There are eight species of Ursidae family which include the brown bears, polar bears, American black bears, Asian black bears, sun ears, sloth bears, spectacled bears and the Giant Panda. Out of these the brown bear, polar bear and panda are probably the most well-known and easily identified. This month I have chosen to look at the Polar bear (Ursus maritime) – mainly because I think that they are beautiful and powerful animals who are struggling at the moment due to climate change.
Polar bears live in the Arctic and survive these harsh conditions by eating seals, although they are known to wander into areas where humans live to scavenge food. They are the most carnivorous of the bear family which their dentition reflects. They have large canine teeth which can reach up to 5cm in length and elongated and slightly hooked. In addition to the canines like other carnivores the polar bear has carnassial teeth but which are smaller in size. The dentition of this bear is designed for crushing food as well as grabbing and holding on to prey rather than grinding food, such as the brown. Therefore the dental formula for the polar bear is I: 3/3 C: 1/1 PM: 2-4/2-4 M: 2/3.
The bite force for a polar bear is relatively low compared to their body size as their prey is usually quickly killed and poses little danger to them. However, they do have a strong jaw in order to hold the prey. This strength in the jaw is evident on the skull by the presence of a sagittal crest. Unlike the crest of the gorilla, seen in last month’s skull, this site for muscle attachment is not for grinding food but for gripping and ripping. As well as the sagittal crest an occipital crest can be seen at the back of the skull. This is an attachment site for the muscle and ligaments which hold up the head of the bear. These muscles help to hold onto struggling prey and to drag the carcass to feed on.
The overall skull is large for a polar bears body size and is more elongated when compared to a brown bear. This narrowing can be advantageous when accessing birth liars and breathing holes when pursuing prey. The length of the skull is also longer due to the ability to smell prey over a large home range and therefore results in a large olfactory bulb in the brain. The eyes face forward, providing good binocular vision. It is unclear how good their sight is but they can clearly see in both light and dark, and combined with their excellent sense of smell, makes them effective predators. There are also turbinate bones present in the nasal cavity of the skull which helps to warm inhaled air to protect from the cold.
Overall the polar bear’s skull is robust and strong, built for strength and force and well suited to the environment and the ability to locate and catch prey. They are incredible and powerful animals and I look forward to do some research into their evolution and morphological adaptations.
For a little insight into the evolution of the polar bear read this article by Lindqvist et al. (2010), which I have summerised in my page. I have also looked at the bio-mechanics of the skull compared to a brown bear in an article by Slater et al. (2010).
Polar Bears: A Complete Guide to Their Biology and Behavior By Andrew E. Derocher
Appearance/Morphology of the neck and head by Dr Debra Bourne MA VetMB PhD MRCVS