On the track of Smilodon, at last!

A couple of the earliest posts in this blog were devoted to the scanty record of cat fossil footprints, and in one of them I regretted the absence of any recognizable tracks of Smilodon. That was indeed an important hole in our knowledge because some specialists have long hypothesized that Smilodon would be a plantigrade cat. In fact, several kinds of sabertooh cats had features in their limb anatomy that were interpreted at some point as indicative of a plantigrade posture. Such features were present, for instance, in the skeleton of Homotherium, and back in the 1960s the famous paleontologist Bjorn Kurtén hypothesized that this animal walked on plantigrade hindlimbs. But, what does that really mean in terms of the locomotion an appearance of the living animal? Well, if Homotherium were plantigrade then its rump would be much lower, since the hindlimbs lost a whole segment (the metapodials) in height, and the part of the leg that rested on the ground would be proportionally much longer. The animal’s stride would become much shorter, and its gait, ungainly. One of the clearest ways to show the implications of that hypohesis is to create a detailed skeletal reconstruction of the animal in such a posture and compare it with the digitigrade alternative. I did such an experiment some time ago, and I found the results quite striking.

This illustration from my book “Sabertooth” shows the striking difference between how a digitigrade Homotherium would look (top) compared to a plantigrade one (bottom).
homotherium-digitigrad-plantigrad-low-res

At any rate, other specialists such as R. Ballesio and L. Ginsburg made quite detailed analysis of the functional anatomy of the feet in sabertooths and convincingly argued that Homotherium, and in fact all members of the family Felidae, extinct or extant, were perfectly digitigrade, with the possible exception of the earliest species comprised in he genus Proailurus. My own research in collaboration with paleontologists like Angel Galobart, Alan Turner and Manuel Salesa, added further evidence to confirm the digitigrade stance of Homotherium.
But while there seems to be a growing consensus about the posture of Homotherium, some specialists still think that heavier, shorter-limbed sabertooths such as Smilodon or Xenosmilus would have been plantigrade, and one of their arguments is the sheer mass of these robust animals. Such views imply some degree of confusion between the normal standing or walking posture of an animal and its running abilities. It is an observed fact that many digitigrade carnivores, such as dogs, are fast, lightly built runners, while heavy, robust animals like bears are plantigrade. But this does not imply a real correspondence between build and posture, and one must rememeber that among extant cats the hyper-robust jaguar, for instance, is perfectly digitigrade, just like the agile cheetah is. Whatever the case, we still see skeletal reconstructions that show those extinct cats with a bear-like, plantigrade stance.

The details of the limb osteology of these animals fit better with a digitigrade posture, but finding the creatures’ fossilized footprints would go very far in proving their actual gait and posture. And finally, earlier this year, Argentinan scientists M. Magnussen and D. Boh reported the discovery of two sets of carnivore footprints in a Pleistocene site near the coastal city of Miramar that belong, with all likelihood, to Smilodon populator, the largest and heaviest species of the genus. The tracks are the right age, the right size and the right morphology to correspond to Smilodon, whose fossils miraculously happen to be present in the same locality. And there has never been a cat-like carnivore in South America that even approached the size of Smilodon, so the attribution of the footprints looks pretty safe.

This illustration shows a reconstruction of Smilodon populator shown to scale with one of the recently discovered footprints. The print corresponds to the right forefoot.smilo-populator-con-huella

What about the cat’s gait and posture? The footprints leave no doubt that the animal was digitigrade, just like the much smaller modern jaguar is. The footprints also confirm that the animal’s claws were retracted during the walk, although there is one interesting detail in one of the prints, that corresponds to a forepaw: a small mark on the inner side of the footprint would correspond to the position of the dewclaw, which doesn´t normally touch the ground in modern cats. But, given the remarkably short metapodials of Smilodon combined with the enormous size of its dew claw, it would make sense that it would touch the ground at least occasionally, as it seems to have done in this case. Also, the footprints’ enormous width corresponds well with the immense size of the paws of this predator, whose trail has been finally found, more than a century after its fossils were recognized by paleontologists as those of perhaps the most powerful cat ever to walk the Earth.

