Monthly Archives: January 2016
Hyenas have long been the victims of human prejudice and superstition, from ancient tribal tales to “The Lion King”. That is a pity because it gets in the way of our perception of a group of amazing animals with incredible adaptations for their ecological niches.
Lions sometimes have a hard time defending their rightful kills against large hyena clans, but quite often it is the hyenas who lose their own prey to opportunistic lions. Such dynamics are not new, and there is every likelihood that the woodlands and prairies of the Miocene, Pliocene and Pleistocene witnessed comparable conflicts quite often.
In the Old World Plio-Pleistocene, it was the lion-sized sabertooths of the genus Homotherium who had to deal with the challenges of living next to a most impressive hyena: Pachycrocuta brevirrostris. This animal was considerably larger in its linear dimensions than the living spotted hyena, but it was also more robust, so its body mass would have been much larger.
P. breviorrostris shared all the adaptations of modern hyenas for cracking bones (massive, blunt premolar teeth, robust skull with a domed forehead) and for carrying large pieces of carcasses over long distances (long, well muscled neck, large scapula with a flat articulation for weight transmission, shortened back and hind limbs for stability). But its massive size took those adaptations to a different scale, and certainly it made the giant hyena a rival to reckon with for any competing predator.
This illustration shows Pachycrocuta cracking a large ungulate bone, and a schematic view of the anatomical features involved in this action. The massive muscles of mastication (temporalis and masseter) provided the huge force necessary to crack the bone with the premolar teeth, and the domed forehead helped to dissipate the stresses generated during the bite
But, was P. brevirrostris a scavenger and a kleptoparasite of predators such as the sabertooths, or did it kill much of its own prey? This is a good question and one to which we may never get a final answer. On one hand, its skull and dentition were adapted to process bone at a phenomenal scale, so it was clearly very well adapted to scavenging. In fact, the cutting blade of its carnassial teeth was slightly shorter than in the highly predaceous modern spotted hyena, leaving more room for the crushing section of the dentition, a detail that suggests a more scavenging lifestyle.
On the other hand, the huge body mass of P. brevirrostris made it less efficient for this animal to forage through the enormous distances required in order to come across such a dispersed resource as carrion is. More purely scavenging species, such as the modern brown and striped hyenas, are much lighter, and actually weight considerably less than the more predatory spotted hyena. And while a large body mass can be a problem for long-distance foraging, it can be an advantage for active hunting, since one or several heavy hyenas can be more effective at subduing and bringing down a large prey animal.
Whether it killed or scavenged most of its food, the fact is that Pachycrocuta had the habit of bringing lots of it back to its den sites, a habit which apparently explains the origin of several remarkable fossil sites. If nothing else, paleontologists need to be grateful to this gigantic bone cracker for its efforts to collect hundreds of bones and gather them in the places where they eventually became preserved as fossils.
A family group of P. brevirrostris gather at the den site, where the cubs play with some old bones. Such dens, when placed near seasonal lakes or waterholes, could be buried by mud during floods and the bones would be preserved as fossils
El próximo 18 de Marzo, impartiré la charla titulada “Los grandes felinos de África: evolución, pasado y presente”. Desde mi primera visita a Botswana en 1993, mis viajes a África en busca de los grandes felinos han supuesto un contrapunto y un complemento a mi trabajo de investigación sobre la anatomía, evolución y adaptaciones de estos animales. Pero a lo largo de estos años también he tenido ocasión de estudiar en diversos museos los restos fósiles de los félidos extintos de ese continente. En esta charla hago un rápido repaso a la historia evolutiva de los félidos en África, mostrando algunas de las especies más sombrosas que allí han habitado, así como unos breves apuntes de mis observaciones más sorprendentes de los leones, leopardos y guepardos en su ambiente. Finalmente proyectaremos en primicia mi documental “Belleza Salvaje: la visión de un artista de los grandes felinos africanos”.
La conferencia será en el marco del Gabinete de Historia Natural, un espacio de encuentro para todos los aspectos de la naturaleza en el centro de Madrid.
Lugar: Calle Victoria, 9. Madrid.
Entrada: 5 Euros hasta completar aforo.
