Monthly Archives: February 2013
Make no mistake, if we are going to try and reconstruct the sabertooths, the modern, living predators are a vital reference. A cat is an amazing living machine, and we need to know how it works in order to make any sense of the fossil bones of its extinct relatives.
So, in preparation for the task of creating my sabertooth reconstructions, I set out, all those years ago to learn all that I could about the functional anatomy of their modern relatives. And for me, the best way to fix any findings in my mind was to make lots of sketches. Here are a few, some of them rather gritty -and untidy! These exercises really helped me to see sabertooth skeletons with different eyes, and to perceive the dry bones as part of a complex machinery including muscle and tendon.
1.- Here is a study of some of the muscles involved in the climbing action of a leopard. I used color codes and simplified shapes to get a clearer picture of trajectory and action of each muscle, and to visualize the points of origin and insertion in the skeleton.
2.- A study of some of the muscles involved in the gallop in the cheetah. This is part of a nightmarishly complex series of drawings where I tried to visualize the muscles according to the stage of the gallop during which they were especially active, and then showing them by layers.
3.- Another couple of drawings in the same series –even more maddening than the previous ones.
4.- A study of the mechanism of claw retraction in a cat. This is another of those aspects of cat biomechanics that I really needed to draw in order to fix it in my mind. Once you see how this works you understand that we should not talk so much about “retractable” but about “protractable” claws. Retracted is the normal, relaxed position of the claws, and active contraction of several muscles is needed for the animal to deploy its weapons.
To a large extent, modern big cats are the obligate model for sabertooth action. So, another necessary exercise for me in preparation for my sabertooth reconstructions was to make lots of sketches of big cats in action. I have enjoyed my share of encounters with the big cats in the wild, but in such occasions, every second is precious and I don´t even think of taking my sketch pad and start drawing in the savannah. I rather take as many pictures and videos as possible for future reference. But even so, sketch I must, so how I do it? You can always sketch the cats as they have siesta, walk or eat at the zoo, but for serious action I find that the best reference are wildlife documentaries, so what I did back in the VH days (yes, when I did these sketches I did not have a CD player yet…) was to view the action sequences, then pause the video for a minute or so and make a really quick sketch. Play the video until I reach the next relevant frame, pause, and sketch again. And so on. I did dozens of such sketches and in the process got some nice ideas for action sequences involving the sabertooths…
OK, a few examples now:
First, a series of sketches of various frames of a lioness in full gallop…
Then, a closer look at some details of the musculature…
…a few frames of a galloping lioness from a different angle…
…a less violent moment…
…and some sketches of a stalking lioness, with my interpretation of what muscles are showing where.
More to come!
Ever since the times of Georges Cuvier, the reconstruction of fossil vertebrates is known as a process that proceeds “from the inside out”, as we first draw the skeleton and then add succesive layers of soft tissue until we finish with the skin and fur. But, as I prepared my reconstructions of sabertooths, I also did the opposite exercise: to draw extant animals “from the outisde in”. What is the point? Well, it is easy to get the wrong mental picture of how the bones of an animal fit inside its body. One may naively imagine that bones are broadly in the center of the mass of soft tissue, but the relationship between the skeleton and the outline of the living animal is more complex, with bone coming quite close to the surface in some particular places (which the classic anatomists knew as “bone points”), while it is hidden under deep layers of flesh in other parts. In order to get used to the correct arrangement of flesh over bone, I did dozens of drawings of modern cats with their skeletons inside. I simply traced the outlines of big cats from photographs (many of them taken at the Madrid zoo), and then using as reference the positions of the “bone points” as illustrated in anatomy manuals, I drew the bones inside the soft tissue “envelope”. After a while the exercise gets easier and more fun -it is relatively simple to pinpoint the ankle, knee or elbow of the animal and place there the corresponding parts of the skeleton (calcaneum, patella, olecranon…) and so on, and then putting the rest of the skeleton in place. And then some things kept surpising me, for instance how far the nasal opening of the skull is behind the external nose of the animal…
Some of these sketches were done almost 20 years ago! Ever since then, I have had the opportunity to make many dissections and CT Scans of big cats, which have allowed me to refine interpretations of bone-to-soft-tissue relationships, but to this day I find that “bone-point” sketching is an enormously useful exercise, and one that you can do with the simplest of tools!
