Monthly Archives: July 2013

Homotherium, slayer of giants?

The spectacular fangs of sabertooth cats have been often seen as possible adaptations to pierce the hide of giant, thick-skinned prey such as proboscideans. But living elephants are such formidable creatures that it is difficult to accept that they would be the main targets of any mammalian predator. And yet there are pieces of evidence which clearly show that, at least in some instances, sabertooths did hunt proboscideans.

At Friesenhahn cave in Texas ( a fossil deposit of late Pleistocene age) the bones of several sabertooths of the genus Homotherium, including individuals of different ages, were found in association with those of many mammoths and mastodons. The place was in all likelihood used as a den by the cats, and the proboscidean bones show clear tooth marks, proof that the sabertooths were eating from them at the site. The proboscidean bones corresponded to animals between 2 and 4 years of age, a time when they are still of “manageable” size for the predators, but less closely vigilated by the mothers who need to concentrate in protecting their younger, more vulnerable calves.

But even at such young age, elephants make rather inconvenient prey. Even with the long and flattened canines of Homotherium, the diameter of the elephant neck is just too big and the skin too thick for an efficient killing bite to take place, so the dispatching of prey is by necessity long as it gets slowly weakened through blood loss from relatively superficial wounds. On the other hand, the sheer size and strenght of even a calf of this age makes it very difficult for a single cat to keep it pinned down to the ground. This disadvantage is made more serious by the fact that Homotherium, unlike other sabertooths, had long forelimbs with narrow wrists and small, not fully retractable claws (except for the enormous dewclaw).

 

The scene below shows a group of Homotherium and a young mammoth in the early Pleistocene of Southern Spain.

Homotherium-and-young-mammoth-2013

 

So, if we look at the overall anatomy of Homotherium we see that it was not an ideally built “elephant killing machine”. In terms of the ability to single-handedly wrestle down a large prey, even a lion is better equipped, but then the sharp canines of Homotherium were a real advantage to inflict nasty, debilitating wounds.

For me, there are 2 conclusions to be gained from this overview of the evidence:

First, that in order to bring down young proboscideans as the Friensenhahn cave sabertooths obviously did, hunting in a group would be a distinct advantage, and in fact it was probably a necessary condition.

Second, that since the overall body build of Homotherium was not that of a “giant slayer”, the odds are that the systematic elephant predation we see at Friesenhahn was either a local phenomenon, or a seasonal one, or both. Elsewhere and at different times of the year, there was probably a variety of prey for Homotherium to take, but my guess would be that it most often concentrated on ungulates of horse to bison size, and whenever it had to hunt individually, it would certainly go for lighter animals like horses or antelope.

So, giant slayer? potentially yes, but only under the right circumstances.

To learn more, look for the book “Sabertooth” in late october!

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Kingdom of Sabertooths, Kingdom of Lions –a reflection

As the “World Lion Day” approaches, I feel like indulging in a little philosophical reflection… please bear with me, I promise to be brief!

I take it for granted that followers of this blog share my passion for the big, wild carnivores. But I know that for some people this passion might at times seem strange. And yet our preference is a time-honored one: shamans around the world have chosen the big cats as their totem animals and as guides for exploring the world of the unknown, and the fact that one of the oldest known Paleolithic sculptures features a lion-headed man indicates that such an affinity is deeply rooted.

With the sabertooths being my own “totem beasts” since childhood, I have had plenty of opportunity to wonder, WHY this fascination? I suppose that the ultimate cause must remain a mystery. But my encounters with the modern big carnivores in the wild have given me some food for thought.

My first encounter with a wild apex predator took place well over a quarter of a century ago. I was alone, on foot and unarmed, but there was nothing to fear: it was “only” a wolf; a magnificent Iberian wolf, trotting effortlessly –almost gliding- in the early morning light, among the broom and heather of the remote mountains of Asturias, in Northern Spain. The animal was impressive enough, but looking back I find that the impression it made was inseparable from that of the place. Those mountains became magical for me, as any place that can still sustain its top predators must be.

The magic mountains of the wolf, Asturias, Northern Spain. I took this picture in 1997.

SomiedoLago2

Years later I travelled to the African wilderness in search of the big cats, and the same thing happened: the places where I encountered the big cats became magical, strikingly attractive places for me. The lion may be king of the beasts, but what is a king without a kingdom? Conversely, a landscape depleted of its wildlife may be pretty, but a place where the big predators still rule is far more than pretty:  it is a place where the laws of nature are fully at work.