Lessons from feline violence

Out in the wild, the big cats spend most of their time just resting, and it is only on rare occasions that one gets a glimpse of their full potential for explosive action. And yet it is those brief moments that their whole structure is designed for. When I sit at my drawing table conceiving an action scene, as in the case of my illustration of two fighting Barbourofelis, I try to get all the details of the action right, and I use my memory and all the reference material available to represent the conflict taking place.

This reconstruction of two Barbourofelis fighting over a kill was an attempt to portray sudden action
escena-barbourofelis-1-low-res

But last summer in Botswana we had a totally unexpected opportunity to see what a big cat fight really looks like. I referred to that episode in a previous post, but there is so much more about those amazing moments. One amazing aspect which unfortunately you cannot show in a painting is sound: the animals are impressively loud, and you don’t just hear the sound, it really gets to your guts. Another important factor is speed (it all happened in less than 5 seconds) but that is also impossible to show in a static image, even if it can be implied. There is a lot of other elements that can indeed be represented through drawing and painting, and they take a good deal of study to comprehend. It is a good thing that we can bring back our pictures and videos in order to elaborate an experience that struck us like lightning and will stay with us while we live.

Here is a picture showing one particular moment of the lioness’ hair-rising charge on the male
lion-fight-1-low-res

And here is a sketch showing a detail of this same conflict
furious lioness 7

Watch this video showing a few of the many highlights of our trip:

Book Review: “The Big Cat Man” by Jonathan Scott

Jonathan Scott lives a life that most of us can only dream of, spending much of his time in one of the most amazing wildlife areas in the world, Kenya’s Maasai Mara. Naturalist, writer, artist, wildlife photographer and world-famous TV presenter, he has turned the dreams of his youth into a reality, and the story of his life, told in his autobiography “The Big Cat Man” (Bradt, 2016) makes for a truly absorbing read. I suppose many young wildlife enthusiasts will read it looking for an answer to the question “how did he achieve it?”, and certainly that, plus the thrill of following Scott’s adventures and encounters with wildlife are more than enough reasons to read it. Complete with a stunning collection of photographs and Scott’s beautiful line drawings, the book guarantees an engrossing experience.

But for those who have read his earlier books and followed his TV programs over the years, deeper expectations emerge. What perspective has Scott gained after witnessing the changes that have taken place in his beloved Africa since he arrived there? What kind of transformations has he himself undergone during a lifetime observing and learning from Nature at her rawest? Scott does address these matters, and the answers may not be simple but they are fulfilling. While the book is a true page-turner, there are major themes in it that you see better after finishing. One of them is how achieving one’s dreams not only implies a struggle against the obstacles of the world outside, but also a fight against the darker forces of our own minds -an insight you don´t often find in autobiographies. He also makes it clear how sharing his life with his beloved wife Angie helped him find and develop his true self. The general impression that transpires is that only deep commitment brings about fulfillment, something that Scott experienced early in his life, when he renounced the chance of an academic career in South Africa that conflicted with his abhorrence of the apartheid system. Then, as often happens in life, giving up something left an open door for something better to come.

“The Big Cat Man” is a story about Africa as much as it is about Scott’s life. As the narration progresses, you can feel how Africa lured this young British farm boy through the early documentaries he saw on TV, which built his romantic view of the adventure-filled savannahs. Then, during Scott’s first exploration of the continent, Africa showed him her teeth, but also enough of her charm to keep him firmly hooked. And with the years, he not only came to enjoy her gifts to the full, but he also became what Africa had needed of him all along: a champion, a tireless defender of her nature and a chronicler that told the amazing tales of the wild, and especially of the big cats, for millions of people to read and watch all around the world.

