In evolutionary biology, convergent evolution is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. It is the opposite of divergent evolution, where related species evolve different traits. On a molecular level, this can happen due to random mutation unrelated to adaptive changes; see long branch attraction.

In cultural evolution, convergent evolution is the development of similar cultural adaptations to similar environmental conditions by different peoples with different ancestral cultures. An example of convergent evolution is the similar nature of the flight/wings of insects, birds, pterosaurs, and bats. All four serve the same function and are similar in structure, but each evolved independently. Some aspects of the lens of eyes also evolved independently in various animals.

Convergent evolution is similar to, but distinguishable from, the phenomena of evolutionary relay and parallel evolution. Evolutionary relay refers to independent species acquiring similar characteristics through their evolution in similar ecosystems, but not at the same time (e.g. dorsal fins of extinct ichthyosaurs and sharks). Parallel evolution occurs when two independent species evolve together at the same time in the same ecospace and acquire similar characteristics (extinct browsing-horses and extinct paleotheres). Structures that are the result of convergent evolution are called analogous structures or homoplasies; they should be contrasted with homologous structures, which have a common origin.

 

65 Million Years Ago - The Paleocene Epoch

The ancestry of dogs, though varying theories exist, can be traced as far back to the Paleocene Epoch, during the late Selandian or Thanetian age, nearly 65 million years ago, when placental land mammals originated. Miacis cognitus is considered to be the genus of carnivorous mammals that gave rise to all modern Carnivora, including the founding father of the modern dog. He is also the ancestor of the bear, wolf, jackal, coyote and fox, jackal, and hyena, to name just a few.

"Miacis"

Kingdom: Animalia | Phylum: Chordata | Subphylum: Vertebrata | Class: Mammalia | Order: Carnivoramorpha | Superfamily: Miacoidea | Family: Miacidae | Genus: Miacis

Miacids, weasel-like in form, are small, about the size of a ferret (~30cm) and roamed the North American and European continents. They are representative of the group of early carnivores that are the ancestors of modern carnivores. They have low skulls, and long, lithe bodies with long tails. The hind limbs are longer than the forelimbs, the pelvis very doglike in form and structure. Miacis had binocular vission and larger brains than those of the Creodonts, an extinct group of carnivorous mammals that were previously considered to be the ancestors of modern Carnivora, but this is no longer thought to be the case. They were slow, clumsy and inefficient and became extinct in the early Pliocene.

Miacis are well suited for an arboreal lifestyle with needle sharp claws and were probably omnivores as peaceful plant eaters or ferocious meat eaters that preyed upon smaller animals. Miacis is believed to be a den dweller that left its den for defecating/urinating to keep his area clean. They possess Carnivora type carnassials and have 44 teeth, but lack a fully ossified bony middle ear cavity. The miacids are divided into two groups: the miacines with a full complement of molars and the viverravines with a reduced number of molars and more specialized carnnassials.

 

50 Million Years Ago - The Eocene Epoch

The two main branches of the Order Carnivora arise from the Miacids: Caniformia (dogs raccoons, bears, sea lions, seals, walruses, and weasels) and Feliformia (cats, hyenas, civets, genets, and mongooses). Caniformia is the most primitive among the dog-like carnivores which includes the Pinnipeds (walruses, seals, and sea lions), known as the Arctoidea, which also includes the Ursidae (bears) and the Mustelids (weasels), Procynoids (raccoons), Mephitidae (skunks) and Ailrus (red panda). The oldest caniforms are the Miacis species Miacis cognitus, the Pseudocynodictis Hesperocyon, Cynodictis, and Amphicyonidae (Bear-dogs) such as Daphoenus.

pseudocynodictis

Order: Carnivora | Family: Canidae |

Subfamily: Hesperocyoninae | Genus: Hesperocyon

Hesperocyon canids were Boraphaginae, an extinct genus of canids and the earliest to evolve after the Caniformia-Feliformia split 42 mya. The earliest Hesperocyon were small kit fox-sized animals with supple, muscular bodies, long tails, padded feet, and resembled the modern dog. Their legs were longer than Miacis which enabled this mammal to swiftly catch its prey as they also walk on their toes (digitigrade) like modern canids. Its fifth toe would eventually become the dewclaw.

cynodictis "Dawn Dog"

Order: Carnivora | Family: Canidae |

Subfamily: Borophaginae | Genus: Cynodictis

 

Cynodictus "Dawn Dog" were Borophaginae that diverged from the Canidae family, while the Caninae lineage diverged and led to modern-day Canidae (wolves, coyotes, foxes, jackals and dogs). Cynodictis had a long muzzle and a low-slung body. It had carnassial scissor teeth for slicing chunks of meat off carcasses. While Cynodictis died out in the Oligocene Epoch through competition with the more highly evolved Bear Dog, Cynodictus is the ancesteral parent to the modern dogs of Africa, "Lycaon", and India, "Dhole"; also, the South American bush dog, "Speothos".

