What Is, and what Causes Pyramiding?

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Jan 17, 2012
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I remember as a young boy one of the things that fueled my interest with chelonians was seeing how much was just NOT KNOWN about them. When I became fascinated with an animal, I ran to the encyclopedia to find out about it. I also always went to the library and checked out every book I could find on the subject. What is the best diet? Temperature? How about incubating eggs when I got them? Nowhere could I find anything about what temperature was best. So, I had to figure things out myself. Today we are so lucky with information at our fingertips. The internet – this forum! Yet still today, when it comes to chelonians, so much still seems to not be KNOWN. Most everything is, at best, debated. Some proposing one way, while another ‘expert’ says that won’t work. But we do have a chance now to see literally thousands of examples of results. But even results can be misleading if we don’t take into consideration the unique conditions that keeper in that part of the world provided. So little seems to be KNOWN!

Pyramiding is one of the best examples. In today's world of modern technology and scientific knowledge, there is still no proposed theory anywhere on how, metabolically, pyramiding even happens. It was just the last decade that it even became more apparent how to even prevent it. But that is still hotly debated. Most import of wild caught tortoises has been stopped for some time now. Pyramided tortoise has become the norm. Most pictures and artwork depicting tortoise show pyramided tortoise as “normal”!

We have enough evidence now to see that humidity is the key to preventing it. I can now grow smooth tortoises at will, after over 40 years of never being able to. I tried side by side groups of low protein vs higher protein groups. Groups of Fast growth vs slow growth. 3 groups of Store bough greens vs commercial pellets, vs natural grazing only. Stable temperatures vs night drops. Everything all the ‘experts’ said, I tried. Then I heard about humidity. I found this forum and read Tom’s thread on ending pyramiding. It all made sense immediately. I think it was the frustration of failing so many times and having to try so many proposed solutions that allowed me to find all the things that did not affect pyramiding. So many who have not had to struggle with it because of their location do not have that perspective. They will say it is diet, exercise, slower growth, etc, etc. All necessary for the most healthy of tortoises, but I found had nothing to do with pyramiding.

So, once I found out how to keep tortoises from pyramiding, the question still remained – why? Why did humidity work? Why didn’t diet or fast growth or exercise matter? I needed to know why! And no one, nowhere, knew why. There were enough pieces to the puzzle that were known. I had watched tortoise grow for decades. I monitored how pyramiding started and progressed. I could see what was happening. But to put the remaining pieces together took me into research in the anatomy and physiology of tortoise, keratin growth, bone growth, and even orthodontics.

A tortoise is a very uniquely modified animal. It is a vertebrate, yet carries its main skeletal structure on the outside. To protect this outside, exposed bone, another protective layer of keratin has developed over the bone. This is a unique adaptation as two hard surfaces normally do not come immediately in contact with each other in vertebrates. Bones are surrounded by cartilage and muscle - and even in more exposed areas, layers of hair and skin that cushion and provide ample blood flow. Keratin is also an interesting substance. Forming hair, nails, feathers, horns, it normally grows where the new keratin being formed is protected by living tissue from drying too quickly. Cuticles, hair follicles, feather sheaths, scalp around the base of horns, etc, etc. The tortoise, however, grows keratin that is exposed immediately to the external environment as it starts to spread and grow. No protective covering on the outside growth areas.

If you watch a tortoise grow and pyramid, you soon see that pyramiding is driven by the scutes, not by bone. For maximum strength, the scutes of a tortoise never align with the seams of an underlying bone. They all overlap - creating a very strong structure. Yet when a tortoise pyramids, the pyramiding ALWAYS follows the pattern of the scute. Where individual bones lay has no effect on the pattern of pyramiding. The scute remains a uniform thickness. It does not thicken in the center. The bone also retains a fairly uniform thickness but deforms to match to shape of the pyramiding. Bone would not grow that way unless something was forcing it to deform. I also saw that pyramiding was the forming of valleys at the seams of scutes, not the raising of the centers. A perfectly smooth tortoise will have the higher, more domed look that matches the peaks of a pyramided tortoise, not the valleys.

From studies on keratin, we see that keratin is quite hydroscopic when new and forming. It is more pliable and absorbs water easily. As it matures, and “dries” it becomes much harder and stiffer and loses most of its hydroscopic properties and no longer absorbs water and swells. It becomes a much stiffer and stronger, protective substance. Tortoises add very little thickness to a scute as it grows. New keratin is formed at the seams of the spreading scutes as a tortoise grows. As the underlying bone grows, the seam spreads between the scutes. Keratin spreads outward to fill this seam and slowly adds thickness, swelling to match the “finished” thickness of the scute. Often, this new keratin will swell thicker than the older scute section and create a ridge in a faster growing “smooth” tortoise. This will dry and age over the next several months and smooth out to a flusher level, but leave a distinct ‘growth ring’. The thickness of the scute of a 30” sulcata is pretty much the same as a 15” sulcata. New keratin is not added to the underside of the central parts of scutes as a tortoise grows.

