The spotted hyena is remarkable for how small, not how large, its head is

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There is a notion among naturalists that the spotted hyena (Crocuta crocuta) has a massive head.

This seems to reflect a subconscious assumption that any head capable of such prodigious bone-crushing must surely be massive.

Actually, photos usually show a remarkably small head, relative to body size (https://www.gettyimages.com.au/detail/photo/spotted-hyena-in-serengeti-royalty-free-image/1028833486?adppopup=true and https://www.gettyimages.com.au/detail/photo/hyena-running-royalty-free-image/158636169?adppopup=true and https://www.gettyimages.com.au/detail/photo/animal-standing-in-grass-royalty-free-image/601799017?adppopup=true and https://www.gettyimages.com.au/detail/photo/spotted-hyena-laughing-hyena-observing-the-royalty-free-image/975235922?adppopup=true and https://www.gettyimages.com.au/detail/photo/hyena-striding-purposefully-amboseli-national-park-royalty-free-image/1174345598?adppopup=true and https://www.gettyimages.com.au/detail/photo/side-view-of-a-lioness-walking-on-grassy-field-royalty-free-image/1355343050?adppopup=true and https://www.gettyimages.com.au/detail/photo/hyena-crossing-road-royalty-free-image/1181962352?adppopup=true).

The neck of the spotted hyena certainly is both long and thick. However the head is small considering its bite force. And I suggest that this incongruity is what the spotted hyena should really be renowned for.

I have before me Skinner and Chimimba (2005), the authoritative work on the mammals of southern Africa. This has a long and detailed account of the spotted hyena.

I quote: “The head is...massive...The skull of the spotted hyena is massively built and the whole head may weigh over 3 kg.”

Now, let us look at the actual figures they cite.

The body mass of the spotted hyena in southern Africa, according to Table 229.1 in Skinner and Chimimba (2005), is an average of 65-71 kg in adult females, the larger sex. In the Kruger Park in particular, the mean figure is 65-70 kg. Let us take 68 kg, which happens to be about the same value as the mean body mass of adult males of the human species, in a population without obesity.

Expressing 3 kg as a percentage of 68 kg, I see that the relative mass of the head is about 4.4% in the spotted hyena.

Now let us compare this figure with that for the human species, which nobody would describe as having a ‘massive head’, least of all in women. The human head weighs 4.5-5kg, which is about 8% of body mass. I checked this by taking a head mass of 5 kg and a body mass of 70 kg, both for adult males of the human species. I calculated 7%.

So, females of the spotted hyena have a head about 4.5% of body mass, whereas males of the human species have a head about 7% of body mass. This comparison is particularly telling, because both species have the same body mass - if one takes the larger sex in both cases (female hyena vs male human).

This seems to reveal a lack of objectivity in Skinner and Chimimba (2005). They describe the head of the spotted hyena as massive, but their own figures indicate a head that is only two-thirds the relative mass of the human head.

So, is the idea that the spotted hyena has a massive head an assumption/exaggeration, that has affected even supposedly objective scientists?

I tested this by examining the photos below, of the heads of the two species right next to each other.

In most cases, the spotted hyena depicted has adult body mass of about 70 kg. I.e. these photos were mostly not taken in Kenya or Tanzania (where the adult body mass of the spotted hyena is about 50 kg).

And in several cases the human individuals seem rather small. By my reckoning, the head of the spotted hyena looks more, not less massive, than that of the human species.

This suggests that Skinner and Chimimba (2005) may have underrepresented the mass of the head of the spotted hyena as 3 kg, and that both species have head masses of more than 4 kg (please bear in mind that the air-filled sinus in the forehead of the hyena is, as far as I know, larger than that in the human species).

However, even with this caveat, my point is that

based on the figures they themselves cite, Skinner and Chimimba (2005) contradict their own assertion that the head of the spotted hyena has noteworthy size, and
any photo of the species will show observant naturalists that the head is not particularly massive relative to its body, for such an exceptional bone-crusher.

I suggest that the power of the jaws of the spotted hyena is owing mainly to efficiency in the bite, based on the precise location and shape of the conical premolars (https://www.youtube.com/watch?v=CDw4UHbE5Gs and https://www.gettyimages.com.au/detail/photo/laughing-hyena-royalty-free-image/154930600?adppopup=true and https://www.gettyimages.com.au/detail/photo/teeth-of-the-spotted-hyena-also-known-as-the-royalty-free-image/1225876651?adppopup=true and https://www.gettyimages.com.au/detail/photo/close-up-of-a-tired-hyena-royalty-free-image/1270581600?adppopup=true).

I.e. the jaws operate by specialised application of limited force, as opposed to gross, sheer strength.

The implication is that what is really remarkable is not how large this head is, but how small it is, for the efficacy achieved in crushing bones.

https://www.youtube.com/watch?v=TxwNfH2HrYY

https://upload.wikimedia.org/wikipedia/commons/4/42/Kevin_Richardson_with_hyenas.jpg

https://upload.wikimedia.org/wikipedia/commons/6/6a/Harar_Hyena.jpg

http://cache2.asset-cache.net/gc/106779883-spotted-hyena-called-bongo-sits-on-kevin-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=R4V%2FQay2ANwpmCZhkZDSEogdKSo3PYXpemQ0Biko14dlOvpp67oXvKnR%2FOx7I1DvwNvwMoYQakE%2BourL9kiRSw%3D%3D

http://cache3.asset-cache.net/gc/106779895-spotted-hyena-called-bongo-sits-on-kevin-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=R4V%2FQay2ANwpmCZhkZDSEi8alhpJ%2BM%2FFHdahVE5LlN4nRUbgXdqaTo9k65ShDEiBOcpEBabOT5AEkqBsEIAN9Q%3D%3D

https://i.ytimg.com/vi/5monBOLIt5E/maxresdefault.jpg

http://i.dailymail.co.uk/i/pix/2012/02/07/article-2097669-119FA9B9000005DC-841_634x368.jpg

http://cnpic.zhgpl.com/upload/201202/10/102006574.jpg

http://s6.photobucket.com/user/foxylibrarian/media/hyena.jpg.html

http://thewildlife.wbur.org/wp-content/uploads/2014/07/Glickman-Krista-hyena-love.jpg