Like so many people, I first came to Kenya attracted largely by the stories Scott told in his books (“Kingdom of Lions”, “A Leopard’s Tale”) and films (especially “Big Cat Diary”), and I was not disappointed in the least, but also I have seen change over the years, and not always for the better. Scott is the best promoter of Kenya’s natural wonders, but he doesn’t turn a blind eye to the problems that beset them. In the last chapters of the book he addresses these problems and gives hints to their possible solutions, but always with a sober touch of realism. He has seen too much of what greed and corruption can do to wildlife to believe in easy ways out of Nature’s current predicaments, which are after all, our own.

The life of Jonathan Scott is largely about his experiences with Africa’s big cats, but there is only so much of them that can be told between two covers. So, for those who aren’t familiar with his previous books, “The Big Cat Man” is a good introduction which should be followed by reading such classics as “A Leopard’s Tale”. But there is one final consideration that comes to mind when talking about the autobiography of a person who remains active and in full shape: why write an autobiography at all? Why expose one’s intimacies to the world? Scott himself reflects about this in a delightful essay in his blog, which I recommend you to read:
( http://www.jonathanangelascott.com/main/wordpress/2016/08/other-peoples-lives-who-cares-why-write-an-autobiography/ ). Inspiring others comes up as one of the best motivations, and it is well summarized in a phrase that he quotes from Roderick High-Brown: “It is a rare book that changes a life, a poor one that adds nothing to it”. I am sure that time and the readers will put “The Big Cat Man” firmly in the first category.

the-big-cat-man-cover

A BURST OF FEMALE FURY

One second the lioness seems to be sound asleep as the male delicately approaches her. The next second she is an exploding whirlwind of teeth and claws, and the thunder of her roar drowns any other sound from the surroundings, or from us.
We witnessed this burst of female fury in Northern Botswana during the last edition of our “Drawing the Big Cats” safari, and certainly none of us would like to have been in the place of the scolded young male lion. No real harm was done, but the lioness made a very clear statement.
How to capture the raw feline power of that scene with a simple pencil sketch? I try with a view of the angry face as the lioness snarls at the rearing-up male.

In this early stage I try to capture the general proportions of the cat’s head and the shape of the mouth opening with a few simple lines. It is crucial to get these lines right because I will be spending quite a few minutes with the details of the teeth and palate, and it is sooo frustrating to find out that the mouth was too narrow or the mandible was twisted after you had already wrought the details!
furious lioness 1

After some more minutes I have given shape to the main structures of the head and mouth, although It seems I will need to go against my own sketching rules and use the eraser after all: the tip of the nose looks to be projecting a bit too far forward!
furious lioness 2

Some more minutes into the work, and now I am ellaborating on the grayscale. Evolution has provided cats with a fantastic “natural makeup” to boost their emotional expressivity, and their faces are a study in tone contrast. Black lipstick, gothic style, stands in striking contrast against the pale fur of the muzzle, and one needs to be careful in order to show the difference between the dark tones of the lips and the darkness of the oral cavity.
furious lioness 4

In this provisionally finished stage I have insisted with the dark grey tones of the shadowy background. I remember the charging lioness as a fast moving tawny shape against the dark shade of a thick bush, with the fearsome canines flashing out. To capture this impression I need to spend some more minutes adding pencil strokes until I get a sort of dark mass from which the facial features stand out.
furious lioness 7

I never tire of quoting pioneer paleoartist Charles Knight when he said that you cannot pretend to be able to reconstruct an extinct animal unless you can properly depict its living relatives. As I further my work on the collection of extinct cat illustrations for my upcoming book project, I find it so useful to sketch time and again the big cats we have encountered in the wild. It is an exercise that never fails to enrich my perception of the animals and to deepen my admiration for them. Drawing is most fun when it implies learning, and sketching the wild cats of Africa teaches me something new everyday!

