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Taxonomy of the Canids
Some authorities used to place the canids into three subfamilies: Caninae (all other living canids), Vulpinae (foxes), and Simocyoninae
(African wild dog, bush dog and dhole). However, these subfamily taxa
of the canids is highly debatable. Some taxonomists, rather, recognize
tribes in place of subfamilies. The two such recognized tribes, placed
in the subfamily Caninae, is the Tribe Vulpini, which includes the foxes of the genera Vulpes, Alopex, Urocyon, and Otocyon; and the Tribe Canini, which encompasses all other genera. The reason is because the Canidae had already been split into three subfamilies (see evolution, below).
There
has been a recent movement in the taxonomic community to "unclump" all
the South American foxes. Instead of being placed in a single genera, Dusicyon, they have been broken up into several genera based on new taxomonic systems.
Physical Appearance
Canids are medium-sized carnivores, but are more designed to be omnivorous
than felids. Because of this, canids have many adaptations that felids
do not have. Canids have more teeth in their jaw than felids. This is
necessary for an animal that eats plant matter and insects as well as
animal flesh. Many canid species' entire diet consists of insects.
Canids have 38 - 42 teeth, with the canine teeth being large but not as
sharp as felids. They have large, yet not sharp, carnassials, the
hallmark of the order carnivora. These specialized teeth help to shear
meat, however, canids tend to bolt down their food rather than shear
it. Canids, unlike felids, can move their jaws in many directions. The
skull is elongated and narrow. They also have a prominent saggital
crest (the bony plate that protrudes from the base of the skull). This
is used to anchor the powerful temporalis jaw muscles, and is bigger in
larger canid species like wolves and coyotes than in foxes, where it is
nonexistent.
Canids' body structure is characterized by a long
lithe body set on long, thin legs. They are digitigrade, meaning they
walk on the toes of their feet. In general, they have five toes on the
front foot and four on the back, the exception is the African wild dog
(Lycaon pictus), which was only four toes on the front feet. Unlike
felids, canids were built for speed and endurance. Many species often
run their prey to death. They can keep a steady gallop for a very long
distance without tiring. Canids have unretractable claws, which help it
to grip the ground while it is running.
Like many carnivores,
canids have a bony structure in their penis called a baculum. This
engorges and locks the mating pair in a copulatory "tie" for several
minutes up to an hour, depending on the species.
The fur of
canids depends on the climate in which they live. Since they live in
very diverse climates, the fur is very diverse as well. Those living in
arctic and holarctic regions have thick long fur, while those that live
in more tropical regions tend to have less dense and very short fur.
Generally, canids tend to be less vibrantly colored than felids, and
they do not have the flashy spots, rosettes, stripes and tabby markings
of their felid cousins. The exception is the African wild dog, who has
vibrant yellow, black and white markings all over its body. Typically,
canids are usually a greyish or reddish color, with lighter fur on the
underbody, face and legs, with darker markings above the eyes, around
the ears and on the back and tail. Their tail generally has thicker and
longer fur than the rest of their body. The ears are erect and usually
triangular shaped, and lined with thick lighter-colored fur.
Senses
Dogs
have very highly developed senses. Their sense of smell is the most
highly developed sense, as they rely on scent to hunt their prey as
well as communication. Hearing is next highest developed, especially in
canids that hunt mostly rodents. They can hear the soft rustle of a
mouse walking through grass as well as the high-pitched squeak of them
communicating to one another, noises that are inaudible to humans. They
also use hearing and sound to communicate with each other, and this is
important for canids that live in heavily wooded areas. Of all the
senses, eyesight is the least developed, since they do not rely on
eyesight as much as felids. However, eyesight is important for picking
up visual cues of distress from their prey as well as recognizing
communication patterns from their own kind. Canid whiskers are also
less-developed than felids, since they do not do a lot of hunting in
areas that are cramped or dark.
