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Proboscidean tusks through time: a special case of excavation and displaying experience

Hoca

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Dick Mol (The Netherlands), Evangelos Vlachos (Argentina), Spyridoula Pappa (UK), Nikos Vasileiadis (Greece), Nikos Bacharidis (Greece), Vassilis Makridis (Greece), Evangelia Tsoukala (Greece)

Over the past 30 years, systematic excavations by the Aristotle University of Thessaloniki in Northern Greece have unearthed many Proboscidea fossils, including the longest tusks in the world at Milia (Grevena, Greece). Typically, as these fossils belong to the Museum of Geology, Palaeontology, Palaeoanthropology of Aristotle University, they should really be stored there. But due to the lack of necessary space in the museum, as well as the lack of sufficient funding to create replica fossils, it was decided to organise exhibitions near the fossil sites, which are peripheral units of the Museum of Geology, Palaeontology, Palaeoanthropology of the Aristotle University.

There are some disadvantages to exhibiting authentic fossils, such as:

  • their safety and security;
  • insurance;
  • the difficulty of establishing stable environmental conditions;
  • the need for ongoing preservation; and
  • the difficulty for researchers to study them once they are exhibited, as they are not readily available for research due to their large size.

All these factors are of particular importance when it comes to proboscidean tusks (which are extended incisor teeth), as they consist of very friable material that cannot be easily restored, such as dentin (ivory). In their original form, they have the same structure as the other teeth – enamel on the outside, dentin on the inside and a pulp cavity in the centre in most early proboscideans, whereas, in elephants, the enamel has been lost (Lister, 2014). In addition, the size in some cases makes it very difficult to handle them, as they need special maintenance that mainly requires knowledge and experience due to their specificity.

In these respects, this article demonstrates what needs to be followed for successful excavation and organisation of a fossil exhibition, without hindering the scientific work to be done. It refers to the most important sites of Greece with fossil tusks, such as Milia – Grevena (MIL), Kaloneri – Kozani (AKL), Kalamotó – Lagadá (KAL) and Neokaisareia – Pieria (NKP) (Fig. 1a). It is based on our experience derived from organising many excavations (headed by one of us ET) over decades, as well as 23 paleontological exhibitions in Northern Greece.

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Fig. 1(a). Map of Greece, with the location of the palaeontological sites described here (MIL Milia – Grevena, AKL Kaloneri – Kozani, NKP – Neokaisareia Pieria, KAL Kalamotó – Lagadá); and (b) cross section of a straight-tusked elephant tusk from Nea Lefki, Larissa (Tsoukala et al. 2011). The concentric circles can be confused with the ones of a bole tree for non-experienced people.

The management of a tusk – the experience from Greece​


Proboscideans (that is, a group of mammals, including elephants and their extinct relatives, such as mammoths and mastodons) are valuable, stratigraphic markers because their evolutionary characteristics provide evidence for the dating of geological strata. The tusks vary in size and especially in the morphology as a result of adaptation to feeding habits, and are used for display, offense, defence and food gathering (Maglio, 1973; Shoshani and Tassy, 1996; Shoshani, 1998).

They are generally larger in more advanced taxa and are part of Proboscidea sexual dimorphism with males having the largest. The size of the tusks grew exponentially in size during the Miocene and Pliocene, and the various taxa living during this period present up to four tusks in total composed mostly of solid dentin. The characteristic of dentin is that, when it is in a poor state of preservation, it can easily be reduced to small pieces the size of rice grains and thus restoration is impossible.

For this reason, for a palaeontologist, excavating tusks is the most difficult task among the other skeletal remains and requires care, skill, and experience. Of note is a story of the owner of a sand pit in Neapolis (Kozani, Northern Greece), who, while digging, discovered a tusk, which was thought to be a tree trunk as in Fig. 1b. The staff stopped working for a few hours trying to collect the specimen, but it collapsed into a pile of “grain”, due to the lack of any special preparation.

The management of discoveries, field maintenance, safe transport methods, and the display of fossil finds was a little-known cycle a few decades ago in Greece. What we know now is that, before the excavation process begins, a decision must be made about whether the new finds will be displayed in a museum, since this will affect the whole process.

