Forelimb structure and hunting

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).  

Feline forelimb structure showing the placement of the Brachiordialis
muscle, responsible for the supinating forelimb ability

https://www.studyblue.com/notes/note/n/cat-muscles-for-

quiz/deck/12882676

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).

References:

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

  

The relationship between Jaw/skull structure and hunting strategies

Canid Skull/Jaw Structure 

Ethiopian wolf hunting small mammals
http://www.gettyimages.com.au/detail/photo/ethiopian
-wolves-searching-for-food-in-a-high-res-stock-photography/95647033
accessed 15/03 

The jaw structure varies greatly among canid species (Slater et al. 2008). Their skull shape and proportions affect bite force and speed, and prey types allowing the species to evolve and fill specific niches (Slater et al. 2008). Canids with smaller prey have evolved longer but thinner skulls allowing for fast and precise hunting (Slater et al. 2008). This enables predators such as the Ethiopian wolf (Canis simensis) to be able to catch their main prey (Ashenafi et al. 2005). The wolves half evolved to pounce and reach into the dens of small rodents which make up at least 88% of their prey (Ashenafi et al. 2005).

General hunters (Slater et al. 2008) such as the black backed jackal (Canis mesomelas) have a variety of prey. These hunters’ diet ranges from sea birds in coastal areas (Avery and Avery, 1997) to carrion, antelope and grazing stock (Grafton, 1965). The Jackals have evolved skull structures that balance strength and speed to allow them to survive in environments of natural and human influenced food sources (Grafton, 1965). The jaw structure of the Jackal is shorter and broader than that of the Ethiopian wolf, thus allowing the bones to withstand and exert more pressure.

Canids that specialise in larger prey have been proven to have very broad, short jaws (Slater et al. 2008). This evolution allows large hunters like The African wild dog (Lycaon pictus) to get the maximum amount of jaw strength (Slater et al. 2008). The dogs’ preferred prey are large animals such as gazelle and impala (Hayward et al. 2006). Due to the mass and strength of the prey, the dogs must have the jaw strength to hold the prey and be able to handle and added pressure the prey exerts (Slater et al. 2008). For this reason, the wild dogs also have larger muscle structures than the other two species mentioned (Slater et al. 2008). This adds to both pressure cushioning and added bite force (Slater et al. 2008).

Jaw structure of canids varies greatly among species. This evolution over times allows the species to fit their niches with very specific diets (Slater et al. 2008).

Figure 2. Skull structure of Ethiopian wolf (j), Black backed jackal (k) and African wild dog (i).
Slater et al. accessed  14/03

Slater, G. J. Dumont, E. R. Van Valkenburgh, B. 2008. Implications of predatory specialization for cranial from and function in canids, Journal of Zoology,

Ashenafi, Z. T. Coulson, T. Sillero-Zubiri, C. Leader-Williams, N. 2005. Behaviour and Ecology of the Ethiopian Wolf (Canis simensis) in a human dominated landscape outside protected areas, Animal Conservation 8, 113–121  

AVERY, G. AVER, D. M. 1987. Prey of coastal black-backed jackal Canis mesomelas (Mammalia: Canidae) in the Skeleton Coast Park, Namibia, Journal of Zoology London. 213, 81-94

Grafton, R. N. 1965. Food of the Black-Backed Jackal: A Preliminary Report, Zoologica Africana, 1:1, 41-53,

Hayward, M.W. Obrien, J. Hofmeyr, M. Kerley, G. I. H. 2006. Prey Preferences of the African Wild Dog Lycaon pictus (Canidae: Carnivora): Ecological Requirements for Conservation. Journal of Mammalogy, 87(6):1122–1131

Canids

Canids

Canids (Canidae) are dog like creatures including wolves, jackals, coyotes, foxes, wild dogs, dingoes and dholes with a total of 13 genera and 36 species extant. They belong to the order Carnivora, placental mammals with a diet almost entirely meat (Macdonald, Zubiri. 2004). Due to their diet, Carnivora is distinguished by the possession of carnassial teeth, used to slice their prey’s flesh (Jensen, 2007). Canidae has two subfamilies being vulpini which includes the foxes and canini which includes wolves, jackals, coyotes, dholes, wild dogs and dingoes.

Figure 1, Dog skull showing predominant Carnassial teeth.
https://en.wikibooks.org/wiki/Anatomy_and_Physiology_of_Animals/The_Skeleton
accessed 9/3/2016 

Canids are from the suborder Caniformia in which there are two superfamilies Cynoidea and Arctoidea (Macdonald, Zubiri. 2004, Jensen, 2007). Canids belong to Cynoidea while Arctoidea includes Ursidae (bears), Pinnipedea (walrus) and Musteloidea (skunks, racoons and otters) (Macdonald, Zubiri. 2004). Today’s canids share a common ancestor from over 40 MYA (Jensen, 2007). Due to this common ancestor, canids share a couple of distinguishing features which have been seen in fossils of even the extinct species (Macdonald, Zubiri. 2004). One of these features is the middle ear structure which can be used to identify between other carnivore families (Jensen, 2007).

The canids inner ear has a large entotympanic bulla (large round bone which holds ear drum) and a septum between the inner ear bones. Canids have also completely lost the stapedial artery, which connects inner ear muscles in fetuses of other mammals (Macdonald, Zubiri. 2004, Jensen, 2007, Fisher, Unknown). The placement of the carotid arteries is also different to other mammals being closer to the brain (Macdonald, Zubiri. 2004, Jensen, 2007). This placement is said to lower the risk of congestion and add protection to the arteries during the hunt (Fisher, Unknown).

Figure 2. Carnivora Family Tree
http://sweetpics.site/f/felidae-family-tree.html
accessed 9/3/16

The original “canids” belonged to the subfamily Hesperocyoninae about 40MYA. This subfamily paved the way for two more subfamilies, Borophaginae and Caninae (Macdonald, Zubiri. 2004). At this stage the dentition began to evolve (Macdonald et al, 2004) which will be mentioned more in weeks to come. The extinction of the Borophaginae subfamily allowed the caninae to populate much of North America (Macdonald, Zubiri. 2004). Leptocyon was the first species of the Caninae (Macdonald et al, 2004). This species was small with an elongated jaw and extremely similar dentition to today’s canids (Macdonald et al, 2004). The Vulpini came about later and began evolving to fit the niches the Canini had left open (Macdonald et al, 2004).  The Canids spread across Europe and Africa, then with the help of humans moved into Australia becoming the world’s largest and most spread group of predators (Macdonald, Zubiri. 2004). 

References:

David W. Macdonald, Claudio Sillero-Zubiri, 2004, The Biology and Conservation of Wild Canids, Oxford

Per Jensen, 2007, The Behavioural Biology of Dogs, CABI

A.G Timbrell Fisher, A Case of Complete Absence of Both Internal Carotid Arteries, With a Preliminary Note on the Developmental History of the Stapedial Artery, Demonstrator of Anatomy and of Surgical Anatomy, P 38-46

David W. Macdonald, Claudio Sillero-Zubiri, Michael Hoffman, Status Survey and Conservation Action Plan, Canids: Foxes, Wolves, Jackals and Dogs, 2004, The World Conservation Union