Dogs vs Hyenas

I've always been fascinated in the paleontological record with the stories of dynastic conflict. Y'know, the situations in which two separate animal families compete for the same niche over time. This is one of the main reasons that I find the Triassic so fascinating. In spite of the lack of big charismatic megafauna like the remainder of the Mesozoic gives us in the form of all of the famous dinosaurs, in some ways the Triassic is a more compelling story. Therapsids vs. thecodonts. Thecodonts themselves giving way to the uprising of the dinosaurs. And then the Triassic is bracketed on either end by mass extinctions. The first one, the Permian Extinction event was more about wiping the slate fairly clean and then dynasties struggling to form in a vacuum. The second one was merely one dynasty losing out and passing the baton to another. 

One dynastic struggle in the paleontological record that's a little closer to home is, as the subject line says, the dog vs hyena families. Both competed for the role of cursorial pack-hunting predators, most at home on savannas or even open grasslands, but often widely distributed in various ecosystems. In this case, both worked on their best models in isolation; the cradle of the dog family was North America, while the cradle of the hyenas was the Old World. We think today of hyenas as being an African animal, since that's almost exclusively where they live now (with one species still extant in the Middle East and India, but their origin was most likely in Eurasia, and up through the Ice Age, they roamed the northern European mammoth steppes from the Iberian peninsula to Siberia.

Before we get too far in to this, let's be clear about something. Hyenas are not scavengers, or at least are certainly not obligate scavengers, as they are often described. They are highly successful pack hunters. In reality, they are often bullied away by the much larger lions from their own kills, and then have to wait around for the lions to finish so that they can eat the scraps of what they originally killed in the first place. Because both are often largely nocturnal, these interactions weren't witnessed very often, and the erroneous assumption that hyenas just followed along eating lions' kills was perpetuated. Because the hyenas also have the capability to process much more of the carcass than most other predators, with their very strong bone-cracking teeth and jaws, this was seen as an adaptation towards scavenging in particular. In reality, that adaptation has nothing to do with scavenging, although it comes in useful when you're left without best cuts of your own kills. But its also important to note that many types of hyenas over the years have not had this adaptation at all, and many types of dogs have. In fact, the most extreme example of this adaptation is not present in a hyena, but in the Pliocine dog Borophagus diversidens. However, many paleontologists have pointed out that there is no reason to believe that Borophagus was an obligate scavenger; it was most likely one of the top predators of its age.

Dogs come in three broad genetic varieties, the early hesperocyons which were probably ancestral to the other two groups, the borophagines, which had the hyena-like jaws and skulls, and of course, modern dogs, which includes wolves, coyotes, jackals, foxes, and dogs, as well as a few other isolates like the dhole and the raccoon dog. Like I said, the borophagines had a trend towards more powerful "hyena-like" jaws and skulls, and they started waning as the climate purportedly changed to favor more open terrain. This suggests that they may not have been as cursorial as modern species, and may have needed the cover of bush or woods to sneak up on and ambush their prey much moreso than modern wolves or hyenas do. If so, that would have put them in competition with great cats once they arrived from Asia. Being squeezed between cats for ambush predator roles and modern canines for cursorial hunter roles, their importance in the megafaunal assemblages gradually faded over millions of years, with the last of them dying out near the Pliocene-Pleistocene boundary.

Hyenas on the other hand, had two main lineages. The so-called "dog-like" lineage did not develop bone-cracking jaws at all. Only one such representative still exists, the aardwolf, and it has developed a more unique niche as a termite eater. However, this lineage was once much more diverse and successful, and even put out a challenge to the dogs, especially in the form of Chasmoporthetes, the "running hyena" or "hunting hyena." As Borophagus mimicked the morphology of hyenas within the dog-family, Chasmoporthetes mimicked what we consider the standard morphology of dog-like animals in some ways, although some specialists are quick to point out that it actually more resembles a cheetah than a dog, and may have lived more like those animals than like a wolf. Chasmo actually "invaded" the dog territory, and became widespread in North America for a time, living alongside Borophagus during the Blancan and Irvingtonian ages that preceded the more classic "Ice Age" Rancholabrean age. While this was a brave foray into enemy territory, it ultimately wasn't successful, and if Chasmo was more cheetah-like than dog-like, it probably was outcompeted eventually by the actual American "cheetah", Miracinonyx. The illustration below is a small pack of these animals chasing a white-tailed deer during the Pliocene.

Meanwhile, the dog invaders who crossed into enemy territory in the Old World were more successful, although they were held in check for a time. During glacial maximums in particular, much of the fresh water that we take for granted was locked up in the ice, and the continental climates were drier. This means that vast territories of northern Eurasia that we think of as covered in boreal forests today would have been cold open grassland or tundra. And this was the haunt of vast numbers of cave hyenas, a subspecies of today's spotted hyena that was considerably larger than the African group today. But invading dogs found niches; wolves haunted the more enclosed, wooded areas, various jackals mimicked the coyotes of their North American homeland as predators of small creatures as well as scavengers, and foxes were solitary, smaller hunters. As the ice retreated in just the last few thousand years or so, forests grew in size and grasslands shrank. The vast herds of grassland-dwelling animals gave way to woodland dwelling animals, and there was a shift in the megafauna herbivores. Whether it was a change in environment, a change in prey animals, or even head-to-head competition for caves and prey with people, the cave hyenas died out, leaving only their African (and middle-eastern) smaller relative to hold down the fort for the hyena dynasties, and wolves in particular took much of their place in the Old World. Curiously, wolves also invaded North America; while the dog-family was a North American native family, wolves specifically developed in the Old World and replaced the dominant large dogs in the New World, the "dire wolves" only in relatively recent years. Oddly, since we think of Africa as where the hyena dominates this niche over dog varieties, the wolf-like dog lineage is believed to have originated in Africa, and its greatest diversity is still to be found there with various types of jackals, the Ethiopian "wolf" and the Cape hunting dogs all present; although never in dominant apex predator roles.

Curiously, the "dire wolf" is now known to not be as closely related to the wolf as we once thought, due to some genetic studies done in the last year or two. Some specialists say that the dire wolf also featured bone-cracking teeth and jaws, although not as highly developed as in borophagines or hyenas. However, some specialists say the opposite, that if anything, modern wolves would have an easier time cracking bones than the dire wolf. As the dire wolf faded to be replaced by the gray wolf returning to its homeland from the Old World, significant changes in the ecology and herbivorous megafauna are believed to have occurred as well, which probably contributed to the success of the one over the other.

In any case, the modern wolf-like dogs, including jackals and coyotes, as well as the more solitary foxes, were the eventual winners, at least so far, in this dynastic struggle. The hyenas are still around, obviously, and relatively successful in Africa at least, but they've ceded much of their non-African territory to the dogs. And while one can say that in the modern environment wolves are often threatened by human activity, coyotes and jackals are still present; I've seen coyotes in urban environments, fer cryin' out loud, where they seem to thrive and resist efforts to control their numbers. And, of course, we can't forget the success of the lineages of wolf-like dogs that actually became the domestic dog.