The advantages of an original fossil display lie mainly in the fact that people like it and this will therefore attract visitors, contributing to the development of disadvantaged areas such as Grevena (West Macedonia). On the other hand, there are many disadvantages, such as the safety and security of the fossils, their constant preservation, and the difficulty for researchers in studying them, as they will not always be available for research.

In fact, tusks contain abundant information about the life and palaeoecology of proboscideans. Inferences can be made about their diet and the patterns of their lives, such as deciphering the season and age of death using a “growth ring” structure (Fisher, 1996). Microscopic observations of the internal structure of tusks can provide information about the life (for example, whether there was adequate or insufficient availability of food) of individuals, with a weekly or even daily precision. To make a long story short – a complete tusk of an elephant or an elephantine animal contains data on the life history to which the tusk once belonged.

Growth profiles in tusks can be used as indicators of sexual maturity. These findings, combined with the results from the isotopic composition of C3 and C4, provide information on the palaeoecology of extinct proboscideans (Koch et al., 1995; Cerling et al., 1997). However, all this research in the tusks needs to be completed before the exhibition of the fossils.

In the last 30 years, our team has organised a total of 23 paleontological exhibitions in local museums in Northern Greece. This was the first step towards the acceptance by the local communities and the scientific community of exhibiting original fossils. The success of this is further reinforced by the fact that all palaeontological exhibitions have contributed to the economic development of the localities, without hindering the scientific use of the fossils, so long as certain parameters are met.

The Pliocene fossil site of Milia​


Milia is a village in the regional unit of Grevena (in north-western Greece). Eleven fossil sites have been discovered in the Pliocene sediments of Milia during the last 25 years. The faunal association consists of 23 different species of animals that lived in the area 3.5 million years ago, including the Mastodons (Mammut borsoni) and Anancus arvernensis, indicating an early Late Pliocene biozone MN16a (Tsoukala, 2000; Guérin and Tsoukala, 2013; Tsoukala and Mol, 2016; Crégut-Bonnoure and Tsoukala, 2017; Lazaridis et al. 2019; Logchem et al. 2010; Vlachos and Tsoukala, 2016; Vlachos et al., 2018).

All the material collected is stored in the Natural History Museum of Milia. Two matching pairs of tusks were discovered by the systematic excavations at Grevena in 1996 (MIL1) and 2006 (MIL5). The Milia fossiliferous sediments are within the Geopark Grevena-Kozani (Tsoukala et al. 2010).

In 1996, a matching pair of tusks of Mammut borsoni, measuring 4.39m., was discovered along with its partial skeleton at the Milia 1 site in dry sand hills (Fig. 2a). Both incisors were in a friable and poor state of preservation, with plant roots penetrating them, as well as water seeping through the loose sand.

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Fig. 2. Excavation 1997: (a) Mammut borsoni tusks of Milia 1 (arrow: Milia village, oval: excavation site); and (b, c) the tusks in crosswise position (4.39m longest).

The fossils were carefully excavated using small hand tools and toothbrushes. They were preserved in situ with Paraloid dissolved in acetone, due to their poor state of preservation, and any broken pieces were also re-assembled using Paraloid. In fact, Paraloid B-72 is among the strongest, most stable, and reversible thermoplastic resins available for maintenance.

The newfound tusks proved a challenge for the excavation team in terms of managing the transport and storage methods. Normally, the fossils discovered by the Aristotle University of Thessaloniki (AUTh) teams are stored in the Museum of Geology, Palaeontology and Palaeoanthropology of AUTh where they belong. But the lack of space in the small museum, as well as the lack of a National Museum of Natural History in Greece, which could offer a great experience in education and science, led to the decision to create a local exhibition in Milia, where the fossils would be stored.

However, the transfer of the tusks to the Milia Museum proved to be quite difficult. Their crosswise position (Fig. 2b, c) and weight of Milia 1 tusks, estimated at about 300kg each, made them difficult to manage. And the location at the top of a sandy hill near the village of Milia did not make the situation any easier.