Now some of those old sketches:
First, here is a tiger walking leisurely…
Below, a jaguar…
Below, a lioness head in side view. Here, the eyes an ears are essential for inferring the position of the apertures in the skull, while the lower canine is especially useful for drawing the elements of the jaw. I often outlined the masseter muscle in these drawings, to check how the mass of this powerful muscle is partly obscured by the long hairs growing right behind it in many cat species.
And here is a little collection of sketches of lioness heads in different views. Here I also practiced positioning the eyeballs within the eyesockets, and trying to figure out the difference in size between the actual eyeball and the part of the iris that is normally seen between the living animal’s eyelids.
In forthcoming posts we will see examples of the opposite procedure -drawing the sabertooths from the inside out. That is when we can apply what we have learned from these simple but useful exercises!
En sus comentarios a un “post” anterior, unos amigos llamaron mi atención hacia una ilustración de la anatomía del guepardo publicada en el número de noviembre de National Geographic. Yo no vi ese número de la revista cuando se publicó, pero ahora me he puesto al día. Estos amigos señalaron errores anatómicos en esa representación, incluyendo entre los más serios los siguientes: 1) El húmero está invertido; y 2) las vértebras lumbares están al revés. Yo he encontrado otros errores alarmantes, por ejemplo el animal tiene sólo 5 vértebras cervicales (en vez de 7), de las cuales las 3 últimas están al revés; las escápulas no tienen la morfología correcta, con lo cual o bien pertenecen a otra especie, o bien corresponden a un ejemplar gravemente patológico; falta la garra del pulgar, rasgo especialmente característico del guepardo y esencial para su método de caza, etc. Estos errores van precisamente en contra de las adaptaciones anatómicas que se resaltan en los textos de figura, y de hecho un animal cuyos huesos estuvieran articulados como los de la imagen en cuestión no podría caminar, y no digamos correr a toda velocidad. Inevitablemente uno se pregunta cómo pudieron “colarse” errores tan garrafales. He encontrado un relato por parte del personal de la NG sobre el proceso de creación de esa imagen, que resulta revelador, lo podéis ver aquí:
Esta es una historia interesante porque nos muestra el potencial y los peligros de las tecnologías de representación en 3D, si se pone demasiada fe en ellas.
En un derroche de medios, la NG encargó escanear TODOS los huesos del esqueleto de un guepardo, pero luego dejó en manos de una becaria el ensamblar todos los huesos escaneados para crear un esqueleto articulado digital. La becaria consiguió poner casi todos los huesos aproximadamente en su sitio, pero “aproximadamente en su sitio” no es suficiente para una imagen como ésta cuya principal justificación es precisamente la exactitud anatómica.
En el museo de historia Natuaral de París se exhibe un esqueleto de guepardo que casualmente está montado en una pose casi exactamente igual a la de la ilustración en cuestión, y que nos permite comprobar la verdadera posición anatómica de los huesos. Podéis verla en este enlace (en realidad se trata de una reseña del libro “Evolution” en el cual se publica una foto de dicho esqueleto)
El hecho de que los huesos fuesen escaneados, y no dibujados o modelados por un artista, pudo dar a los editores una sensación de confianza respecto a la exactitud de los resultados, la cual si acaso podría estar justificada en lo que se refiere a la morfología de cada hueso (asumiendo que todos los huesos de la caja correspondan al mismo animal, cosa que no siempre ocurre) pero desde luego que no respecto al conjunto. Tal exceso de confianza puede llevar a una relajación injustificada del proceso de revisión. No es correcto relajarse en la confianza de que la máquina ha hecho el trabajo por nosotros, y sigue siendo necesario que alguna persona con verdaderos conocimientos de anatomía de carnívoros compruebe la exactitud del resultado final. Está bien tener máquinas a nuestra disposición pero conviene recordar que siguen siendo simplemente eso: máquinas.
