Determining the Dog’s Earliest Ancestors

Ever wonder how the pet dog became the first domesticated animal? Although it may be hard to believe, what we would consider the true early ancestors[1] of man’s best friend goes all the way back to the Cretaceous–Paleogene (K–Pg) extinction, directly following the end of the dinosaurs.

Carnassial TeethIf you think about it, when examining fossils dated millions of years old, – there is no DNA to extract and consequently no biological information to gather either. So how can an animal’s earliest predecessors be determined? Paleontologists have developed a way to determine the true taxonomy of ancient fossils through morphological characteristics – meaning visual similarities specifically in the placement, size and shapes of the bones.

It has been established that the definitive distinction that links modern dogs with bones of the past is a unique set of carnassial teeth, in which the fourth upper premolar and first lower molar have sharp, knife-like edges that function together as shears – ideal for tearing at meat. In fact, the word “canine” that we use today is synonymous with a “pointed tooth used to chew on meat”.

This would be a key morphological attribute that would be used to identify fossils of all our dogs’ ancestors – and the first known family to possess such a trait would be a group of tree-climbing, weasel-like creatures known as the Miacidae that go back 62 million years ago.

Age of the Miacids

The Earth’s history following the age of the dinosaurs is known as the Cenozoic Era (an era that we are still live in today), consisting of a series of epochs[2] that each represent a segment of time where the planet experienced a drastic change in both flora and fauna.

At the very beginning of the Cenozoic Era was the Paleocene Epoch, a time when the Earth’s climate was at a much higher temperature, promoting an overgrowth of dense forestry and an ongoing humid and wet atmosphere. This became an ideal environment for small tree dwellers to thrive and it would be one of those family of arboreal creatures – the Miacidae – that would be the true first ancestor of today’s pet dog.


Not exactly what you may have pictured, the Miacids appeared more like a civet rather a dog, with an exceptionally long tail and striped fur that helped keep them camouflaged. Their front paws are more like hands with semi-opposable thumbs, and they walk with a plantigrade stance – meaning both the heel and sole of their feet fully touch the ground with each step.

What may be the most shocking attribute is their small size, weighing under 15 pounds and only a mere foot in length! Their sharp claws and small agile bodies enabled them to live amongst the treetops, only to climb down to grab a quick snack. Their meals consisted of lizards, bugs, and small shrew-like mammals.

The Miacidae survived for close to 30 million years in the North American region before finally being wiped out by larger predators that had come into the area.

Carnivora and the “Caniformia-Feliformia Split”

Caniformia / Feliformia Split The Miacidae set the stage for the future of the Carnivora Order – producing over 280 species throughout the Cenozoic Era, all possessing the distinguishable carnassial teeth that would link them all together.

Moving into the superseding Eocene Epoch, the planet would experience a sharp rise in temperature (period of the Paleocene-Eocene Thermal Maximum) followed by the start of a long cooling movement that take place over Epochs to come.

It was around this large shift in climate 42 million years ago that the Caniformia-Feliformia Split would take place; This would be a monumental division in the Carnivora that would create two distinct paths – one being that of the Family Canidae (Canids that would provide the lineage for dog-like creatures such as wolves, foxes, coyotes, jackals, and dingoes) and that of the Family Felidae (Felids that would produce cat-like creatures such as lions, tigers, panthers, lynxes, leopards, pumas, and cheetahs) – in short, separating dogs from cats.


The Hesperocyoninae were one of the earliest, if not first, subfamily of canids to emerge after the Caniformia-Feliformia split. With the environment during the first part of the Eocene still largely made up of forest, the earlier Hesperocyoninae (like the Miacids) focused more on ambush tactics from the trees rather than chasing their prey on the ground. But farther into their 30 million year existence as the Earth continued to cool down, many of the trees were dying out, and the now drier environment opened up more land for a savanna-grassland type setting.


The Hesperocyoninae began exploring life on the ground, and naturally their bodies would evolve to adapt to their new lifestyle. The Hesperocyoninae would develop longer legs and their feet became somewhat digitigrade as their body weight shifted from the heel to the toes – increasing their overall speed. They could now go after more nimble, rabbit-like prey that were previously too quick to capture.

Their overall body size had also increased to an average of 2.5 feet in length and up to a 45 pound weight. This evolved canid was now resembling more of a coyote with its tall slender build, large ears, and narrow muzzle.