Due to a lack of sufficient finance, it was impossible to transport the entire tusks with the help of a crane. After much thought and discussion among the team members, it was decided that the tusks would be carefully cut into pieces, taking advantage of the already fractured areas of the fossils (e.g. groundwater percolation, roots of plants penetrated the fossils). A plaster jacket was created around each piece before cutting to secure the fossil during the cutting and transport process.

In 2006, during digging, a tusk was discovered by a crane operator, 14m below the surface in the sandpits of Milia 5. In 2007, a partial skeleton of Mammut borsoni, including the tusks, was excavated in Milia 5 (see The mastodon of Milia – the longest tusks in the world, by Dick Mol and Wilrie van Logchem). Their enormous lengths – 5.02 m and 4.58 m respectively, measured alongside the outer curvature – prevented the team from picking them up and transporting them all at once.

So far, these tusks are the longest tusks ever discovered in the world and are recorded in the Guinness Book of Records 2011 (Tsoukala, 2000; Mol and Logchem, 2009; Mol and Tsoukala, 2010; Tsoukala and Mol, 2010; 2016). However, they were also poorly preserved, as water had seeped into the loose sand deposits and plant roots had penetrated the fossils. In addition, the right tusk was destroyed in two points by the sandbar digger, although the tip of the tusk was intact and in its original position, so the exact size of the fossil could be confirmed (Fig. 3).

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Fig. 3. Excavation 2007: (a) the grid of the Milia 5 site; and (b) showing missing parts of the tusks that were destroyed by the digger crane in 2006.

The same excavation process used ten years ago was also followed this time. Sediment was carefully removed from the fossils using small hand tools, brushes and needles. The sediment-free surfaces were then impregnated with Paraloid several times to overcome the poor state of preservation and the risk of crushing during transport. This treatment made the material relatively robust, but any future attempts to retrieve biomolecules have been compromised. Therefore, for the purpose of future research, fragments of the tusk and of other tusks discovered in the excavation were collected and remained untreated, in case they were used in any biomolecule or isotope analysis.

The two parts destroyed by the digger were reassembled with double iron blades and marble glue (Fig. 4).

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Fig. 4. Reconstruction of the two damaged parts of the tusk: double iron blades are glued to the area of the destroyed tusk.

A flexible sheet metal was used to surround the fossil and create a mould filled with plaster and marble dust (Fig. 5a, b).

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Fig. 5. Reconstruction of the two damaged parts of the tusk: (a) creating a mould around the fossil using a flexible metal sheet; and (b) filling the mould with plaster and marble dust.

After drying, the sheets were removed, and the plaster was given the shape of the tusk (Figs. 6 and 7).

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Fig. 6. Reconstruction of the two damaged parts of the tusk: removing the mould after drying.
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Fig. 7. Reconstruction of the two damaged parts of the tusk: polishing the plaster surface of the tusk to resemble the original fossil surface.

For the transportation of the tusk, the same methodology as the excavation from 1997 was used. A plaster mould was created around the fossil, which was then split into three pieces, taking advantage of the already existing fractures (Figs. 8-10).

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Fig. 8. After the preservation of the tusks: (a) covered with wet paper; and (b) creating aplaster jacket along the entire length of the tusk for safe transport.
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Fig. 9(a). The complete tusks in situ; and (b) in the plaster jackets.
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Fig. 10. Part of the tusk ready for movement.

The display of the fossils in the museum was implemented in two phases. In the first phase in 2007, the pieces of the tusks were safely assembled in the museum. There, they were carefully removed from the plaster moulds, and they were placed onto the wooden braces (later replaced by special plexiglass supports, made by one of us – NB) based on their curvature and torsion according to the special marking carried out during preparation at the excavation site.

The construction of the braces to match the curvature and torsion of the tusks, and the correct placement of the tusks onto the braces, was supervised by of one of us (DM) (Fig. 11). The plaster part of the tusk restored during the excavation was sculpted and painted by the artist, Dimitra Labretsa, under the supervision of DM (Fig. 12a).

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Fig. 11. First phase of the display in 2007: (a) careful removal of the plaster moulds; and (b) placing the pieces of the tusk on the wooden braces following the correct curvature and torsion.

