Nothosaurus marchicus: A reconstruction of a Sauropterygian from Winterswijk, The Netherlands

Dennis C Nieweg (The Netherlands) and Dick Mol (The Netherlands)

In April 2012, the exhibition Zeemonsters in Twente, opened its doors in Museum TwentseWelle in Enschede, The Netherlands (Fig. 2). The exhibition (held until the 28 October) told the story of the Triassic marine reptiles (Sauropterygians) found in the Dutch town of Winterswijk, in the Ankerpoort (Sibelco) quarry, and beyond.

The exhibition was opened by the well-known travel author, Redmond O’Hanlon (Fig. 3). One of the sauropterygians from the quarry is the marine reptile Nothosaurus marchicus. This reptile was reconstructed by artist Remie Bakker, from Rotterdam, who, together with Museum TwentseWelle and several international scientists, made a reconstruction completely different from the image created by the Czech artist Zdenek Burian in the 1960s.

Introduction

At the end of the Permian Period, approximately 250 million years ago, vegetation and animals went extinct in large numbers. During the Triassic Period, which followed, new life forms began to develop in the evolutionary space left by the mass extinction. The animals on land began to evolve into the dinosaurs of a later period. At the same time, small group of large reptiles, living in the area around the Palaeo-Tethys Ocean and smaller adjacent seas such as the Muschelkalk Sea, started to live in the water (Fig. 4).

In particular, a large sedimentation area on the northern border of the Palaeo-Tethys Ocean has been given the name ‘German basin’. The climate here was subtropical and the landscape was a hot, dry basin, like the Persian Gulf today. The weathering waste from the surrounding mountains was concentrated in this floodplain as sand. This is how the so called ‘Buntsandstein’ came into being’: an extremely thick layer of mostly hard, red, colourful sandstone. Life only existed in a few places, namely in those places where a bit of water could be contained. During the Middle Triassic (Anisian), a connection with the Palaeo-Tethys Ocean came into being and salt water poured into the bowl. This water partially evaporated, resulting in a higher quantity of already salty water. Only a few species could survive in these harsh circumstances. Some of them fared rather well, such as several types of shells (Muscheln in German), which, in the end, formed thick layers of grey lime: the Muschelkalk layer.

The first Sauropterygians (‘lizard flippers’), from the eastern part of the Palaeo-Tethys Ocean, settled in the ‘Dutch’ waters of the German Basin: the Muschelkalk Sea. Much later, other groups of Sauropterygians migrated to more southern areas, such as the south of Germany, Switzerland and Italy. These saurians started out as small marine reptiles in the Triassic age. However, later, in the Cretaceous Period, they evolved into large marine predators such as Plesiosaurs and Pliosaurs. The late Dr DA Hooyer was the first to describe saurian material from Winterswijk in 1959, using the (already familiar) term Nothosaur.

The muddy plain at Winterswijk was a so called ‘sabhka’. Nowadays, these can be found in the Middle East and in North Africa. They usually lie either near a warm, shallow sea or a lagoon. The clay is kept together by mats of lime-forming algae. These grew on the muddy, flat seafloor of the so-called ‘Wadden Sea’, which could be found at Winterswijk some 245 million years ago. This tidal area was part of a larger sea – the already mentioned Muschelkalk Sea. Dead marine reptiles from deeper parts of the sea, such as Nothosaurs and Pachypleurosaurs, washed up on the shallow plain, just like harbour porpoise drift ashore on the coast of the North Sea today.

Nothosaurs and Pachypleurosaurs

Nothosaurus was a marine reptile, approximately one to two metres long. Nothosaurs were highly adapted to marine life and they had paddles, as well as a muscular tail, which made it easier for them to glide through the water. Due to their lean bodies, dynamic neck and flat skull, it was possible for them to dart out wayside and grab a fish. Once captured in their sharp teeth, there was no escape. Nothosaurs were undoubtedly fish eaters. However, there is also evidence of Nothosaurs eating smaller congeners, if given the opportunity. In our collection, we found a pellet containing a Pachypleurosaur named Anarosaurus heterodontus, which may possibly have been devoured by a nothosaur in Anisian times.

The first nothosaur species from Winterswijk was described in 2003 as Nothosaurus winterswijkensis. However, in 2011, this species became synonymous to the Nothosaurus marchicus, which was an already known species (Fig. 5).

In 2009, a new species from the Winterswijk quarry was described: Nothosaurus winkelhorsti. This was a very small type of nothosaur that roamed the sea at the same time as its big brother. Two models of Nothosaurus marchicus have now been fashioned for the exhibition in Museum TwentseWelle – one male and one female.

