The relation between forelimb structure and hunting methods
The brachioradialis muscle is responsible for the turning
out ability (supinate) in the forelimbs of most Carnivora (Souza et al. 2015). Due to the hunting tactics
of running after prey, species of the Canidae family have minimal muscle with some
having completely lost it (Biben, 1983).
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| Feline forelimb structure showing the placement of the Brachiordialis muscle, responsible for the supinating forelimb ability |
Early canids from the families Borophaginae and Hesperocyoninae
had morphologies suggesting they were solitary hunters (Andersson, 2005). They had
much shorter faces with larger front teeth and smaller back teeth. They were
also able to turnout their forarms unlike today’s canids (Andersson, 2005). This
was possible by having a large brachioradialis muscle near the elbow. These traits
are similar to that of current Felidae which
are predominantly lone hunters and solitary animals (Andersson, 2005). The Dingo
(Canis Lupus dingo) however, has similar forelimb flexibility to the
early canids with full movement in the wrists and the ability to open the
forelimbs wide from the shoulder. This movement allows the dingo to withstand grappling
with its prey, but also climb trees to low heights (Revil, 2013). This lets the
dingo to hunt alone and be a solitary animal until mating season (Revil, 2013).
It is unknown however, whether the dingo’s
morphology was retained through ancestors or re-evolved later (Revil, 2013).
Species of the Canidae family which are social and pack
hunters have lost the movement in their limbs. Canids such as the bush dog (Speothos venaticus) which is highly
social has evolved stiffer limb structure suited for chasing prey as a pack and
having many dogs taking down the prey (Biben, 1983). Other species
suited to running such as African wild dogs (Lycaon pictus) and greyhounds (Canis
Familiaris) have also completely
lost the brachioradialis muscle (Andersson, 2005).
 |
| Hunting techniques of the African wild dog include running after prey and attacking it as a pack. http://voices.nationalgeographic.com/2013/11/20/top-25-photographs-from-the-wilderness-18/ accessed 22/3/16 |
The crab-eating
fox (Cerdoeyon thous) is a
smaller canid with again different social behaviour unlike the solitary dingo
and packing bush dogs (Macdonald & Courtenay, 1996). The foxes stay in
small groups of between two to five members (Macdonald & Courtenay, 1996). The
hunting however is separate except in breeding season. The foxes contained some
movement in the area of the forelimb, but again compared to other Carnivorans
such as Felidae, the movement is limited (Souza et al. 2015).
Andersson, K. 2005, Were there pack-hunting canids in the
Tertiary, and how can we know? Paleobiology, 31(1):56-72
Biben, M. 1983. Comparative ontogeny of social behaviour in
three South American canids, the maned wolf, crab-eating fox and bush dog:
implications for sociality, Animal Behaviour. 31, 814-826
MACDONALD, D. W. & COURTENAY, O. 1996. Enduring social
relationships in a population of crab-eating zorros, Cevdocyon thous, in Amazonian Brazil (Carnivora, Canidae). Journal
of Zoology, London. 239, 329-355
Revil, R. 2013, pers. comm
Souza, P. D. Santos, L. M. R. P. Nogueira, D. M. P. Abidu-Figueiredo,
M. & Santos, A. L. Q. 2015 Occurrence
and morphometrics of the brachioradialis muscle in wild carnivorans (Carnivora: Caniformia, Feliformia) Zoologia
32 (1), 23-32
That’s quite remarkable! Do we see the loss of this muscle in other animals that are cursorial (adapted to running) or in other animals that are highly social (like some of the herbivores)? I’m also interested to know why crab-eating foxes are also called zorros (as in the reference list).
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