Unfortunately for them, their larger structure would mean more meat was required to sustain them, and as a result of aggressive predators sharing the same environment, the Hesperocyoninae could not compete and would become extinct at the end of the Miocene Epoch, 15 million years ago.


The next subfamily of canids were the Borophaginae, hungry meat-eaters that were quick to realize that if they hunt in packs, they could go after bigger prey, and in turn have bigger meals. The Borophaginae had much bigger, burlier bodies compared to their Hesperocyon counterpart – averaging 65-100 pounds and 3.5 – 5ft in length (comparable in size to today’s wolf). When traveling in a pack, they could knock down prey simply with pure strength, even if their target was 10 times larger than themselves! They were given the nickname, “bone-crushing dogs”, as they developed strong jaw muscles that could crack open bones in order to suck the nutrients out of the marrow.


However, with this increased appetite and heightened need for meat, their hypercarnivorous diet would also be their downfall. Although becoming one of the top predators in the area, when larger mammals became harder to find, their hunger could not be satisfied and the family would eventually fade out at the end of the Pliocene Epoch.

Change in Geography “Bridges” Possibilities

Land BridgesFossils did not show many drastic variances in the evolution of the Hesperocyoninae and Borophaginae as canids were still confined to North America for the majority of their existences. It wouldn’t be until the Earth’s geography was greatly altered, subsequently creating paths that would free canids from their territorial restrictions so they could go on to explore and adapt to new environments.

One of these key geographical changes took place around 8 Ma when there was a significant drop in temperature and much of the world’s water froze over, which in turn caused the sea levels to be exceptionally low, exposing much of the ocean floor to the surface. What is now called the Beringian land bridge had amazingly bridged the gap between Siberia and Alaska, connecting the two land masses and marking a monumental step in the canid’s evolution, where they could now traverse to Eurasia (Europe and Asia regions). The Beringian land bridge would appear yet again during the most recent ice age between 20,000 and 40,000 years ago.

Another type of land bridge that would form less than 10 million years ago was the Isthmus of Panama, a narrow strip of land created by parts of the Earth’s crust that were gradually pushed upwards by two colliding tectonic plates. The isthmus ended up joining North and South America, allowing canids to move more south and explore even more territories.


Caninae: Dingo, Wolf, Jackal, Fox, Coyote
Caninae: Dingo, Wolf, Jackal, Fox, Coyote

The third and final subfamily of the Canidae is the Caninae (not too confusing, right?) They first appeared around 32 million years ago during the Oligocene Epoch and still represent the remaining 37 species of canids that exist today. The Caninae would go on to take full advantage of both the Bering Land Bridge and the Isthmus of Panama, increasing their diversity and adaptability, moreso than any of their predecessors.

Originally looking more like the modern wolf, Caninae possessed less pointed facial features, extended nasal cavity, longer premolars, bushier fur, and the development of the dewclaw of their front paws. Similar features can be seen in many of the other surviving species including foxes, coyotes, and of course – our beloved dogs.

Man Meets Dog

Ironically, even though the majority of Canidae resided in North america for most of their existence, the first domesticated canine would originate somewhere in the Eurasia region, approximately 15,000 years ago. This would be around the same time that the last ice age was coming to an end and human civilization was on the rise, leading into the beginning of the Holocene Epoch – the same time period that we are in today!

The Natufian
Natufian CultureAs one can imagine, it’s quite difficult for archaeologists to pinpoint the first human tribe that had domesticated the Caninae (most likely a type of wolf at the time), but convincing documentation does exist. One of the earliest hunter-gatherer societies labeled as the Natufian, located in the Eastern Mediterranean region, marks some of the earliest archaeological evidence for the domestication of the dog. Uncovered Natufian burial sites reveal humans buried with dogs and dogs buried with bowls nearby or a bone in their mouth, heavily suggesting a love for the animal that had passed.

Why Caninae?
You may wonder why humans chose the Caninae; Why would humans want to cohabit and share valuable meat resources with this carnivore rather than take in small herbivores that would be a lot less work to feed and care for? But it was because of their similar diets that man and dog came together; When the Caninae discovered these man-made communities, they realized it would be easier to hang around, feeding off the scraps, rather than be constantly on the move with a pack, risking their lives with each violent encounter. Soon humans and canids would form a mutually beneficial relationship, using each other’s skills to seek out prey; During this time an emotional bond would form.