Another nothosaur that looks like Nothosaurus was also found in Winterswijk, named Cymatosaurus. This is a saurian, which highly resembles the Nothosaur, but it belongs to a different group: the Pistosaurs. Nevertheless, its way of life resembles that of the Nothosaur. However, there are several differences between the genera Cymatosaurus and Nothosaurus, among others, the smaller nostrils and other characteristics of its skull. The species to which the Cymatosaurus of Winterswijk belongs is a question that is yet to be answered.

Other Sauropterygians present in Winterswijk are the so-called Pachypleurosaurs, which were small representatives of this larger group. They stood at the brink of the development of the Esauropterygians, which, in turn, also consisted of other groups, such as Nothosaurs and Pistosaurs.

Pachypleurosaurs hunted fish and were very capable swimmers. The average length of these animals lay between the 40 to 50cm. One of the trademarks of Pachypleurosaurs concerns the part of the skull in front of the eye socket, which is longer than the part of the skull behind the eye socket. This is an unmistakable difference compared to, for instance, a Nothosaur. Pachypleurosaurs have a small head with a long neck and were highly adapted to life in the sea. The specific species, which appeared at Winterswijk, were Anarosaurus and Dactylosaurus. The latter was the first representative of the Pachypleurosaurs in the German Basin, while Anarosaurus heterodontus was the first representative of this group in the western area of the German basin.

These were a different type of species than the ones that roamed the more southern areas at a later Triassic period, called the Ladinian, such as the genera Neusticosaurus and Serpianosaurus (Fig. 6).

In this later period, the Nothosaurs also became larger, such as Nothosaurus giganteus, which could grow up to 4m in length (Fig. 7).

The reconstructions

Thousands of fossil remains of the marine saurian Nothosaurus marchicus have been found in the quarries at Winterswijk (Fig. 8), which enabled the making of models closely resembling reality. Remie Bakker, from Manimal Works in Rotterdam, was asked to prepare two models, of a male and a female specimen. With the assistance of several scientists in the Netherlands and Germany, looking at other reconstructions in Stuttgart and Ingelfingen (Germany), and a dead monitor lizard, he prepared the fascinating models.

The starting point was the nothosaur fossils from the Winterswijk quarry. Looking at these fossils and comparing them to the modern anatomy of a monitor lizard (Remie Bakker dissected one especially for this purpose), it appeared that monitor lizards and the Nothosaurs have a completely different ‘body plan’. However, it was necessary to compare the fossils with a modern reptilian, although the genus Varanus (of which the monitor lizard is a member) belongs to the order Squamata, just like Mosasaurs.

Nothosaurs were not that large and, after measuring the fossils, an average size of 130cm was used for the reconstructions. Complete articulated specimens are not known from the Winterswijk quarry. However, in China and Switzerland, articulated specimens have been found. Unfortunately, these are not the same species, but the body plans are approximately the same (Fig. 9).

Note that in monitor lizards, the shoulders and pelvis are more or less vertical to the spine. This means that the lizard has strong limbs. The nothosaur othosaur had a highly developed spine, of which the shoulders and pelvis were directed in a more downward direction. All the strength was directed to a downward movement of the limbs. This was important for propelling it through the water, but also for directing the body. The strong ribs of the strong axial skeleton belonging to nothosaurs provided extra weight, useful for stabilisation and buoyancy. In addition, the strong skeleton served for the attachment of the muscles that made the creature highly manoeuvrable. It can be assumed that the creatures were at least as agile in the water as current sea lions. The body plan showed other features, such as a very flat head, highly developed (therefore muscular) caudal ribs (making tail propulsion very likely) and strongly developed thoracic ribs. Also, the limbs are distally flatter than proximal. This body plan fits the description of a highly specialised swimmer.

It is now clear that manoeuvrability and speed characterised this creature. As explained above, we decided to make two specimens. Two live size models were made, one (male) of 100cm and one (female) of 130cm. One of the main discussions was about the limbs. The question involved whether to have legs or flippers. Looking at the fossils, it seems that the toes are rigid, have vague joints, with no dominant direction of movement perceived. The bones are more rounded proximally, becoming flatter to the end of the ‘flipper’. This resembles turtles and dolphins. Taking this into consideration, and that the animal was highly manoeuvrable and had a flat axial skeleton and strong tail muscles, we decided the Nothosaurus must have had flippers instead of normal walking legs (Fig. 10).

Due to the strong tail, we decided the animal probably used the tail for propulsion and the flippers for steering. This image is contrary of the image created by the Zdenek Burian, who placed Nothosaurus on a rock, looking out over the ocean which he roamed (Fig. 11).