ANCIENT AFRICA: SABERTOOTH KILL AFTERMATH

In a few days we will be heading for Botswana for one more edition of our “Drawing the Big Cats Safari”. Our main goal is to observe the felines, but that is only part of what we get: we actually get a ticket to ancient Africa. The big predators are one key piece in the giant puzzle of living ecosystems, and a place that still can sustain its large carnivores is a place where the laws of nature remain healthily at work, and for that reason I experience every safari as a kind of time-travel.
On each trip, as I board the safari vehicle for the first game-drive, I feel as if I enter a different dimension. Pristine landscapes, untouched vegetation and the diversity of wildlife bring my senses to a state of natural alertness -not in vain human kind evolved in the African savannah! One unforgettable first-day game drive took place in Samburu, Kenya, in 1999. We had spent most of the day driving from Nairobi, and we had only time for a short evening drive through the reserve on our way to the camp for the night. As we drove through the scenic riverine woods along the margins of the Ewaso Nyro river, we found another vehicle that had stopped on the margin of the dirt track: they were watching a female leopard that had just killed an impala ram. Althought the high branches of the palm trees were still golden with the last rays of the sun, the deep bush where the big cat stood with its prey was already in deep shadow. Everyone on board of the vehicles was silent, aware of facing a high natural drama. It was almost as if we didn´t have the right to spy on this decisive moment of life and death, as if both predator and prey were emitting a sort of primeval energy that gave us the goosebumps. We just couldn´t take our eyes from the golden spotted cat and the athletic shape and powerful horns of the fallen antelope. We remained there in awe for many minutes as the cat started to feed and its tiny cubs emerged from the bush, as did an adult-sized young from the previous year, but then we had to hurry for camp.

Here is a picture of the leopard with her impala kill from our 1999 trip to Samburu
leopard and impala samburu 1999

In later trips I have seen leopards with their prey on several occasions, and each time the prey was an impala. It seems the fates of these two species are tightly linked, but the fact is the impala is an older inhabitant of the African woods and savannahs than the leopard. In Kenya there were impalas (genus Aepyceros) rather similar to the modern ones as early as the late Miocene, some 6 million years ago, while the earliest fossils of leopard ancestors (genus Panthera) are known from fossil deposits of Pliocene age, some 5 million years ago, from the Himalayas. Some time afternwards, leopard-like cats entered Africa, where they are first recorded some 3.8 million years ago, but the ancestral impalas had not been free of predation in the meantime, because several species of sabertooth cats shared their African habitats since the Miocene.

The impala is so well adapted to the ecotone between grassland and woodland, that it has barely changed in 6 million years. Its acrobatic leaps are among the most sublime, if sometimes underrated, spectacles of Africa. We saw this impressive ram in Chobe, Botswana, in 2014
impala d

Becuase of my professional bias, during my African trips I can’t help imagining how would those same places look in the distant past, and what animals would occupy the ecological niches of the modern species. If we could travel back to the early Pleistocene, about 1,6 million years ago, we might come across a predation scene where an impala nearly identical to the modern ones would fall prey to a sabertooth cat of the genus Megantereon. About the same size as a leopard, Megantereon would behave similarly to the spotted pantherine in many ways: it would hunt its prey through careful stalking, approaching to within just a few meters before launching an explosive attack. If the kill took place in the grass, the cat would drag its prey as soon as possible to an area with good cover to hide it among the bushes. After all, big hyenas and lion-sized sabertooths (Homotherium) roamed the plains and were always eager to steal the smaller cat’s kills.
But the shape of Megantereon‘s teeth implied some behavioral differences: on one hand, the sabertooth cat would be less able to haul complete large carcasses up the trees, because of its relatively fragile canines. Lighter, partly consumed kills would be easier to handle, although the cat itself was a good climber and at least could always save its own life by climbing to the higher branches.
But the most important difference concerned the killing bite, which implied a lot more bloodshed than in the case of modern cats, and thus if we could see Megantereon within the few minutes after a kill, it would be a rather gory sight.