Cats may started to be domesticated 9,000 years ago (a few thousand years later than dogs) probably for similar dietary reasons, although they still preserved much of their independence by being less submissive to humans. Perhaps because canids had gained their social skills from hunting in packs for so many years that they were more willing to form relationships compared to their feline counterparts.

Making their way back to North America

Native American Bond with WolfThe Neolithic Age (also known as the New Stone Age) was a period in the development of human technology, beginning about 10,000 years ago. Small groups of hunter-gatherers, along with their canines, would cross the Bering Land Bridge from Eurasia into Alaska – the same land bridge that had brought the canids to their region millions of years ago. Upon reaching North America, man and wolf would settle down in what is believed to be the first society of the Native Americans (called Paleo-Indians or Paleoamericans for back then).

Thousands of years later, wolves are highly regarded by most Native American tribes and considered to be a symbol of great courage, strength, and loyalty (often depicted in their culture’s artwork).

Selective Breeding

Left: Jacksonville Kennel Club
(Left: Greyhound Racing at Jacksonville Kennel Club, 1930’s)

Despite the fact that canids were first domesticated about 15,000 years ago, most dog breeds were developed within the last few centuries. With some level of companionship usually being a factor, humans would selectively breed certain types of dogs to make them excel at certain tasks. In the 19th century, German Shepherds were bred to help farmers with herding sheep, Bloodhounds became expert scent trackers, and Greyhounds were developed to compete in the sport of racing.

Smaller dogs were bred as a status symbol, fashion accessory, and of an attractive size that was better suited for inside smaller households.

Overall, dogs were deliberately bred to be less aggressive, more protective, and having a greater empathy towards humans. Dogs would be welcomed into the home and becoming a full-fledged family member.

But How Did Dogs Get So… Cute?

Wolf vs. DogIt’s hard to imagine that your pet chihuahua is a descendant of a bone-crushing dog or a savage pack of wolves. Today’s dog possesses much softer features that seems to melt our hearts with every glance; It’s almost as if dogs are a puppy version of the wolf… and in a way they are.

The “cuteness” phenomenon seems to have started during early domestication of the species, where the dogs’ overall appearance developed (or really retrogressed) into having more paedomorphic traits, retaining many juvenile features even though their body still reaches full sexual maturity.

It is believed that this youthful look is due to the dog’s more restful, easy-going lifestyle they have been experiencing since teaming up with us humans. As dogs are comforted by modern conveniences and no longer in that fight or flight mode that was used to survive in the wild, their fear and stress levels are lessened, drastically changing their hormonal makeup that will reshape key mental and physical developments as they mature. Certain aspects of their growth slows down, their brain size becomes smaller, and although still reaching biological adulthood, they still retain many puppy-like characteristics.

Wild vs Domesticated Fox
Right: Domesticated Foxes

(Source Irene Plyusnina/Current Biology)

Back in 1959, Russian geneticist Dmitry K. Belyaev conducted a 40-year experiment, essentially replicating the paedomorphic anomaly – only this time, with foxes. Belyaev placed wild foxes under domestic caretaking during their infancy and then bred only those that remained calm and unaggressive when exposed to a human. By the end, the foxes were found to act more like “pets” rather than feral animals – whimpering to attract attention, wagging their tails when a human was nearby, and licking one’s face when they could get close. What was more astonishing was their appearance – floppy ears, curly tails, and an overall softer bone structure.

Modern Life With Dogs

Today, there are hundreds of different dog breeds that cover an incredible array of sizes, shapes, and colors – a vast difference of genetics that has not been replicated in any other species. But more important than that, our beloved pups form a special bond with us that goes beyond explanation. Not only do we care for them like we would a child, but in return our dog serves as a source of social support and companionship, aiding in our mental health and well-being. No matter how hard your workday might have been, to come home to that wet slobbery kiss and wagging tail can fade all your worries away. They’ve truly earned the nickname, man’s best friend.


Miacidae Paleocene ~ Eocene 62 – 33 Ma
Hesperocyoninae Eocene ~ Miocene 42-15 Ma
Borophaginae Oligocene ~ Pliocene 32-2 Ma
Caninae Oligocene ~ Present 32 Ma – present


Cretaceous 66 million years ago (Age of dinosaurs)
Paleocene 66-56 million years ago
Eocene 56-34 million years ago
Oligocene 34-23 million years ago
Miocene 23-5 million years ago
Pliocene 5-2.5 million years ago
Pleistocene 25 Ma – 12,000 years ago
Holocene 12,000 years ago to present
How the Dog Became the First Domesticated Animal
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