impressed than the hindlimb, because the weight of the reptile was on the front of its body. In fact, the fifth toe of the hindlimb has often left no impression at all and only the impression of the nail is visible. Further impressions of scales on the lower side of the feet are sometimes visible. In 2005, an excavation in the quarry by the universities of Bonn, Utrecht and Amsterdam found a Rhynchosauroides peabodyi track of about 12m (Fig. 3). In other layers, they found trampling horizons.
Other tracks are referred to as Procolophonichnium haarmuelensis (earlier called Procolophonichnium winterswijkensis, Demathieu and Oosterink 1983). These are from smaller reptiles than Rhynchosauroides peabodyi and smaller prints often mean more manus (the terminal segment of the forelimb) and pes (the terminal segment of the hindlimb) are present in one trail on the slabs (Fig. 4).
Another, much rarer tract is Brachychirotherium paraparvum Demathieu and Oosterink 1988 (Figs. 5 and 6). The print of the hindlimb is about twice the size as the foreleg. Usually, the impressions of the scales and nails can also be seen. In one suchtrack, the impression suggests that the animal slid while walking, indicating that the mud was slippery at the time.
Another track that can be found is Phenacopus faberi Demathieu and Oosterink, 1983 (Fig, 7). Most of the time, this is accompanied by a swinging tail-print. It looks a little bit like Procolophonichnium haarmuelensis, but good examples are rare.
Finally, there is Coelurosaurichnus ratumensis Demathieu and Oosterink 1988 (Fig. 8). This has only been found once. It consists of six big prints of both manus and pes. The forelimb has five toes and the hind-leg only three, which are substantially longer and bigger.
Swimming traces of fishes
In a layer of very fine-grained limestone, swimming trails of fishes have been discovered. These are called Undichna and are interpreted as being oscillation scratches made by the fins of a swimming fish touching the seabed. They are made up of sinusoidal waves, which were probable produced by coelacanths (oral information by Jacob Benner (Medford, USA) and Dirk Knaust (Stavanger, Norway)).
These kinds of swimming traces have also been described by Simon et al (2003) as being Parundichna (Fig. 10). This is possible, because, in the Winterswijk quarry, an almost complete coelacanth fish and also several loose scales have been found.
Traces of invertebrates
Invertebrate-traces are divided into a number of cluster-names, representing how the traces were caused. In this way, the following classification division can be made:
- Repichnia. The movement of animals over a surface leaving tracks and also worm-crawling traces, swimming traces and so on.
- Fodinichnia. The feeding of deposit feeders, resulting in U-shaped, branching and sinuous burrows (Figs. 12 and 13).
- Pascichnia. The feeding of grazer.
- Domichnia. A living burrow or boring.
- Cubichnia. A temporary hiding or resting trace (Fig. 14).
- Fugichnia. A structure produced by an animal escaping in panic from threat.
For many traces, it is impossible to work out exactly their origin, so it is not possible to classify the traces in the above groups. Therefore, it is often impossible to determine these traces by genus (ichnogenus) or species (ichnospecies) name. However, comparisons between recently made traces and fossil traces have been carried out. Brady (1947), for example, compared recent tracks of scorpions with traces in Permian Coconino sandstone in the USA.
And what about the makers?
Whenever fossil footprints, tracks and traces are considered, it is inevitable that there will also be a discussion about the makers. However, only when the maker is fossilised at the end of a track, can we definitely say something about the vertebrate or invertebrate animal that made it. Unfortunately, this is extremely rare.
Therefore, a link between a track-fossil and body-fossil is mostly supposition. As a result, a parataxonomic system has been established for tracks and traces. Unfortunately, this system of ichnofossil-names does not correlate with names of body-fossils. However, palaeontologists still try to link, for example, reptile-bones from the legs with reptile footprints.
Acknowledgements
My thanks to Mr Arent Noordink (Aalten, Netherlands) and Mr Martien Oosterink (Winterswijk, Netherlands) for their help and some photos. My thanks also to Mr Jacob Benner (Medford, USA) and Mr Dirk Knaust (Stavanger, Norway) for their help in identifying some traces. The pictures are mostly from the collection of the author.
References
Brady, L.F. 1947. Invertebrate tracks from the Coconino sandstone of Northern Arizona. Journal of Paleontology 21, 5: 466 – 472.
Bromley, R.G. 1990. Trace fossils. Biology and taphonomy. Unwin Hyman Ltd, London.
Demathieu, G.R. and H.W. Oosterink. 1983. Die Wirbeltier-Ichnofauna aus dem Unteren Muschelkalk von Winterswijk. Die Reptilienfährten aus der Mitteltrias der Niederlande. Staringia 7. Ned.Geol.Ver.
Demathieu, G.R. and H.W. Oosterink. 1988. New discoveries of ichnofossils from the Middle Triassic of Winterswijk (the Netherlands). Geologie en Mijnbouw 67: 3 – 17.
Deposits 15: 34 – 38.
Diedrich, C. 2008. Millions of reptile tracks – Early to Middle Triassic carbonate tidal flat migration bridges of Central Europe – reptile immigration into the Germanic Basin. Palaeogeography, Palaeoclimatology, Palaeoecology 259: 410 – 423.
Haubold, H. 1984. Saurierfährten. Die Neue Brehm-Bücherei. A. Ziemsen Verlag, Wittenberg Lutherstadt.
Oosterink, H.W. 2008. Triassic reptiles from the Lower Muschelkalk of Winterswijk.
Sander, P.M. and N. Klein. 2006. Terrestrial reptile tracks and marine reptile body fossils from the Lower Muschelkalk (Middle Triassic) of Winterswijk, The Netherlands. Journal of Vertebrate Paleontology 26, 3 Abstracts 119A.
Simon, Th., H. Hagdorn, M.K. Hagdorn and A. Seilacher. 2003. Swimming trace of a coelacanth fish from the Lower Keuper of South-West Germany. Palaeontology 46, 5: 911 – 926.