The second phase concerned the transfer of the fossils and tusks of the first exhibition from the former Milia community building (Fig. 12b) to the adjacent renovated building of the former school of Milia. In 2018, a large Greek-Dutch cooperation project took place, so that the transfer and promotion would be carried out following scientific criteria. In the new exhibition, the two pairs of tusks are now in their anatomical positions.

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Fig. 12. First phase of the display in 2007: (a) artist Dimitra Labretsa painted the plaster part of the tusk to match the original fossil; and (b) final display at the museum in the former community building of Milia.

The first step was to select the correct position for each tusk, to match the proper anatomical position, angle, torsion, and curvature that the tusks had in the skull. Choosing the proper materials was of the utmost importance for the construction of the metal bases that would support the two pairs of tusks.

Scientists and technicians considered even the slightest of details, such as welding the iron parts to match the curvature of each tusk, which was marked with tapes. Metal triangles were glued between the pieces of the tusks for better stabilisation. Only with this precision can the tusks be positioned accurately. When the iron support was ready, a rehearsal was held in the old building to check the correct position of the pieces (Figs. 13-17).

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Fig. 13. Second phase of the transfer process from the old building to the new exhibition in 2018: the definition of the correct position of each tusk – the curvature and torsion are marked with tapes.
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Fig. 14. Second phase of the transfer process from the old building to the new exhibition in 2018: the profilometer helps in the accuracy of the curvature.
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Fig. 15. Second phase of the transfer process from the old building to the new exhibition in 2018: the metal rods are adjusted by hand to the correct curvature and attached to the tusks.
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Fig. 16. Second phase of the transfer process from the old building to the new exhibition in 2018: the technician welds the iron pieces, and small metal triangles to stop the pieces from sliding.

The metal bases were transferred and painted with stainless paint (Fig. 17b).

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Fig. 17. Second phase of the transfer process from the old building to the new exhibition in 2018: (a) a rehearsal is held in the old building to check the correct placement of the pieces; (b) the metal bases were transferred and painted with stainless paint

To safely transport the tusks, the same methodology was applied as in the excavations, meaning that the tusks were once again cut back into the same pieces they were cut into during the excavation, taking advantage of the natural breaks in the tusks during the fossilisation process. Then, they were carefully carried by hand, one by one, to the new exhibition building, so the pieces were gradually added to the special bases and their position is checked again (Figs. 18 and 19).

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Fig. 18. Second phase of the transfer process from the old building to the new exhibition in 2018: the tusks were carefully carried by hand, one by one, to the new exhibition building.
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Fig. 19. Second phase of the transfer process from the old building to the new exhibition in 2018: they are gradually added to the special bases, and their position is checked again

This made sure that the final placement of the tusks reflected their anatomical position. This was a complex procedure that required teamwork and a combination of scientific and technical skills. Finally, after the appropriate detailed maintenance, the tusks are now displayed in their new correct positions (Fig. 20). All the fossils were placed in wooden showcases and onto plexiglass braces. A safe glass cabinet, which maintains the appropriate constant relative humidity and temperature, covers the showcases and the fossils (Tsoukala et al. 2018).

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Fig. 20. Second phase of the transfer process from the old building to the new exhibition in 2018: the tusks are now in their new anatomical display.

The Middle Pleistocene fossil site of Kaloneri​


Kaloneri is a village in the regional unit of Kozani (Northwest Greece). In 2006, during road construction, a skull fragment with the two tusks was discovered in a poor state of preservation. The construction process of the road was discontinued immediately, and rescue excavations were carried out with the co-operation of the Archaeological Museum of Aiani, the Ephorate of Paleoanthropology – Speleology of Northern Greece (Ministry of Culture) and the Aristotle University of Thessaloniki (Fig. 21a).

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Fig. 21(a) Excavation at Middle Pleistocene Kaloneri fossil site AKL; and (b) the part of the alveoli of the skull with the tusks.

The material was in a friable state and the skull was destroyed by a bulldozer. Only the proximal end of the tusk sockets and the complete left and right tusks remained (Fig. 21a, b). For safe transport, plaster jackets were used, which were kept at the school in the town of Kaloneri (Fig. 22a).

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Fig. 22(a) plaster jackets for the safe transport of the material; and (b) maintenance with Paraloid B-72 injections.