As we have seen in previous posts, the Miocene was a time of gigantic hyenas and hyena-like predators. But more than that, it was a time of hyaenid diversity. So, members of the hyaenid family occupied different ecological niches, and we talk of the “civet-like”, “mongoose-like” and the ”dog-like” hyaenas, besides the more familiar “bone crackers”.
Giant bone-crackers like Pachycrocuta, for instance, were no doubt spectacular animals, but my personal favorite are the dog-like hyenas. Comparable in build and body mass to today’s coyotes and wolves, these species combined their elegant, gracile skeletons with a “multipurpose” dentition that allowed them to take a variety of middle sized prey which they would consume to the last bone, but they also could search far and wide for any carcass in the landscape, scavenging both in an opportunistic and in a more determined way.
Years ago, during my visit to Hezheng in China I was fortunate to study first-hand an amazing sample of Hyaenictitherium fossils, including many postcranial bones that gave me a much clearer idea than I had before of the body proportions of these animals.
Finally, here is the reconstructed life appearance of Hyaenictitherium, an animal that would have the approximate size of a modern coyote. The coat pattern is broadly based on that of modern hyaenids, especially that of the striped hyena and the aardwolf, but some reference to viverrids is also made
Hyaenictitherium wongii and similar species somehow filled in the Old World the niches that the true dogs were occupying in North America at about the same time. With time, some lineages of dog-like hyaenids evolved into the “hunting hyenas” of the Pliocene, apparently the only hyaenids that eventually made it to the New World… but that is a different story!
During my visit to the amazing fossil sites and Paleontology Museum of Hezheng province in China I had the opportunity to study first-hand a whole range of beautiful carnivore fossils. Among the best preserved of them were several skulls of the Miocene hyenid Adcrocuta eximia. As I mentioned in a previous post, Adcrocuta took the place of the much larger “monster-hyena”, Dinocrocuta in the Baodean environments in China, broadly comparable in age to the Turolian of Europe.
Here is one of the admirably well preserved skulls of Adcrocuta on display at the Hezheng museum of Paleontology
Unlike Dinocrocuta, Adcrocuta was a true hyena, and its size and proportions look far more familiar to a modern observer. The Hezheng skulls define the shape of the animal´s head admirably well, and allowed me to prepare a series of quick sketches of its possible life appearance. These are just impressions, but to me they are enough to get a glimpse of Adcrocuta as a lively and efficient predator and scavenger. It was the inseparable rival of Amphimachairodus in all of Eurasia, from Spain to China, but for some reason, and unlike the sabertooth, it never made it to the New World. One of the many mysteries of hyenid evolution.
It was once a popular notion to see Miocene hyenas as mere scavengers depending for their livelihood on the kills of the sabertooths. But just as we now know that modern spotted hyenas are efficient predators as well as scavengers, so our view of their fossil relatives has become more complex. The fossil record is giving more insights about these animals, and about Adcrocuta in particular. We shall see more about t in future posts!
More than a decade ago I made a reconstruction of the head of Dinocrocuta for the book “Mammoths, sabertooths and Hominids”. Back then I had not seen a single postcranial bone of the animal, but its head was impressive enough to set it apart from any other carnivore.
The skull is enormous, and yet it seems to provide barely enough room for the outsized cheek teeth. And that visual impression is well founded: if we compare the tooth row of Dinocrocuta with that of a more “typical” carnivore, such as the wolf, we notice that the premolars have become huge and they have pushed the carnassial back, farther back than the orbit. In comparison, the carnassial of the wolf is actually ahead of the orbit. As the emphasis became so strong on the function of the premolars, the molars behind the carnassials (still well developed in the wolf) became reduced or eliminated, there was simply no room for them!
In comparison, the carnassials of the wolf, seen below, are in a much more anterior or rostral position, well ahead of the orbits, and unlike the case of Dinocrocuta, there are still several sizeable molars behind them.
The functional reason for these transformations in the dentition of Dinocrocuta is clear: just as in the true hyenas, the premolars are the bone-crushing teeth in these animals, and in order for them to exert the greatest force on the bitten object, they need to be as close as possible to the articulation between the skull and the mandible, so the whole premolar row is pushed back.
