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There is only fragmentary information about
the origins of mammals some 200 million years ago, but between 54 and 38 million years ago a unique branch of meat-eating
mammals developed. These were the carnivores, a wide variety of predators distinguished from all other meat eaters by one
shared characteristic, the possesion of carnassial teeth. Many other predators, both past and present, eat meat, but only
the carnivorous mammals have teeth that originally evolved for crushing and chewing (the four upper premolars and the first lower molars), but then adapted to cut through flesh. The evolution of the
dog can be traced by examining the fossil remains of the teeth of its extinct ancestors.
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The Creodonts were a
group ofsmall,
meat eating animals |
Creodonts
100
-50 million
years ago |
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Fossil teeth
from Miacis reveal
that this carnivore lived during
the Eocene epoch. These small
animals had spreading paws,
indicating
a probable tree-dwelling lifestyle. |
Miacis
54-38 million
years ago |
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This possible direct ancestor of the
dog family developed in what is
now
North America. This is the most ancient
species to have an inner ear anatomy,
which is characteristic
of the canine family.
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Hesperocyon
38-26 million
years ago |
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Carnivorous mammals developed
independently in different parts of
the world. Tomartcus evolved in Eurasia
and was assumed to be an ancestor of
the dog, but recent research has
questioned the link.
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Tomartcus
19 million
years ago
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By the Miocene epoch,
between 26
and 7 million years ago, 42 different
genera of dog-like canines had emerged.
Of these Leptocyon
is now thought to be
the true ancestor of the dog and all
other modern carnivores.
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Leptocyon
12 million
years ago
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At the end of the Pliocene and
beginning of the Pleistocene epochs,
2 million years ago, the foundation stock
for all modern carnivores had evolved.
The previous 42 genera of canines
had
reduced considerably to the 10 genera of
today.The largest of these is canis, of
which wolves, jackels,
the coyote and dogs
are members. |
Modern Canids
2 million
years
ago |
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The Earliest Carnivores The Ancestors of modern mammals
evolved to survive in the enviornment of their time. Most of these early mammals were herbivores, feeding solely on vegetation.
Meat eaters then evolved to live off these vegetarians. Around 50 million years ago, when the now-extinct family of meat eating
mammals called Miacis evolved, the tooth shape and distribution of present-day carnivores developed. During the following
25 million years, the increasing diversity of vegetable food led to proliferation of herbivores. This increase was mirrored
by an equally explosive expansion in the range of carnivores. Many authorities believe that the dog's most distant ancestors
lived in North America and belonged to the extinct Hesperocyon, carnivores that evolved into an enormous range of families.
Canid Features Closely related to the wolf, the dog is distantly
related to many other meat eaters. All seven families of today's carnivores - the cats (Felidae), racoons (Procyonidae), weasels
(Mustelidae), hyenas (Hyaenidae), civets and mongooses (Viverridae), bears (Ursidae), and dogs (Canidae)
- share common ancestors. Until between 20 and 10 million years ago, bears and dogs were members of the same family; as they
evolved along separate lines, the dog's modern tree began. These ancient mammals all shared a wide range of characteristics
still seen in modern canines such as the wolf, including long skulls, semi-rigid, sturdy hind legs, and lithe, loose front
legs attached to the body only by muscle. Like the wolf, they had excellent insulation fur, compact feet, large teeth developed
to catch, hold and tear, an enormous brain capacity and (judging from the bony anatomy of the skull) excellent hearing and scenting abilities. The ancestors of the dog evolved in response to climate
changes and habitat opportunities. Distant ancestors of the dog may have been solitary hunters, but around 2 million years
ago, when tropical forests and savannas gave way to open savannas and treeless steppes, herbivores gathered into herds. The
dog's ancestors either already had a social structure, or were able to develop the social relationships needed for hunting
in packs and bringing down and killing animals much larger than they. The dog's ability to form social relationships is
the basis for its success as a species.
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Physical Traits of the Wolf
Scent
Marking Social communication is important for species that hunt communally. All canines have a scent-marking
gland on the dorsal surface of the tail. The gland leaves scent wherever the tail brushes. Visual Communication All
canines have a sophisticated repertoire of body language through which way they communicate with each other. The tail's
position and the state of it's hair send explicit messages. Insulation and protection The dense, double coat of
harsh, protective hair and softer, finer inner hair provide protection from the elements. Excellent hearing Deep
within the ears, the skull has evolved to house large cavities for enhanced hearing. Large brain capacity Skull
capacity allows space for an advanced cerebral cortex necessary for cordinating group social activity. Unique Teeth Large
canine teeth developed to catch and hold prey. The lower molars and the upper premolars are adapted for shearing and cutting. Long
Skull The typical carnivore skull is long, housing extensive and strong cheek muscles, necessary for holding
on to prey, killing, and comsuming. Compact Feet In order to capture prey, canines need stability. This is provided
by soft pads, close toes and non-retracting claws. Sturdy Limbs The radius of ulna bones are "locked"
in position. This inability to rotate the forelimbs give superb stability when running. Semi-rigid hind legs The hind legs provide bursts of power and endurance. The joints are flexible,
enabling the canine to jump reasonably well.
Migration of the
Dog's Ancestors While the ancestors of today's carnivores were evolving in North America, similar
carnivore elovution was occuring in Eurasia. A group of carnivores called Amphicyon dominated Eurasia for millions of years - the Tomartcus,
a member of this family, was once thought to be an ancestor of the dog, but the Amphicyon probably died out, leaving the Hesperocyon,
a member of another family, to develop into today's carnivores. A canine (Canis davisi) evolved from this genus 10 million years ago, and migrated across the bearing straits land bridge,
radiating throughout Asia, Europe and Africa. During the next eight million years, it spread throughout Eurasia, diverging
into the ancestors of today's canines. Having completed this evolution, several of the new species returned to North America.
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