Two years later, in the summer of 2008, preservation took place at the Milia Museum, where the tusks were kept until the end of the same year. Because of their poor state, they were largely preserved using Paraloid injections (Fig. 22b), while artistic plaster was used to fill the gaps in the tusks and then polished (Fig. 23a).

Due to this poor condition, the team designed an iron frame to support the tusks to hang on the wall, in a natural position, when they were moved and first exhibited at the former Town Hall of Kaloneri, in 2008 (Fig. 23b).

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Fig. 23(a) artistic plaster is used to fill the gaps in the damaged tusks; and (b) construction of an iron frame to support the unequal tusks during their first exhibition in the former municipal building of Kaloneri (Mol and Tsoukala 2014).

The tusks were accompanied by an elephant painting by the artist Dimitra Labretsa, under the supervision of DM (Fig. 23b).

In 2012, the specimen was moved to the Trampantzion building in the town of Siatista, in a room next to that of the Historical Palaeontological Collection of Siatista (Fig. 24).

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Fig. 24. The final display of the tusks and a life-size mural showing a scenario for the reason behind the breaking of the right tusk: the fight of two male individuals of the Pleistocene straight-tusked elephant, Elephas antiquus, in musth, in the Trampantzion building in Siatista (Mol and Tsoukala 2014).

The dimensions of the tusks indicated a large, male individual with an extreme divergence of the tusks that is typical of the straight-tusked elephant (Elephas antiquus). The cross-section of both tusks shows that they are of undulatory shape, and in their original anatomical position. The frontal and lateral sides of the tusks are strongly flattened.

After mounting the specimens in their original position, the most important result was that it firstly became clear that the right tusk is pointed downwards and outwards, and slightly curved in frontal position. The left tusk is pointed downwards and strongly outwards, and weakly forward; the tip is curved towards the axis. Secondly, to reflect the divergent position of the tusks in the straight-tusked elephant that is so characteristic of this extinct representative of the Proboscidea.

The original anatomical positions of the tusks in the alveoli indicate that the carcass of the animal was deposited at the site shortly after death. The tip of the left tusk has a narrow and pointed shape, and the tooth is of its natural length. The right tusk, which is much shorter than the left one, was broken during the lifetime of the animal. However it was used by the animal after it became damaged, which is shown by the polished, regrown tip, giving it a very bold morphology (Tsoukala et al., 2011).

In 2014, the mural (6.30m x 3.50m) on the wall of the display room housing the Kaloneri Elephant shows a scene from hundreds of thousands of years ago – in almost life-size, the mural envisions two bull straight-tusked elephants in musth fighting with each other, trying to win favour with a nearby herd of female elephants (Fig. 24). The story was created by the artist Remie Bakker, also supervised by DM, during the VIth International Conference on Mammoths and their Relatives (Mol and Tsoukala, 2014).

The Early Pleistocene fossil site of Kalamotó​


Kalamotó (Nea Kalindoia) is a village in the municipality of Lagadá, near Thessaloniki. Two mammalian sites, Kalamotó 1 (KAL) in grey sediments (Fig. 25) and Kalamotó 2 (KLT) in red-brownish sediments (Fig. 26) in the Mygdonia Basin have yielded several large mammalian remains of Early Pleistocene age (about 1.2-1.5 Ma) (Tsoukala and Chatzopoulou, 2005; Kostopoulos et al. 2018). Excavations and research in the area began in 2000 and the fossils are housed in the Natural History Museum of Nea Kalindoia.

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Fig. 25. Excavations at Early Pleistocene Kalamotó fossil sites: in the grey sediments of the Kalamotó 1-KAL site.
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Fig. 26. Excavations at Early Pleistocene Kalamotó fossil sites: in the red-brownish sediments of the 2-KLT).

The southern mammoth, Mammuthus meridionalis, tusk was discovered in 2002 by the villager I Gakis, in the grey sediments of the Vasmouras stream (Fig. 27). The dimensions of the curved and slightly torsioned tusk are 2.05m long and 12cm in diameter, and compared to those of the same species, indicate that it belongs to a female individual of this species. An important identification feature of southern mammoth tusks is the cross-section of the tusk – it is usually flattened at the front, which is not the case in the almost circular tusks of other Probocideans.