Social Behavior
The
larger canids are usually highly social, while smaller canids, such as
foxes, tend to be more solitary in their habits. Pack life tends to be
more suited for the larger canids, as they hunt larger prey. Pack
canids have a strict social hierarchy. Packs consist of a male and a
female, which are the only ones that breed, and their young for several
generations. Oftentimes, relatives of the parents make up the pack. The
parents, known as the alpha pair, have absolute dominance over all
members of the pack. The rest of the members of the pack are left to
determine their own rank through ritualized fighting. The rank in the
pack determines how the individual will be treated as well as the order
at feeding time. The female often represses her female offspring from
coming into heat.
Wild canids only breed once a year,
generally during a set breeding season that corresponds to availability
of food. Territoriality and aggression rise during the breeding period,
as the males compete for limited numbers of breeding females. Gestation
period ranges from 50 - 80 days, depending on the species. Litters are
variable, and can contain a single pup up to large litters of 15 or
more. Cubs are born with their eyes and ears closed, and are entirely
dependent upon their parents for food and care. They are cared for by
their parents for a very long time, and are typically weaned by 4-8
weeks. Usually, both male and female parents rear the young, with the
male helping to provide the female with protection and food.
Regardless
of social structure, all canids are territorial. They keep large home
ranges, in which they wander in search of food. Boundaries are marked
off by urine sprayed on raised objects, fecal deposits at latrines, and
secretions from specialized glands located in the anus and face.
Communication
is vocal, visual and olfactory. Canids are the most vocal carnivores,
making wide ranges of howls, barks, whines, growls, woofs, and
chuffing. They communicate using scent by marking using urine and feces
as well as possessing several scent glands, located on their face, anus
and base of the tail. The chemicals given off by these scent glands
signals a canid's sex, physical condition and sexual status. Canids in
heat give off chemicals that attract members of the opposite sex.
Canids also use a wide variety of body postures to indicate mood.
Evolution
All
the world's mammals that exist today evolved from small insectivorous
rat-like animals that began to evolve during the Cretaceous period. At
the end of the age of dinosaurs, some 65 million years ago, these
animals now had the opportunity to evolve and become more specialized.
The order Carnivora began to emerge approximately 60 million
years ago, during the Paleocene period. The primitive carnivores that
made up this group were called miacids. This common ancestor gave rise
to all dogs, bears, seals, cats, hyenas, weasels, and civets. About 48
million years ago, the suborders of Feliforma and Caniforma arose from the miacids.
Canids
originated in the late Eocene more than 40 million years ago. They are
the most ancient group of carnivores, and the first to evolve from the
miacids. The family Canidae had three major co-existing radiations, represented by the subfamilies of Caninae (modern dogs), Hesperocyoninae (ancient canids), and Borophaginae (hyena-like canines).
The subfamily Hesperocyoninae
was an archaic group of canids that originated and remained in North
America. They existed about 40 million years ago, and looked like a
cross between a fox and a weasel. They are the most ancient group, and
were the dominant carnivores of their time. They became extinct about
15 million years ago. From the Nothocyon line of the Hesperocyonids came Tomarctus, which gave rise to the Borophaginae.
The second group, the Borophaginae, existed about 34 million years ago. Like Hesperocyoinae,
they existed solely in North America. They were much larger than the
Hesperocyonids, loooking like a cross between hyenas and dogs. This
group contained the largest canid ever to exist, Epicyon haydeni,
which was about the size of a bear. Canids in this subfamily had very
large, powerful jaws. They filled a wide range of niches from
raccoon-like omnivores to the top predators. They became extinct about
2.5 million years ago.
The last group, Caninae, is the
subfamily that gave rise to all the canids alive today. They existed at
about the same time as the other two subfamilies, but did not flourish
until about 15 million years ago, when the other two subfamilies began
to wane. This group evolved solely in North America until the late
Miocene (about 7 million years ago), when they crossed the land bridge
into Asia. One of the earliest canids of this group, Eucyon, which existed between 11 - 4 mya, is considered to be the direct ancestor to all modern canids.
The
canids that crossed the land bridge became the direct ancestors for the
canids that existed there. These animals continued to cross over the
land bridge, back and forth between the two continents. This is why
there are grey wolves in both Eurasia and North America.
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