Lions in Samburu National Park, Kenya, 2006.

samburu-2006-lion-pair-low-res

Similarly, the fascination I felt as a child admiring the illustrations of sabertooths by Rudolph Zallinger had much to do with the way the artist had immersed the beasts in their long lost world. Posing dramatically as it stabbed a mammoth trapped in the tar pits, the sabertooth Smilodon seemed the unquestionable ruler of its legendary kingdom.

Well, I think that our admiration for the big carnivores embodies one of our most basic contradictions. On one hand, we humans somehow feel that nature has to be respected if we want it to keep nurturing us, and the big predators are a sort of guardians and living signs of a balanced system. But as members of human society we also perceive that it is other people who provide or deny what we need, making the balances of Nature seem almost irrelevant. In traditional societies shamans were the intermediaries between “ordinary” people, too immersed in their daily affairs, and the mysterious world of non-human nature. Today, the role of the shamans is mostly lost, but it could not be more necessary. Somebody has to transmit the message of the rulers of the other kingdom -the wild kingdom. Lions, wolves, and from their long lost past, sabertooths, all send the same message to us: “We predators have long ruled the wild Earth while abiding the rules of nature. Under our rule, landscapes remain fertile. Under YOUR rule, nothing lasts long”.

A lost Eden: the environment and fauna in the Lake Turkana Area (Kenya) in the early Pleistocene, with the sabertooth Homotherium as the temporary “King of the Beasts” -the proboscideans permitting!

KoobiFora

What use is a mandible for a sabertooth?

The combination of old fossils and new technologies is taking us closer and closer to understanding the adaptations of extinct animals, and in particular of sabertooths. One recent piece of research by Stephen Wroe and colleagues takes the fossils of the marsupial sabertooth Thylacosmilus from the collections of the Chicago Field Museum, and uses 3D scanning and FEA analyses to compare it with the more “familiar” felid sabertooth cat Smilodon. The Field Museum Thylacosmilus sample was recovered by the 1926 Marshall Field Expedition to Argentina, and it served paleontologist Elmer Riggs to publish an excellent description of the species in 1934. Many decades later, it remains the best and most complete sample of the species, and it was rightly chosen for this “rocket-science” study (you can see the paper following this link: http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066888 ).

The results of this comparison reassuringly confirm something that more conventional studies of the marsupial sabertooth fossils already indicated: that this animal not only had converged with placental sabertooths from its isolation in Cenozoic South America, but it had in fact taken the adaptations for a sabertooth way of hunting several steps beyond what we see in the true sabertooth cats like Smilodon. Sabertoothed predators had a different kind of killing bite than modern cats, so that when jaws were open at full gape and jaw-closing muscles were too stretched to pull with force, it was the muscles of the neck that came into action, pulling the whole head down to help sink the fangs into the flesh of prey. As my illustration here shows, the neck vertebrae of Thylacosmilus were very large with huge processes for muscle insertion, making it quite adequate for such a function.

thylacosmilus-neck

The new study shows that the skull of Thylacosmilus was well designed to stand the stresses caused by that kind of motion –pulling down the head to sink the canines – and less well prepared to deal with the stresses that would be generated if the canines had to pierce the flesh using mostly the forces generated by the jaw musculature (as it does in modern cats).

The authors conclude from their comparisons that the action of neck muscles was even more important in Thylacosmilus than it was in Smilodon, something that seems pretty evident from the results. But they go one step further and argue that the lower canines did not play any major part in the killing bite in Thylacosmilus. If that were the case, the mandible would still have its role in biting off meat from carcasses and slicing it with the premolars and molars, but it would hardly contribute to the actual killing of prey… may that be true?

