The Evolution of the Dog

Dogs are arguably the most beloved animals alive today. Animals such as wolves are revered for their power and awe, foxes are well known throughout the world as being quick-witted and intelligent, and of course we can't forget the domestic dogs, dubbed by many as man's best friend. Just like with cats, dogs have a long history of evolution in the fossil record. Dogs are part of an order of mammals known as Carnivora, an order that evolved shortly after the death of the dinosaurs. These animals are all characterized by the presence of carnassial teeth in their jaws Around 50 million years ago, the carnivorans saw their first major split, that being the divergence of the families containing cats and their relatives, filiformia, and the family containing dogs and their relatives, caniformia. The caniforms distinguished themselves from filiforms by generally walking with their toes flat on the ground and possessing longer jaws with fewer teeth. This can be seen in caniforms such as bears, raccoons, and of course dogs. Roughly 40 million years ago, the group containing dogs split off from the one that contained all other caniforms. This group was known as Canidae. Canids, compared to other caniforms, had several new adaptations that helped them adjust to the changing world they found themselves in. As the planet began to go through a period of cooling, the once dense forests that covered Eocene Earth began to diminish, being replaced by open grasslands of the Oligocene. This environment favored animals that were able to chase down their prey. One of the evolutionary advantages found even in the earliest canids were longer legs that helped them lead a more cursorial or running centric lifestyle. The very first canid was an animal known as Hesperocyan, evolving roughly 42 million years ago in North America. Canidae can be broken up into three subfamilies that all evolved close together. These are the Hesperocyaninae, the Borophaginae, and the Caninae. Hesperocyaninae was the first subfamily to have evolved in the Eocene, with Hesperocyan being part of this group. Hesperocyan had a long, slender appearance that resembled a weasel or a civet. It had a flexible body and tail, and could have also been arboreal. This animal likely fed on a variety of smaller creatures, but it may have also been an omnivore, occasionally feeding on plant matter. As the Cenozoic progressed, members of Hesperocyaninae retained the general appearance of Hesperocyan, such as with the Oligocene gene as Mesocyan, which lived in western United States. And while many of the Hesperocyaninids of the later Oligocene and Miocene also looked similar to Hesperocyan, some such as Anhydrocyan had deep, powerful jaws that were capable of crushing bones. Unlike their earlier Eocene ancestors, these animals were most certainly solely carnivores. But despite these new predatory features, these were among the last members of Hesperocyaninae, and the subfamily would later go extinct during the Middle Miocene. While bone-crushing abilities were found only in the latest members of Hesperocyaninae, it was a key characteristic found throughout the second subfamily of Canidae, the Borophaginae. The earliest members, such as Archaeocyan and Otarocyan, had dentition that indicated a more carnivorous lifestyle compared to Hesperocyan, which lived during the same time. As this subfamily evolved, these carnivorous tendencies became even more pronounced. Their jaws became larger and far stronger, plenty of space for muscle insertions to amplify their bite force. Bone-crushing was a useful tool not only for tackling live prey, but also in scavenging. Borophagines could crack open bones and extract the nutritious marrow inside. While dogs today, such as wolves, are potent and powerful predators, many of these bone-crushers dwarfed them in size. Some genera, such as Epicyon, reached the size of a bear, and could single-handedly tackle larger prey such as camels, horses, and even mammoths. Despite pursuit predation being common within Canidae, many of these larger Borophagines were thought to have ambushed their prey and overpowered them with brute force. However, this style of attack may have led to the group's eventual downfall. There are several reasons for why the Borophagines went extinct during the early Pleistocene, but one prominent one is the arrival of cats providing competition. Cats were much more well-versed in ambush predation, and this would have proved troublesome for these bone-crushing dogs. Additionally, the larger prey that the members of Borophaginae depended on began to see a decline during the Pleistocene, leaving only the smaller, faster-moving prey that would have been able to more easily escape these predators. With the death of the last Borophagines, only one Canid subfamily remained. That was the Canidae. But before we learn more about them, let's hear a word from our sponsors. Today's video is sponsored by Brilliant. Have you ever wanted to learn more about subjects in science, technology, and mathematics, but found it either incredibly overwhelming to dip your toes in, or too boring or dry to be able to learn? If this problem applies to you, then Brilliant offers a unique solution that'll help you get into learning STEM. Brilliant offers a variety of courses in many different science and tech-based fields. From mathematics, to physics, to computer science, Brilliant offers the resources that you need to get a better grasp on numerous different topics in STEM. 