Here is a reconstruction of Megantereon whitei from the early Pleistocene of Africa, taking a breath as it drags its impala prey to the bush for quiet consumption. Part of my book project “Big Cats of Africa, Past and Present”
megantereon arrastrando impala

Today we still have impalas in Africa, but Megantereon is long gone, a proof of the vulnerability of extreme specialists like the sabertooths and the resilience of adaptable species like the impala -and the leopard. But that doesn’t mean I don´t miss the possibility of seeing such a magnificent beast as Megantereon was!

GIRAFFES AND SABERTOOTHS: AN UNEASY COEXISTENCE

For a medium sized sabertooth like Megantereon, remaining unseen was of the essence. With its strong, muscular physique it was not nearly a long-distance runner, so it needed to stalk within a few meters of its prey in order to catch it after a couple of spectacular leaps. But its prey, including medium sized antelopes, pigs or even horses, had a lofty ally: the giraffe.
Since the late Miocene, members of the modern giraffe lineage evolved their long necks and tall forequarters, and inevitably became the sentinels of the savannah. From the privileged viewpoint of their 5 meter height, they miss little of what goes on around them

Some 7 million years ago during the Turolian (late Miocene) the giraffid Bohlinia attica had already developed the large size and unique body porportions of modern giraffes. It inhabited the open woodlands of Europe, giving them a striking “African” touch.
bohlinia attica low res

Any good wildlife tracker in Africa takes advantage of the presence of giraffes in order to locate the big cats. As soon as a predator moves in the vicinity, giraffes stop their browsing or casual walking, and stand motionless pointing with their stare in the direction of the carnivore. That habit is as convenient for the less tall herbivores as it must be annoying for the predators.

Back in the Pliocene and Pleistocene of Africa, the giraffid Giraffa jumae was a contemporary of the sabertooth Megantereon whitei. While the cat tried to take advantage of every element of the landscape to conceal itself, it could hardly escape the stare of the giraffe, which surely ruined many an attempted stalk!
megantereon stalking

SABERTOOTH HYGIENE: SURVIVAL OF THE CLEANEST

All cats devote a large chunk of their time to fastidiously taking care of their hygiene and if anything, sabertooths had even more reason to do so.
Right after killing a large prey, as it should do at least once a week, a sabertooth of the genus Megantereon would look like a bloody mess -literally. Unlike modern cats, its killing bite relied mostly on causing massive blood loss to ensure a rapid death of its victim, and that implied a somewhat untidy spectacle. But if we could find the sabertooth at any random moment, chances are we would find a pretty clean animal, which is only what you would expect from a cat.

If we could time-travel and come across the sabertooth Megantereon, it is very likely that it would be grooming itself
!
megantereon self cleaning

A sabertooth smeared in old blood would be pestered by flies, it would be prone to skin conditions, and would be more easily smelled by potential prey, so it needed to be quite conscientious about its grooming.
But of course there are other benefits to grooming, incluiding the fact, obvious to any cat owner, that it feels good and decreases stress! Social species would benefit from mutual grooming but a solitary animal, as Megantereon most likely was, would need to twist a bit around. But then its long and flexible neck would be a welcome aid in reaching those difficult spots!

MORE PALEO-MURALS THAT COULD HAVE BEEN

The most usual time for me to find long-lost sketches is when I am looking for something else. A few days ago while searching my old folders I came across a few drawings which I thought were lost for good. These included some discarded sketches for the murals of the 1993 exhibit “Madrid antes del Hombre” (in an earler post I shared a few sketches which I did for that exhibit).
The scene which probably changed the most during conceptual sketching was the reconstruction of the Miocene fossil site of Paracuellos. Looking at the site’s faunal list I first envisioned a forest scene where a pack of bear-dogs harassed a chalicothere mother and her young. I just chose from the list the species which looked most appealing to me.

Here is my first sketch for the Paracuellos site reconstruction. The bear-dog-chalicothere interaction is the undisputed centre of attention.
boceto paracuellos version 1 a

But the scientific advisors tought that the woods actually occupied only a small fraction of the area where the fossils accumulated, so they advised me to show a more open environment. Also they asked me to show other species which were more abundant as fossils at the site, because the bear-dogs and especially the chalicotheres were quite rare finds.

