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Francien Dieleman

F.E. (Francien) Dieleman, MSc., Research associate - Biodiversity Discovery


Email: francien.dieleman@naturalis.nl
Phone: +31 (0)
Room number: C.01.08, Darwinweg 2
“fascinated by fossil voles”

Though I’m interested in all aspects of geology and palaeontology, since I was a child, I now focus on the geology of the Netherlands, in particular the provinces Zeeland and Zuid-Holland in the southwest of the Netherlands.

My speciality is biostratigraphy with a special group of microvertebrates: fossil Arvicolids (voles and lemmings; Dutch: woelmuizen en lemmingen).





I became interested in voles after finding a small jaw on a beach during a trip to Zeeland in 2004. I had no idea what animal it belonged to, till I made an appointment with Naturalis microvertebrate specialist dr. Lars van den Hoek Ostende, who identified the jaw as Arvicola terrestris (watervole, waterrat). Eversince I'm fascinated by fossil voles, and I spent a lot of time collecting them from beaches and researching my own finds, those from other collectors, and from collections in the Netherlands and abroad. Since 2007 I am research associate at Naturalis Biodiversity Center.


Research interest

Arvicolids are the most common rodents of the northern hemisphere since the Pliocene. They inhabite our world in large numbers. Predators like owls are mainly responsible for accumulation of bones and teeth in pellets. Bones and teeth of small mammals disintegrate rapidly within a few month on soil surface, but when pellets are deposited in rivers or lakes, this is in favour of their preservation in sediments. In the Netherlands many sediments are reworked during regressions and transgressions of the North Sea. As a result fossil Arvicolid remains can be found almost anywhere in our country, especially in boreholes and on beaches where sand dredged from the North Sea is deposited.

Usually all that is left of such creatures is their teeth: incisors and molars, only a few millimeters in size, but still visible by the naked eye. Besides being beautiful objects with intriguing shapes, when viewed under a microscope, molars appear to be very useful too.

The rapid evolution of some vole taxa, which can be seen in their molars, makes them very interesting as biostratigraphic markers for the Pliocene and Pleistocene.


taphonomy, voles, arvicolids, geology, taxonomy, pleistocene, pliocene, biostratigraphy

Current research topics

research projects:

I'm investigating fossil small mammals in the Netherlands and Belgium. I focus on fossil voles (Arvicolids), especially those abundantly found on the beaches in sand dredged from the North Sea and its estuaries. I also use my knowledge of fossil voles to contribute to stratigraphic projects in the Netherlands.

Vole taxonomy

At the moment I'm mainly working on Pleistocene and Late Pliocene voles, taking a special interest in the molar morphology of molars of members of the Mimomys polonicusMimomys pliocaenicus lineage (watervoles of the Late Pliocene/ Early Pleistocene), and the Mimomys saviniArvicola terrestris lineage (leading to the present watervole). This is because these are the most common voles that can be found on the shores of Zeeland and Zuid-Holland.

Searching for fossils at the Kaloot near Borssele. Eight species of rodents were found at this locality, mainly cold and steppe favouring species: Lemmus lemmus (norway lemming), Dicrostonyx torquatus (arctic lemming), Spermophilus sp. (ground squirrel), Microtus oeconomus (root vole). The presence of Arvicola terrestris (water vole) with undifferentiated enamel indicates an Early Weichselian and/or Saalien age.


Small mammal inventory dutch beaches: A long term project with regular updates

Another  project is making an inventory of all small mammals that can be found in deposits from the Meuse/ Scheldt delta. This often concerns material from reworked sediments found on beaches. Although this material is not anymore in stratigraphical context, it can help us date with more accuracy fossils of big mammals found on the same beaches. Surprisingly, shell and shark teeth collectors are very likely to encounter vole teeth in their sieving samples. Preliminary reports are frequently published (Dieleman, 2005; 2006a; 2006b; 2008; 2010a; 2010b; van den Hoek Ostende & Dieleman, 2010; Dieleman 2013). Material from sand dredged from the North Sea contains around fifty small mammal species (voles, other rodents and insectivores), from faunas of very different ages, varying from Holocene/ Late Pleistocene to Early Pleistocene/ Late Pliocene.



“Be surprised by a lemming!” 

Dicrostonyx torquatus (arctic lemming, halsbandlemming) from Nieuwvlietbad (beach) found by mr. Jos Billekens  


current sub-project: Small mammal inventory Maasvlakte 2 beach

At the Maasvlakte 2 beach thousands, perhaps millions of vole molars are hidden in the sand. They can be found by sieving sand or just by searching with the naked eye at the beach. In 2011 I started a survey to investigate the occurrence of small mammals at MV2.

Preliminary results

With the help of several collectors, hundreds of vole teeth were found at the Maasvlakte 2 beach. The survey continues, but the preliminary results are presented here.