Well, most sabertoothed predators have something in common: the area where the two halves of the mandible join under the incisor teeth, technically called the symphysis, is more vertical than in other predatory mammals, and it tends to develop vertical ridges along its antero-lateral edges. In some sabertooths, including Thylacosmilus, this shape is exaggerated and a downward, scabbard-like projection is created. In others, like Smilodon, the projection is nearly absent, but the shape of the symphysis remains unmistakably “sabertoothy”. It is tempting to see the projection as a sort of “protection” for the sabers, but in fact it is more likely related with the kind of forces that the symphysis has to withstand during the killing bite. In “normal” cats, those forces have a large lateral component, but in sabertooths vertical forces were overwhelmingly dominant, and that has likey shaped the anterior part of their mandibles. Paleontologist Bill Akersten in his elegant 1985 hypothesis of the ”Canine Shear-Bite” gave the lower canines and incisors a role in the killing bite, a role that at least partly accounted for the unmistakable shape of the sabertooth symphysis. While there are some studies of the form and function of the mandible in sabertooths out there, more analyses are clearly necessary. But as long as a sabertooth mammal retains a vertical, reinforced symphysis (as is the case in both Smilodon and Thylacosmilus in spite of the obvious differences), we have good reason to think that the mandible had an important role to play in the killing bite.

If you are interested to read more about this, look for the book “Sabertooth” in late October!

Here are a couple of references:

Akersten, W. A. 1985. Canine function in Smilodon (Mammalia; Felidae; Machairodontinae). Contributions in Science 356: 1-22.

Riggs, E.C. 1934: A new marsupial saber-tooth from the Pliocene of Argentina and its relationships to other South American predacious marsupials. Transactions of the American Philosophical Society 24, 1–32.

Book Review: “The Unfeathered Bird”

The book I am going to review here is not about sabertooths, but it is very pertinent to the basic theme of this blog; the combination of research and artistry as tools to investigate the nature of animals, either living or extinct.

unfeathered bird cover3

Many years ago, in a review of Tolkien’s “The Fellowship of the Ring”, C.S. Lewis wrote: “This book is like lightning from a clear sky”. I think it is no exaggeration to say the same about Katrina van Grouw’s “The Unfeathered Bird”. This book makes the secrets of bird anatomy available to the general public like never before, with a rare combination of masterly draftsmanship and clear, unpretentious prose.

There is nothing out there that can remotely compare to this gorgeous volume. The “East African Mammals” series of books by Jonathan Kingdon are an egregious precedent but of course they do not deal with birds. And yet these two authors have something very important in common: they are not using the illustrated book format just as a vehicle to offer the general reader a more or less simplified version of standard knowledge. On the contrary, their books give shape to, and share with us, the authors’ first-hand discoveries in the natural world.

This “firsthand-ness” (sorry for the invented word) makes Von Grouw and Kingdon part of a selected group of artists-naturalists that have taken to heart the marriage of Art and Science that we so often hear about, but so rarely see. There is a thread leading from the Ice Age painters of Altamira and Chauvet, to Leonardo da Vinci, to Charles Knight and a few others, who have looked at Nature with an eye that is at the same time keen, unforgiving, humble and admiring. They have all been researchers in their own right, and their well-honed drawing tools are used for depicting their findings in a thoroughly faithful way.

That is what gives Leonardo’s sketches their undying appeal: they are inseparable from his study subjects, a point that is missed by the countless imitations that only seem to notice the superficial “style”. And that appeal is every bit as vigorously present in Von Grouw’s drawings. They are accurate chronicles of her journey of many years in search of the secrets of birds, of the unseen relationship between internal structure and external shape. And that is the reason why it is fully justified to say that “you will never see the birds the same way again” after reading and admiring this book.

cormornat

There is so much in this book that you will not find anywhere else. van Grouw knows her subject in depth and has written a thoroughly readable text that is sure to tell you things you didn’t know about birds’ anatomy and adaptations, whatever your previous level of knowledge. But of course the core of the volume is the stunning collection of drawings that show the birds as the unfeathered creatures that the book title promises, or as clean skeletons in life poses, or anything in between, plus many drawings that show close-ups of details of a skull or a feet that reveal some striking adaptation.

If you have any interest in birds, or in anatomy, or in Nature, or in Art as the most honest expression of human creativity, you cannot miss “The Unfeathered Bird”: it celebrates all these things with contagious joy, but you cannot help noticing that this triumph has not been lightly attained. It has obviously taken blood, sweat and tears, and we have to be grateful to the author for that. I certainly am.

hornbill

Go grab  your copy FAST, for instance follow this Amazon link: http://www.amazon.co.uk/Unfeathered-Bird-Katrina-van-Grouw/dp/0691151342/ref=sr_1_1?s=books&ie=UTF8&qid=1373105554&sr=1-1&keywords=the+unfeathered+bird+by+katrina+van+grouw