My second version kept the “stars” of the first sketch (the bear-dogs), but they were now cornered in the right-hand section of the scene, leaving room for the more abundant species. Also in this case the victims of the bear-dog attack were not chalicotheres but primitive rhinos.
boceto paracuellos version 2

Unfortunately the scientists found that even this second version did not show clearly enough the inferred environment around the site. Alluvial fans were an important feature of the arid, seasonal landscape, but it was too difficult to properly show them from a ground level perspective. So in the end an aerial view was favoured, and both the chalicotheres and the bear-dogs were totally left out of the scene!

Here is the sketch of the final version, with the reference lines I drew in order to transfer the drawing to the large canvas.
boceto paracuellos vers 3 baja

And here is the finished painting, alluvial fans and all, but no chalicotheres!
Paracuellos-baja

I won´t deny that all these changes implied some degree of frustration for me. I missed the opportunity to turn that chalicothere scene into a full-fledged, large format oil painting. Over the decades I made attempts to include that scene in other projects, but it simply never happened. Who knows, some ideas may be destined to remain forever at the sketch stage!

THE DOG WITH A CAT’S NECK

Modern dogs differ from other carnivores in one interesting anatomical feature: they have a “nuchal ligament”, a string-like structure that runs along the dorsal part of their necks and allows them to support the weight of the head with little muscular effort. Dogs share this feature with ungulates, but there are differences in detail: while in ungulates the ligament extends from the spines of the thoracic vertebrae to the back of the head (hence the name “nuchal”, meaning “attaching to the nape”), in dogs it only runs as far ahead as the second cervical vertebra (the axis), so the term nuchal ligament is somehing of a misnomer here. But, at any rate, what would a carnivore want a nuchal ligament for? Such an adaptation makes sense in a cow or a sheep, who spend many hours grazing with their heads down, an activity that calls for some passive mechanism to save the muscular effort of supporting and then lifting the weight of the head. But carnivores don’t graze, do they?
Well, what dogs do is track scent trails. They walk and trot for long distances, nose close to the ground, as they search and follow their prey’s smelly paths. And they also happen to be relatively long-legged carnivores, which implies they need a long neck for their snout to reach the ground as the animal trots. So the neck of a wolf, jackal or coyote is proportionally very long, but some of the muscles that turn it to the sides and pull it up are relatively reduced, compared to other carnivores, partly because their role is taken by the nuchal ligament.

Here is a drawing of the neck of a wolf (Canis lupus), showing the skull and vertebrae (top) selected deep muscles (middle) and more superficial muscles. See how the “nuchal ligament” actually doesn´t reach the nape, just the back of the axis vertebra.
dogs Wolf-neck low

But, have the necks of dogs always been like that? Several years ago, while working on the reconstructions of fossil dogs for our book “Dogs: their fossil relatives and evolutionary history”, Xioaming Wang, the late Dick Tedford and myself looked in detail at the anatomy of the fossil dog Aelurodon, from the American Miocene. Fortunately there is an amazing collection of fossils of these animals at the American Museum of Natural History in NYC, so we had all the information we could hope for. While studying the cervical vertebrae I found something strange about them: they somehow resembled the vertebrae of a big cat, such as a leopard, more than they did the same elements in a wolf. Concretely, the vertebrae were relatively short, and the processes for muscle attachment were proportionally larger, projecting farther away from the vertebral body. When I assembled the bones to create a reconstruction, the neck looked suprisingly short, and when I reconstructed the musculature of the neck on the basis of the shape and position of attachment areas, it was evident that this animal had a more powerful neck than a wolf of comparable size. There is no obvious evidence for the presence or absence of a nuchal ligament, but the morphology of the back of the axis, where the ligament would attach, is rather different from that of modern dogs. Also, the short neck and its powerful muscles would make the function of such a ligament rather irrelevant.