At the beach, molars of different ages are found. A strong dominance of late Early Pleistocene (late Biharian) voles is proved by the abundance of the watervole Mimomys savini. A diversity of Microtus species (including Allophaiomys sp.) and Mimomys species show that the entire Biharian period is represented. The Middle Pleistocene is represented by Arvicola cantiana and by Arvicola terrestris with undifferentiated enamel. Cold climate indicators are extremely rare, two fragments of the lemming Dicrostonyx sp., whereas Lemmus has not yet been found. Late Pleistocene voles are also rare. The appearance of a few molars of Tiglian voles, representing the oldest small mammals at the beach, is remarkable.


Cooperation between professional palaeontologists and active amateurs can lead to spectacular finds, as was the case when two devoted men, Joop Boele and Louis Verhaard, independently screened boreholes for fossils, and came up with the most primitive vole species of Mimomys ever encountered in the Netherlands. Research then crosses the borders of the Netherlands to compare with material from sites elsewhere in Europe. In this project I worked together with Naturalis microvertebrate specialist dr. Lars van den Hoek Ostende, and the late dr. David Mayhew, Naturalis research associate, specialised in Late Pliocene/ Early Pleistocene voles. We published a paper on the oldest Dutch vole up till now: Mimomys hajnackensis (Mayhew et al, 2008). Mr. Boele and Mr. Verhaard pulled the record for fossil voles down with another million years to approximately 3 Ma by finding two lower first molars of M. hajnackensis in boreholes!

I therefore invite the public to come forward with any finds of voles or other small mammals from beaches and boreholes.





 Dutch Associations of Geology and Paleontology (NGV, GEA, WTKG, WPZ, KZGW, NKVP)







Available student projects

Public outreach

I give public lectures about my research activities


Mayhew, D.F., Dieleman, F.E., Slupik, A.A., Hoek Ostende, L.W. van den, Reumer, J.W.F., 2014. Small mammal assemblages from the Quaternary succession at Moriaanshoofd (Zeeland, the Netherlands) and their significance for correlating the Oosterschelde fauna. Geologie en Mijnbouw 93, pp 119-134. DOI: 10.1017/njg.

Dieleman, F.E., 2013. Overzicht van strandvondsten van woelmuizen en andere kleine zoogdieren langs de Nederlandse stranden: stand van zaken 2013. Afzettingen WTKG 01/2013; 34(4):144-172.

Slupik, A.A., Wesselingh, F.P., Mayhew, D.F., Janse, A.C., Dieleman, F.E., Van Strydonck, M., Kiden, P., Burger, A.W. & Reumer, J.W.F., 2013. The role of a proto-Schelde River in the genesis of the southwestern Netherlands, inferred from the Quaternary successions and fossils in Moriaanshoofd Borehole (Zeeland, the Netherlands). Netherlands Journal of Geosciences – Geologie en Mijnbouw 92 (1): 69-86.

Mol, D. Plicht, H. van der, Vos, J. de, Gravendeel, B., Langendoen, W., Broek, W. van den, Langeveld, B., Dieleman F.E., Reumer J., 2013. The Eurogeul area - new paleontological data of this part of the North Sea. International Conference World of Gravettian Hunters, Kraków 58-63.

Dieleman, F.E., 2012. Mimomys savini op de Kaloot, een onderzoek naar de verschillen tussen eerste bovenkaakskiezen van Mimomys savini en Mimomys pliocaenicus. Cranium 29 (1): 25-29.

Dieleman, F.E., 2011. Mimomys savini, een nieuwe soort fossiele woelrat voor de Kaloot. Voluta 17 (1): 4-14

Hoek Ostende, L.W. van den, Dieleman, F.E., 2010. Talpa Europaea van de stranden van Breskens en Ouddorp. Cranium 27 (2): 70-72.

Dieleman, F.E., 2010. De Noordzee als vindplaats van kleine zoogdieren. Cranium 27 (2): 43-48.

Dieleman, F.E., 2010. De kleine zoogdieren van het strand van de Kaloot nabij Borssele. Cranium 27 (1): 9-17.

Dieleman, F.E., 2008. De kleine zoogdieren van de Kaloot. Voluta14 (2): 3-11.


Mayhew, D.F., Dieleman, F.E., Boele, J., Verhaard L. & van den Hoek Ostende, L.W., 2008.Mimomys hajnackensis from the Pliocene of the Netherlands. Netherlands Journal of Geosciences, 87 (2): 181-188.

Dieleman, F.E., 2006b. Oproep: Muizenkiezen gezocht. Afzettingen WTKG 27:32-33.

Dieleman, F.E., 2006a. Oproep: Muizenkiezen gezocht. Voluta 12 (2): 21.

Dieleman, F.E., 2005. Muizenkiezen op het strand. Afzettingen WTKG 26:47-51.

Please contact the author when you are interested in one of the articles above and it is not available online or in the repository [Repository].