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Fig. 27. Excavations at Early Pleistocene Kalamotó fossil sites: the southern mammoth (Mammuthus meridionalis) tusk in situ, in Kalamotó 1-KAL site.

The fossil was in a poor state of preservation and so was excavated with the utmost care. The sediment was carefully removed from the surface of the tusk using small hand tools and toothbrushes. Paraloid was applied to the fossil after it was cleaned of sediment and, once it became firm, it was collected in pieces, in four plaster jackets. For 14 years it was exhibited in the Natural History Museum of Nea Kalindoia (Fig. 28).

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Fig. 28. Excavations at Early Pleistocene Kalamotó fossil sites: the tusk KAL 59 in plaster jackets at Palaeontological Exhibition of the Municipal Museum in Kalamotó.

As mentioned above, tusks are made up of dentin and when dentin is in a poor state of preservation, it turns into small fragments, resulting in the destruction of the tusk. Because there was an imminent risk of destroying the tusk (Figs. 29 and 30), in 2016, the Lagadá Municipality funded its restoration, authorising one of us (NB) to undertake the project.

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Fig. 29. The poorly preserved tusk mammoth KAL-59.
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Fig. 30. Paraloid is applied to the tusk to increase its strength for the next stages of the restoration process.

The initial idea was to reinforce the tusk with Paraloid until it was firm enough to punch through the centre of the tusk pieces (Fig. 30), and then insert stainless iron rods into them and finally fix them together using the iron rods inside as a support to hold their weight.

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Fig. 31. Copper pipes and iron rods are drilled into the centre of the tusk pieces.

Although the base of the tusk was the densest part, it was impossible to retain the rest of the tooth due to the poor state of preservation. To overcome this, a vast amount of Paraloid was poured into the fossil until it became durable enough to handle. Copper pipes were drilled into the centre of the four tusk pieces and stainless iron rods were inserted into these copper pipes (Fig. 31).

A liquid – like honey – glue was then used to stabilise the iron rods and the gaps between each piece. This glue flows and penetrates everywhere, and when cooled with a catalyst, it becomes as durable as stone. The four pieces were fixed together, taking into consideration the original curvature and torsion of the fossil. Between the first and the second pieces of the tusk, there was a contact gap that needed to be filled. The gap was reinforced by a wire mesh (Fig. 32) and a cardboard mould was used to fill the gap with a mixture of plaster, acrylic putty and titanium (Figs. 33 and 34).

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Fig. 32. Reinforcing the gaps with wire mesh.
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Fig. 33. Filling the gaps between the pieces of the tusk with a mixture of plaster, acrylic putty and titanium.
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Fig. 34. Another image of filling the gaps between the pieces of the tusk with a mixture of plaster, acrylic putty and titanium.

In many places, its outer surface was peeled, with many cracks and fractures. The fallen pieces that remained in the plaster jackets were inserted into the tusk like a puzzle wherever possible. But most of them had become crumbs, so they were made into powder by grinding them up and then used as a binder together with glue, filling the gaps of the tusk. The surface was carefully polished (Fig. 35) and finally, the unique (in Greece), nearly complete female mammoth tusk is now exhibited in the Kalamotó Museum (Fig. 36).

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Fig. 35. Polishing of the plaster surface to match the surface of the tusk.
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Fig. 36. The tusk after its laboratory restoration by one of us (NB) is exhibited in the Museum.

The Miocene fossil site of Neokaisareia​


Neokaisareia is a village in the municipality of Katerini (Central Macedonia, Greece). Scattered mastodon skeletal remains were found and excavated in 2014 and 2016 by the excavation team of the Thessaloniki Aristotle University, including a tusk of a female mastodon Mammut sp. (M. obliquelophus?) (Konidaris and Tsoukala, 2020) of Late Miocene age (about seven million years ago).

Plaster jackets were created around each fossil to safely transport them to display them in the Neokaisareia exhibition, because of their poor state of preservation. The sandy sediments of the excavation were sifted for other fossils, mainly micromammals, but to no avail. The fossils were carefully cleaned in the exhibition building using small hand-tools, toothbrushes, and air-compressed needles. The fossils are now on display in the Palaeontological Exhibition created in Neokaisareia, with the assistance of the local cultural group “Mastodontas” (Fig. 37)

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Fig. 37. Mastodon tusk from Neokaisareia NKP: on display in the exhibition hall of Neokaisareia: the first tusk of the female Mammut sp. (M. obliquelophus?).