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This omnivorous genus evolved in North America a little over 30 million years ago and contained many different small dog species. This includes Leptocyan delicatus, the smallest wild canid that ever lived. This canid led to two main branches of Caninae, those being the Vulpini and the Canini. Vulpini contains what are known as the fox-like canines. It includes the most basal canine that's alive today that can be found under the genus Orocyon, which contains both the gray fox found throughout North America and the island fox found on the islands off the coast of California. This genus first evolved during the Miocene around 10.3 million years ago, with the gray fox later evolving around 3.6 million years ago in the mid-Pliocene. Interestingly enough, Orocyon also had a sister lineage, Metalopex, that evolved at around the same time and likely had a similar appearance, though this genus died around 5 million years ago. Descendants of gray foxes that migrated to the nearby islands were thought to have later evolved into the island fox, which ended up becoming smaller due to island dwarfism. Despite the name, these animals are not actually quote-unquote true foxes, those belong to a separate group. The gray fox is notable for being one of the only two canids to be able to climb trees using its hooked claws. The only other dog with climbing abilities today is the closely related raccoon dog, or Tanuki, under the genus Nycterudes. As the name suggests, this canid strongly resembles a raccoon in appearance, to the point where it's often mistaken as such. You might recognize it as a more advanced version of the raccoon suit from Super Mario Bros. 3. For some reason in Japanese culture, these dogs are also depicted as having very big ta- While the raccoon dog is typically associated with Japan, this genus actually evolved in Miocene China, with some extinct species even being found in Africa. This dog, alongside the bat-eared fox under the genus Otocyon, are argued by many to be the next closest relatives to the gray foxes, and are also said to be the most basal members of Alpini. This group is also where the true foxes belong to, all falling under the genus Vulpes. This contains everything from the red fox to the arctic fox to the tiny fennec fox. Compared to the gray foxes and other canids, these animals were known to have more streamlined bodies with flatter skulls and longer, bushy tails. While Vulpini as a whole was thought to have evolved in North America, with animals closely related to the gray foxes, the earliest fossil species of Vulpes, Vulpes rafotei, was found in the late Miocene of Chad. This suggests an African origin for foxes, with other early species such as Vulpes hasani also being found on the continent. 4. Canini is the second main group of modern canids, with the first member of this group being reported to be Leptocyon. Leptocyon then led to two sister groups. One of these is which contains the South American canids. That name is really hard to say multiple times during a script, so I'll call them by another title they've been given, the Zoros. Zoros can be broken further into another two groupings which seem to have split around 6 million years ago during the Miocene of North America. The first of these contains the bush dog, maned wolf, as well as the Falkland Islands wolf, which went extinct in 1876. On the subject of extinct dogs, this branch also includes the genera Theuradictus and Protocyon, which also went extinct relatively recently, around 5,000 and 12,000 years ago respectively. The second branch of the Zoros contains the genus Lycolopex, which consists of multiple different smaller canines that are once again called foxes, even though the true foxes are under the Vulpes genus. The second branch also includes the crab-eating fox, as well as the short-eared dog, which is a really cool canine species for me just because of how long its body is. There's evidence present that supports the fact that most of these genera evolved before the formation of the Panama Isthmus around 3 million years ago during the Pliocene. Following this event, these dogs would go from Central America through the connecting land bridge, where they'd then find new homes in South America, where most of them can be found today. Finally, let's address the final group of dogs for today's video, the sister group to the Zoros known as the Canina, which also branched off from Leptocyon. The most basal members of Canina are the side-striped and black-backed jackal. Similar to the true foxes, the other members of Canina saw their evolutionary origins in Africa. These include the African wild dog, the Dole, as well as the genus Canis. Canis contains everything from the golden jackal, coyotes, the Ethiopian wolf, and basically all wolves in general. Real quick, I'd like to take a minute to address one particular canid of interest within Canina that's arguably the most famous of all prehistoric dogs, the direwolf. For a long time, it was thought that the direwolf was a larger extinct relative of our modern wolves, falling under the genus Canis as well. As recently as 2021, however, DNA studies seem to be showing evidence pointing to a different story for these animals. On one hand, we have the long-standing idea that due to similarities in morphology between the direwolf and the wolf, the two animals are closely related. However, this new DNA evidence-backed theory states that the direwolf is actually not closely related to the wolf at all. Instead, proponents of this idea place the direwolf in its own genus, Enosion, near the base of Canini, representing a branch even more basal to the subtree than the side-striped and black-backed jackals we've mentioned before. Regardless of which theory you believe to be correct, I figure it was worth bringing up here. At long last, we get to the last canine we'll discuss in today's video, that being the domesticated dog. This animal is a direct descendant of the grey wolf, Canis lupus, that was domesticated by humans as far back as 40,000 years ago. The subject of dog domestication is a topic that deserves its own video. What is worth mentioning, however, is the variety of different forms the dog has taken throughout its history with humans. Although they're all part of one species, Canis familiaris or Canis lupus familiaris if you consider dogs a subspecies of the grey wolf, they can be as big as a Great Dane, to as small as a Chihuahua, to as goofy looking as a pug, it really goes to show how far the limits of morphology can be stretched within a single species. Dogs have had a long and storied evolutionary history, but even if you ignore that, dogs are still very special to many people around the world, and many dogs are very, very cute.