The result is a skull desing that parallels the features of bone-cracking hyenas, as has been confirmed by a Finite Element Analysis of CT Scans of the fossils (see the paper here: http://onlinelibrary.wiley.com/doi/10.1111/j.1095-8312.2008.01095.x/abstract). But just like modern spotted hyenas the animal was also well prepared to take its own prey, thanks to its powerful canines and incisors. This is confirmed by evidence provided by one of the victims of this fearsome predator. Effectively, a skull of a Miocene rhino of the genus Chilotherium from China bears canine marks that fit nicely with the size and shape of the canines of Dinocrocuta, which also happens to be present in the same fossil site (see the paper here: http://link.springer.com/article/10.1007/s11434-010-3031-9#/page-1). The rhino, however, managed to escape that particular attack, and the bone shows evidence of healing; a rare example of an animal that got up close and personal with Dinocrocuta and managed to escape with its life!
Some 8 million years ago, the plains of central China were home to an incredible diversity of wildlife. Herds of antelopes, rhinos, three-toed horses and giraffe-relatives browsed and grazed in the open woodlands and prairies. The imposing sabertooth Amphimachairodus was very much in evidence and could hunt many of those herbivores, but it was not the uncontested ruling predator. There was one monstrous carnivore around that could easily displace the sabertooth from its rightful kills, a creature that we now call Dinocrocuta.
Dinocrocuta was a hyena-like predator, and the similarities made early scholars believe that it belonged in the same zoological family as modern hyenas. But more detailed studies have shown that it actually belonged in a related but separate family, the Percrocutidae, and the remarkable resemblance to modern hyenas is largely the result of convergent evolution. Like the true hyenas, percrocutids evolved adaptations for cracking bones, developing massive premolar teeth and a robust skull with a strikingly arched forehead. But Dinocrocuta took these adaptations to a truly massive scale. The largest living spotted hyenas can weight around 80 kilos, already imposing, but Dinocrocuta doubled and maybe even tripled that mass.
During a trip to China a few years ago I was privileged to study first-hand an incredible collection of Dinocrocuta fossils. It is impressive enough to see pictures of the skull of this animal, knowing that it measures about 40 centimeters in lenght. Seeing massive skull after skull in front of your eyes is a different thing. But seeing a partial skeleton just blows your mind.
Here is a picture of a skull of Dinocrocuta gigantea on exhibit at the Museum of Paleontology in Hezheng, China. This is just one of many such skulls housed in the museum’s collections
As a result of those observations I created a preliminary reconstruction of Dinocrocuta which, for the first time, brought it to life in my mind’s eye as a complete animal.
The resulting picture is that of a somewhat hyena-like animal, but the head is absolutely and relatively far more massive. The combination of a huge body mass, a massive dentition with powerful canines and crushing premolars, and a skeleton well adapted for efficient locomotion on land, meant that this animal could cover large distances in search of carrion, or of its own prey, and that it could evict any other predator from its kill -except, perhaps, another Dinocrocuta!.
In the faunas of the Hezheng basin, Dinocrocuta is the dominant large carnivore in the Bahean-aged sediments, broadly comparable to the Vallesian of Europe with an age estimate of between 11 and 7 million years. Afterwards, with the advent of the Baodean age, it becomes very rare or extinct, its place taken by the much smaller Adcrocuta, a true hyaenid very similar in size and adaptations to the modern spotted hyena. And then Amphimachairodus becomes a much more common fossil occurrence, probably reflecting in part its real dominance in the habitat. After all, dealing with the competiton of Adcrocuta would be more or less like dealing with spotted hyenas for a lion: largely a matter of numbers. But Dinocrocuta was a different matter; trying to stop it from stealing your kill would be like trying to stand in the way of a speeding freight train. And Amphimachairodus was probably wiser than taking such risks.
It is really hard to imagine why such an imposing creature would go extinct and leave its place to the much more modest Adcrocuta. As more fossils of Dinocrocuta are discovered we can expect to see detailed studies that will reveal more and more of its paleobiology, and hopefully we will come closer to understanding the mystery of its final demise.