Here is a reconstruction of the head and neck of Aelurodon. The morphology of the cervical vertebrae (top) implies a relatively short neck, while the shape of muscle attachment areas speaks of very strong musculature (center). Both features resemble the necks of modern big cats. When external layers are added, we see that the animal’s head and neck woudl look powerful and socky (bottom)
dogs Aelurodon-neck low

These anatomical differences must have implied differences in behavior, but it is not clear what differences those would be. Given the simmilarities with a cat’s neck, it is tempting to assume a more cat-like hunting style for Aelurodon, implying that the predator was more able to handle its prey individually, using its paws to restrict its struggles, and using its neck as a base for delivering a more precise killing bite, a bit like big cats do. Also it is possible that trotting for miles in search of scent trails as some modern dogs do was a less important part of its behavioral repertoire. But it is also possible that the predatory behaviour of Aelurodon was essentially similar to that of modern wolves and it simply had not evolved some of their anatomical refinements.

A broad comparison of neck morphology in fossil dogs revealed to us that the first taxon to clearly show a modern wolf-like neck anatomy was the late Miocene and Pliocene genus Eucyon. This animal also developed proportionally longer forelimbs than any of its earlier relatives, probably reflecting an adaptation to drier, more open environments, and wider foraging areas. So it would make sense to think that a modern foraging stlye in these members of the dog subfamily caninae was accompanied by the development of a modern forelimb and neck anatomy.
Only additional research will take us closer to solve these riddles, but one thing is certain: just like in the cat family, fossil dogs reveal a diversity of adaptations that we could hardly suspect by looking only at the living species. And the dramatic difference that we see today between dogs and cats could have been a bit more blurred in the distant past!

To learn much more about dog evoution and fossil record, check our book:
http://www.amazon.com/Dogs-Fossil-Relatives-Evolutionary-History/dp/0231135297/ref=sr_1_1?s=books&ie=UTF8&qid=1461935130&sr=1-1&keywords=dogs+their+fossil+relatives+and+evolutionary+history

AMPHICYON: THE MIOCENE’S ALL-TERRAIN PREDATOR

In 1960, at a time when little was known about the anatomy and body proportions of bear-dogs, American paleontologist Stanley Olsen described a wonderful collection of postcraneal fossils of Amphicyon longiramus, from the Miocene site of Thomas Farm in Florida. Olsen’s paper profiled a kind of predator with no living counterpart. With a body size comparable to that of a modern brown bear, Amphicyon had a longer and more flexible back and a long, heavy tail. Its dentition resembled that of a dog more than that of a bear, and was better suited for consuming meat and bone, while still allowing the animal a varied diet.

Here is my reconstruction of Amphicyon longiramus, based mostly on Olsen’s descriptions of the Thomas Farm material
a-longiramus-recons-2 low res

In the middle Miocene, when sabertooth cats hadn’t yet attained their full size and dominance, amphicyonine bear-dogs like Amphicyon were the undisputed ruling predators, both in Eurasia and in North America. Although they could not run especially fast or long, they were capable of ambushing large animals using a vaguely cat-like hunting style, and then they could use their great muscular strength and powerful canine teeth to bring down and kill their prey. But with the late Miocene the rule of the bear-dogs was challenged by the appearance of such powerful felid sabertooths as Machairodus. Later relatives of Amphicyon, such as Magericyon, (best known thanks to the fossil sample from Batallones in Spain)adapted to the new times by becoming somewhat smaller and developing more specialized dentitions for killing and consuming large prey efficiently. But there was no resisting the empire of the machairodonts, and near the end of the Miocene the bear-dogs disappeared for good after many million years of successful evolution.

Here is the reference of Olsen’s papers:
Olsen, Stanley J. 1960. The fossil carnivore Amphicyon longiramus from the Thomas Farm Miocene. Part II, Part II. Cambridge, Mass: Harvard University, Museum of Comparative Zoology.