Research in the area continued and eventually, in 2021, a second fossil site was discovered, which revealed a second tusk along with part of the alveolus. Because the location of the new find was near a dirt road and had already been partially exposed, a rescue excavation was deemed mandatory.

The AUTh team arrived at the site and successfully excavated the complete 3m-long tusk within a few hours, in a single day (Figs. 38 and 39).

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Fig. 38. Rescue excavation of a mastodon tusk from Neokaisareia NKP: location of the tusk on a road path.
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Fig. 39. Rescue excavation of a mastodon tusk from Neokaisareia NKP: (a) cleaning of the sand deposits with brushes and small tools; and (b) the tusk covered with wetpaper.

The tusk was in a moderate preservation. Sediment was removed from the fossil with small hand-tools and brushes and covered with wet paper (Fig. 39).

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Fig. 40. Rescue excavation of a mastodon tusk from Neokaisareia NKP: further plaster jacket construction around the tusk for safe transport.

A plaster jacket was created around the tusk for safe transport to the Exhibition Hall (Fig. 40 and 41).

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Fig. 41. Rescue excavation of a mastodon tusk from Neokaisareia NKP: (a, b) plaster jacket construction around the tusk for safe transport; and (c) overturned, ready to move to the laboratory.

After preservation by one of us (BM), the tusk of a male mastodon Mammut sp. (M. obliquelophus?) was exhibited in the Hall with the rest of the fossils, telling an interesting story about the proboscidean ancestors that lived in the area millions of years ago (Figs. 37 and 42).

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Fig. 42. Rescue excavation of a mastodon tusk from Neokaisareia NKP: the tusk on display in the exhibition hall of Neokaisareia.

Discussion​


The four sites at Milia (Pliocene), Kaloneri and Kalamotó (Pleistocene), Neokaisareia (Miocene), together with the palaeontological excavations and discoveries of proboscidean tusks through time that are described in this article, all have in common that some of the material extracted was exhibited in new local museums created in the areas of the research and excavation.

In our case, the decision to organise palaeontological exhibitions was made due to lack of central storage space and lack of sufficient funding to create fossil replicas, but mostly stemmed from our passion to promote palaeontology within society.

Judging from our team’s over-30-year-experience in fossil excavations, preservation and display, it is obvious that it is possible to use original fossils as exhibition material in museums. However, the decision to display them should be made at the beginning, because it leads to a specific process in connection with cleaning, consolidation and publication.

The security of fossils from environmental and social perspectives is of the outmost importance. This can be achieved by using glass showcases, with covers to properly secure and protect the fossils (Larkin, 2010). In addition, braces fitted to properly match those of the fossils must be used, as well as controlling temperature and humidity around the specimen.

Another important factor is the preservation of fossils on a case-by-case basis. In general, the scientific community agrees that fossil preservation usually prevents some of the research processes (Shelton and Johnson, 1995; Andrew, 1996; Aldhouse-Green and Pettitt, 1998). In this regard, scientific research and publication of the fossils need to be completed before the application of techniques that may alter the surface of the bone or impose a negative effect on subsequent studies, such as DNA, C14 and stable isotope analysis. For this reason, the use of reversible maintenance products like Paraloid-72 is recommended (Koob, 1986; Shelton and Chaney, 1994; Shelton and Johnson, 1995; Down et al., 1996; Polin, 2012).

For the sake of the display, some fossils may need to be preserved with materials that are not easily removable, such as plaster or to an extent that can hinder or compromise any future research. In these cases, some material is better left untreated.

In the case of highly preserved fossils like the mammoth tusk from Kalamotó, all research was concluded ten years before the fossil was processed. Although, even in this case, treatment was deemed necessary due to the very poor state of preservation and due to the imminent risk of complete destruction of the fossil.

Finally, the safety and environmental conditions of the fossils, among other factors, must be considered before creating an exhibition.

