Gnaw, you are not going to believe this Beaver!

Upper incisor teeth of the Beaver, Castor fiber, Thames river gravel, Boveney
(NHM.285-2016)

The Eurasian Beaver (Castor Fiber), part of the Rodentia order (Rodents), is a large, semi-aquatic mammal[1]. Unlike their relatives, mice and rats, beavers predominantly live in freshwater systems such as rivers, streams, irrigation ditches, lakes and swamps[2]. As they build their homes out of trees, shrubbery and mud, living near substantial woodlands is key to the survival of the Eurasian beaver; their prime environments are freshwater habitats surrounded by woodlands2.

A useful adaptation of beavers is the ability to continuously grow their teeth. Yes, that’s right – their teeth never stop growing! The near constant use of beavers’ teeth to gnaw branches and sticks wears them down considerably[3]. By continuously growing their teeth, beavers can continue their homemaking ways for their entire life!

This adaptation is apparent when their teeth are compared to other mammals. The beaver tooth in Figure 1 shows a continuous incisor which extends beyond the upper jaw. In comparison, the canine teeth of the Brown Bear (Ursus Deningeri) are rooted (See Figure 2)[4] This means the teeth do not continue to grow when they reach maturity.

If you have ever seen a beaver in the wild, or even a photograph of one (see below) you may have noticed that they have very orange teeth. No, this is not because they have poor dental hygiene, but rather another adaptation to deal with the harsh materials that the beavers gnaw on. The orange tinge on their teeth is a layer of iron minerals [5]. This ‘extra’ layer on their incisors act as a shield and protects the interior of the teeth from erosion from the abrasive foods and materials beavers gnaw on. If you look at Figure 1, you can see how the iron mineral layer is situated at the front of the incisor, like a shield.

Beaver with orange incisors on display. Photographer: Judith Lehmberg[6]

When you are next able to visit the Natural History Museum make sure you look out for these specimens of beaver and bear teeth!

By Anjali Dhunna, Gallery Steward


Notes and references:

[1] Campbell-Palmer, R., Gaywood, M., Robinson, S. and Jones, S. (2016) Trial re-introduction of the Eurasian beaver after an absence of 400 years to Scotland, UK. IUCN Global Re-Introduction Perspectives: 2016

[2] Batbold, J, Batsaikhan, N., Shar, S., Hutterer, R., Kryštufek, B., Yigit, N., Mitsain, G. & Palomo, L. 2016. Castor fiber (errata version published in 2017). The IUCN Red List of Threatened Species 2016: e.T4007A115067136. https://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T4007A22188115.en. Downloaded on 18 October 2020.

[3] https://www.dentistrywithaheart.com/blog/the-remarkable-reasons-beavers-can-chew-down-trees-with-their-teeth/ Contemporary Dentistry. 21/07/2020 (Accessed on: 18/10/2020 15:38)

[4] https://etoncollegecollections.wordpress.com/2020/09/27/the-bear-necessities/#more-2091 Anjali Dhunna. 27/09/2020 (Accessed on: 18/10/2020 16:14)

[5] Optimized biological tools: ultrastructure of rodent and bat teeth compared to human teeth

Luebke Alwina, Loza Kateryna, Prymak Oleg, Dammann Philip, FabritiusHelge Otto, and EppleMatthias

Bioinspired, Biomimetic and Nanobiomaterials 2019 8:4, 247-253

[6] https://www.cbsnews.com/news/nature-up-close-beavers-the-master-engineers/ ‘Sunday Morning’. 07/09/2020 (Accessed on: 18/10/2020 16:19)

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