 

 

 

25 Million Years Ago - The Oligocene Epoch

The first split within the Caniformia begins, progressing from the Eocene epoch into the Oligocene epoch, two descendants of Miacis evolve: Hesperocyon and Amphicyon. In North America, Hersperocyon appears and never wanders to the old world. It is the first canid genus and the basis of the hesperocyonine radiation, the first of three radiations of canids:

  1. Hesperocyoninae (~40-15 mya): The most ancient and archaic group of canid. Originated and remained in North America, this group of canids became the dominate carnivores of its time, including frugivorous, bone-crushing hyena-like, and coyote-sized canids.
  2. Borophaginae (~36-2 mya): Commonly known as the hyenoid dogs, this is the largest and most diverse group of ancient canids. The Borophaginae is convined to North America during its entire existence. Species in this group span a wide spectrum of ecological niches from raccoon-like omnivores to hyena-like top predators. This subfamily became extinct shortly before the Pleistocene.
  3. Caninae (~33 mya): This group contains all of the living canids in the world. The worldwide distribution of modern canids is the result of their migrations during the late Cenozoic to the last five million years.

daphoenus "Bear Dog"

Order: Carnivora | Family: Amphicyonidae | Genus: Daphoenus

The second split was with Amphicyon, Daphoenus, more commonly known as the "Bear Dog", which later evolved into the present-day bear. Although one must trace back millions of years, it is curious to note the relationship between bear and dog from the carnivore's founding father, Miacis.

 

10 Million Years Ago - The Miocene Epoch

 

Lycaon

Borophagus

In the Miocene period, 5-24 million years ago, three descendants from Cynodictus emerged. Lycaon sired today's wild breed African dogs. Borophagus fathered the jackels and hyenas. And finally, Tomarctus stood at the head of the modern family of wolves and ultimately, dogs.

 

 

 

"Virtually wherever history has been recorded there have been dogs represented in writings and on pictographs. Evidently, the domestication of dogs and the civilization of man occurred at the same time."


 

Dogs are members of the order Carnivora, a group of mammals with origins in the Tertiary era, about fifty-five million years ago. The earliest fossils of ancestors of this order, the Miacoides, predate that distant time.

These animals varied in size, from about the length of a weasel to that of a wolf, and had the characteristic teeth of present-day carnivores.

The story of the Canidae family begins in the Northern Hemisphere during the late Eocene and early Oligocene epochs. On each side of what is now the Atlantic Ocean there lived two closely related animals: Cynodictis in Europe and Pseudocynodictis in North America.

The European animal died out in the Oligocene epoch (35 million years ago) through competition with the more highly evolved Ursidae or "Bear Dog". The North American species survived, later giving rise to what we now recognize as the dog. Pseudocynodyctis was a low-slung and very long animal with a long muzzle. Evolution led to the lengthening of its legs.

Following Pseudocynodictis in North America came Mesocyon, with a skeleton similar to that of a present-day wolf. Its descendant was Cynodesmus (early Miocene epoch, 25 million years ago) which thereafter gave rise to Tomarctus, known to have existed in the middle and late Miocene epoch.

Shortly before the beginning of the Pliocene epoch (10 million years ago) the genus Canis appeared and migrated into what is now Eurasia. Its earliest representative in the Old World, Canis cipio, was discovered in the deposits in Concud, near Teruel, in Spain. It lived about six million years ago. The genus evolved through different species up to the Canis lupus, or wolf, which dates back approximately 300,000 years.

 

The Readers Digest

Illustrated

Book of Dogs

Second Revised Edition

ISBN 0-88850-205-2   

 

Dr. Xiaoming Wang

Associate Curator of

Vertebrate Paleontology

Natural History Museum

Los Angeles, CA

 

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