Therefore, to reiterate, the decision to create an exhibition should be made before the excavation, as it can and will affect the whole process. The main advantage lies in the fact that fossil displays tend to attract visitors and thus they contribute to the development of mostly degraded areas.

On the other hand, there are several disadvantages, such as the safety and security of fossils from social and environmental pressures, and the extensive preservation they require since they are more exposed compared to simple storage. In addition, there is difficulty for researchers to study them once they are exhibited. In this respect, it is wise to complete most of the research that needs to be done prior to final display of the fossils and before the extended application of preservation materials.

Conclusions​


A total of 23 paleontological exhibitions have been organised in northern Greece during the last 30 years, from the systematic excavations by the Thessaloniki Aristotle University team. Among the fossils on display, the most impressive and recognisable by visitors are the proboscidean tusks. Their size, their specificity, and the story that tell us put them at the top of public interest, at least in Greece.

Furthermore, the way they evolved over millions of years greatly helps the palaeontologist identify the various species of proboscideans and to determine indirect dating, thereby becoming valuable guides to stratigraphy.

On the other hand, the way of excavating, transporting, and exhibiting them is the most difficult work compared to other vertebrate fossils. This is due to the particularity of their constitution, because dentin is very sensitive both to the process of ossification and the rest of the collection process. If it is mismanaged, it immediately risks turning into rice-sized fragments that are impossible to reconstruct. Consequently, the palaeontologist must organise the preparation very carefully before unearthing the tusks from the excavation site.

Knowledge and experience are needed here, because the conditions of fossilisation change within a few centimetres of the sediment and thus are difficult to fit into standard, professional maintenance rules. In each of the cases mentioned above, new ways of dealing with the various problems had to be invented separately, so that the result is both scientifically correct and attractive.

The cases of the tusks discussed in this article are characteristic both for the variety of problems faced and for the results. The case of Milia was also recognised with a Guinness world record, which is impressive for the local people, and for Kalamotó, which now has the only complete southern mammoth tusk on display in Greece.

Acknowledgments​


We are thankful to all members of the AUTh team (students and collaborators) who participated in our excavations for decades and brought to light precious fossils for Science, Education and Society. We also thank Iordanis Poimenidis, the special artist Remie Bakker and his co-worker Tone Skelton, the photographer Hans Wildschut, and the members of “Mastodontas” Association of Neokaisareia for their contribution to our research.

Finally, we are very grateful to Jon Trevelyan of Deposits for improving and editing the manuscript with regard to the English language.

About the authors​


Dick Mol is the corresponding author for this article and is based at the Natural History Museum, Rotterdam (3015 AA, Rotterdam). He can be contacted at [email protected].

Evangelos Vlachos is with CONICET (the Argentinian National Scientific and Technical Research Council) and Museo Paleontológico Egidio Feruglio, Av. Fontana 140, 9100 Trelew, Chubut, Argentina.

Spyridoula Pappa is based at the Department of Earth Sciences, Natural History Museum, London, UK.

Nikos Vasileiadis is also based at Aristotle University, School of Geology, Thessaloniki, Greece.

Nikos Bacharidis is a researcher in Thessaloniki, Greece.

Vassilis Makridis is a speleo-researcher in Kilkis, Greece.

Evangelia Tsoukala is based at Aristotle University, School of Geology, Thessaloniki, Greece.

Further reading​


The mastodon of Milia – the longest tusks in the world, by Dick Mol and Wilrie van Logchem (The Netherlands)

Mammoths and the Mammoth Ivory Trade, by Dick Mol and Bernard Buigues (The Netherlands)

Fossil bones from the North Sea: An easy to way to collect fossil remains from the Ice Age? by Dick Mol (The Netherlands)

New museum in northern Greece: The Siatista Historical Paleontological Collection, the first record of a stegodon in Europe and the making of the straight-tusked elephant, by Dick Mol (The Netherlands), Evangelia Tsoukala (Greece), Evangelos Vlachos (Greece), Anna Batsi (Greece), Hans Wildschut (The Netherlands), Dimitra Labretsa (Greece) and Wilrie van Logchem (The Netherlands)

Exceptional mammoth discovery from the North Sea, by Dick Mol (The Netherlands)

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