The eyes were located flattened in the skull and the muscles from the foramen behind the eye sockets made a strong bite possible. The teeth were turned inwards so that the prey could not escape (Fig. 12).

The covering of the skin is an assumption, but, since this is a fairly primitive creature, we decided on smooth, rounded scales (Fig. 13). Scales that were too rough would hamper streamlining in the water. We also increased the size of the scales on the elbows and the edges of the tail, and have created larger scales on the shoulders for protection.

Male and female Sauropterygians can be sexually distinguished by the humerus, which means that the male nothosaur had stronger, more pronounced upper arm bones. They probably held on to the females during mating, as turtles still do. This is the reason for the spores on the elbow and strong scales on the shoulders.

Another problem was the colour. We looked at Recent reptiles and birds, and decided to make the female a little darker than the male and gave the male more contrast. This was achieved by giving the male a blue stripe across the tail and, in general, giving the animals a dark back and white belly (Fig. 14). This rule seems to apply most to creatures with predators above them in the food chain and to animals that hunt.

After all these decisions, the two animals were made of a sculpting (wax) clay mounted on a metal frame, and casted afterwards into the beautiful models shown in this article (Figs. 15 to 18).

The replicas will be presented in a permanent display at the end of 2013. We will keep on checking the new fossil data which will come available, and maybe we will make a revised Nothosaurus 2.0 in the years to come (Fig. 18).

The authors can be contacted at the following addresses: Dick Mol at Het NatuurHistorisch, Westzeedijk 345 (Museumpark), 3015 AA, Rotterdam, The Netherlands; and Dennis Nieweg at Museum TwentseWelle, Het Rozendaal 11, 7523 XG, Enschede, The Netherlands.

Acknowledgements

The authors would like to thank Remie Bakker for making the two fabulous models and his explanation of how they were made; Hans Wildschut for providing some of the pictures; Henk Oosterink, the Quarry management; and all the members of the Workgroup ‘Muschelkalk’ Winterswijk for providing new specimens and new insights from the Quarry.

They would also like to thank Prof Martin Sander and Dr Nicole Klein from Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Bonn University; Dr Rainer Schoch, Staatliches Museum für Naturkunde (SMNS), Stuttgart; Dr Hans Hagdorn, Muschelkalkmuseum Ingelfingen; Dr John de Vos and Dr Paul Albers from NCB Naturalis, all for their help and our discussions with them about how Nothosaurus would have looked; and Dr Heinz Furrer, Paläontologisches Institut und Museum, Universität Zürich (PIMUZ), for lending us the specimens from Monte San Giorgio.

Further reading

Albers, P. C. H. & O. Rieppel, 2003. A new species of the sauropterygian genus Nothosaurus from the Lower Muschelkalk of Winterswijk, The Netherlands. – Journal of Paleontology 77(4): 738-744.

Albers, P.C.H., 2011. New Nothosaurus skulls from the Lower Muschelkalk of the western Lower Saxony Basin (Winterswijk, the Netherlands) shed new light on the status of Nothosaurus winterswijkensis. Netherlands Journal of Geosciences – Geologie en Mijnbouw 90(1): 15 -21.

Augusta, J. & Z. Burian 1964. Prehistoric Sea Monsters. Hamlyn Publishers.

Hooyer, D.A. 1959. Records of Nothosaurians from the Muschelkalk of Winterswijk, Netherlands. Netherlands Journal of Geosciences – Geologie en Mijnbouw 21: 37-39.

Klein, N. & Albers, P.C.H. 2009. A new species of the sauropsid reptile Nothosaurus from the Lower Muschelkalk of the Western Germanic Basin, Winterswijk, The Netherlands. Acta Palaeontologica Polonica 54 (4): 589-598.

Oosterink, H.W. 2008. Triassic reptiles from the Lower Muschelkalk of Winterswijk. Deposits 15: 34-38

Oosterink, H.W., W. Berkelder, C. de Jong, J. Lankamp & H. Winkelhorst, 2003. Sauriërs uit de Onder-Muschelkalk van Winterswijk. – Staringia 11.

Rieppel, O. 1999. Phylogeny and Paleobiogeography of Triassic Sauropterygia: problems solved and unresolved. Palaeogeography, Palaeoclimatology, Palaeoecology 153 (1999) 1-15.

Rieppel, O. & R. Wild, 1996. A revision of the genus Nothosaurus (Reptilia, Sauropterygia) from the Germanic Triassic, with comments on the status of Conchiosaurus clavatus. – Fieldiana: Geology, New Series 40: 1-85.