Para mí, como entusiasta de los felinos, el lado más doloroso de todo esto es la impresión de que en el proceso de creación de la imagen se haya prestado tan poca atención al animal real, cuando precisamente una ilustración como ésta tendría que contribuir a divulgar las maravillas de la anatomía y adaptaciones de los felinos. Se han destinado recursos importantes a este proyecto, pero lo que yo echo de menos es más pasión e interés por los felinos.
Termino con una imagen: una comparación entre el galope de un guepardo y el de una cebra en esta foto que hizo mi hijo en Kenia el año pasado. Lo que os puedo garantizar es que los huesos que mantienen desde dentro a este felino maravilloso no están ensamblados como en la imagen digital que hemos comentado ¡Eso seguro!
In their comments to a previous post, a couple of friends called my attention to an illustration of cheetah anatomy published in the November issue of NG magazine. I had missed that issue when it appeared, but have caught up now. These friends point to some anatomical errors in that representation, including among the most serious the following: 1) the lumbar vertebrae are in reverse (front side pointing backwards); and 2) the humerus (arm bone) is also reversed. I have found other equally alarming errors, for instance: the animal has 5 instead of 7 cervical (neck) vertebrae, with the last 3 reversed; and the shoulder blades have the wrong morphology, and they either belong to a different species or to a badly pathological individual. These mistakes go against the very anatomical adaptations that the figure captions are highlighting (an animal whose bones were assembled like this would not be able to walk, not to mention run at high speed!!), and one wonders how such errors could happen. I have read the account by NG staff of how the image was created, in an extensive blog post which you can check here:
Now this is an interesting story because it points to the huge potential of 3D imaging technologies but also to the dangers if one puts too much faith in them!
As you can gather from the NG blog post, they scanned all the bones of a cheetah skeleton, making clear their intentions to use all the necessary resources. Great!. Then they put an intern in charge of assembling the whole skeleton in 3D in the computer, and here is where the problems started. The intern got most bones roughly in their right place, but for an illustration like this one, where anatomical accuracy is the whole purpose of the thing, “most of them roughly in place” is clearly not enough.
A nice mount of a cheetah skeleton is exhibited in the Natural History museum in Paris, and it is almost exactly in the same pose as the NG illustration. This one has the bones in the proper anatomical positions, and it is a good model against which to check the accuracy of the digital image. You can check it in this link (actually a review of the beautiful book “Evolution”, where a photo of the mount was published):
The fact that the bones were scanned and not drawn or modelled by an artist probably gave the editors a sense of confidence about the accuracy of the result, and that is justified as long as the morphology of the individual bones is concerned (assuming that every bone that is in the box belongs to the same animal, which some times is not the case: curatorial errors also occur!). Such overconfidence in the results may lead to undue relaxation of the reviewing process. It is wrong to just sit back and relax, trusting that the machine has done everything right for us. We still need someone with a real knowledge of carnivore osteology checking, bone by bone, the anatomical position and accuracy of each element. It is all right to have clever machines working for us but we should remember that they are and will remain just that –machines!
For me as a cat enthusiast and a passionate student of felid adaptations for many years, the painful side of all this is that I get the impression that too little attention is paid to the real animal in the whole process of creating an image with a huge potential to disseminate the anatomy of this beautiful cat. An enviable amount of resources have been used, but I miss more real passion for the cats themselves!
Finally, a picture: a comparison between the gallop of a zebra and that of a cheetah, in a nice photo taken by my son Miguel last year in Kenya. You can be sure that the bones that support this amazing cheetah from inside were not assembled like those in the digital image commented above!!!