They have no protective layer over the new keratin growth, so the outside of the newly forming keratin is exposed to the environment. If while this new keratin is growing and spreading, it is exposed to conditions that allow it to dry too quickly, it will lose its ability to continue to swell and fill in thickness. The underside of the keratin, in direct contact to living tissue (the epithelial layer) still is pliable and swelling. This imbalance forces the new growth to swell downward as it cannot continue to fill in upward. This puts a small but constant pressure on that epithelial layer and puts it in compression as it is being pressed into the bone below. This is the beginning of pyramiding.

How does this slight pressure deform bone? As mentioned earlier, the tortoise shell is very uncommon in vertebrates in having bone next to a hard surface. There is a very thin layer of tissue that separated the bone from the scutes called the epithelial layer. This delivers blood supply and nutrients to the bone and new keratin growth and creates a barrier between the bone and the hard scute. Epithelial tissues are everywhere in a vertebrate. It covers the outside of your body (skin), lines organs, vessels, and cavities. But it also is defined by not covering a hard surface and in direct contact with bone. However, there is one place I found something most similar to this positioning of hard surfaces. Teeth and the jaw bone. There is a layer formed between the teeth and the jawbone that separates and somewhat cushions the jawbone from the teeth. It is called the periodontal ligament. It still retains pockets of epithelial cells throughout that effects some of its functions. AND, it was in studying examples of how bone can be deformed or reshaped, I again was lead to teeth.

When a slight but consistent pressure is applied to a tooth, it puts the periodontal ligament into compression on one side of the tooth in the direction of the pressure. That triggers the formation of an important type of cell in our bodies called osteoclasts. Osteoclasts are specialized cells that break down and dissolve bone. Bones are constantly restructuring and rebuilding. Another type cell, the osteoblast – builds new bone. This adds density to our bones and grows our bones when we are younger. Under stress, (exercise) it is triggered to build density and more strength. Osteoclasts, on the other hand, are called into play to remove older bone, and also to tap into the stores of calcium and phosphorus in our bones in times where our levels of calcium or phosphorus in our blood drops too low. Our bones are more than an inert structural item. They are living, constantly remodeling stores of tissue and minerals.

So how do they move teeth? Apply a slight but constant pressure on a tooth. That puts the periodontal ligament in compression on one side of the tooth. That triggers the formation of a bunch of extra osteoclasts that form at that site of the pressure and start dissolving bone to relieve that pressure. On the other side of the tooth, the periodontal ligament is then in tension. This triggers osteoblasts that are called into action and an abundance of osteoblasts go to work forming new bone to fill in the area that is putting the periodontal ligament in tension. So - the bone is not deformed. It is broken down and removed on one side and new bone is built on the other side.

In our tortoises, when the new keratin dries to quickly, it is putting that epithelial layer into compression as the new keratin growth can only swell and fill in downward. The epithelial layer call osteoclasts into action at the site to dissolve and remove bone and relieve the compression on that epithelial layer. This creates a groove in the bone directly under the new growth. Even in smooth, “normal growth” tortoises, you can often see grooves in the bone formed by the growth rings. However, if the dry conditions persist and the tortoise continues to grow in conditions that are too dry, the newly forming seam will also press down on the epithelial layer over the bone and deepen the groove forming into a valley. If this continues, the actual plane of the bone is changed to the pyramided shape. Bone does not grow from the seams, but instead grows from wide areas throughout the bone. So, the tipped areas themselves (particularly along the vertebrals with more bones than scutes) will be growing bone in a direction that will simply add to the pyramiding. That will make it much harder to alter the pyramiding in a tortoise once it has progressed substantially. Yet a young tortoise, with just the start of pyramiding, can develop quite smooth future growth easily at an earlier stage that hasn’t progressed too far.

So - for me this answered all the questions. All the pieces fit and all the scenarios I actually see, anywhere, all fit. There are two things needed to pyramid a tortoise. Active growth and dry conditions. It is only by putting the epithelial layer into compression that osteoclasts will be formed to dissolve bone under the area in compression.

Diet will not matter. Pressure triggers osteoclast genesis. With poor diet you can have a tortoise with pyramiding PLUS metabolic bone disease. If anything, the pyramiding is releasing a bit more calcium into the bloodstream to help bone growth elsewhere! If diet is so poor that growth is stopped, of course there would be no pyramiding because there is no growth of new keratin.

Excess protein will not trigger osteoclast genesis. And certainly not only in specific areas under scute seams. Excess protein will create excess purines and possible stone formation problems. Smooth or pyramided!

Exercise does trigger osteoblasts genesis and better bone growth and density. It does not trigger osteoclast genesis and again would have no effect on localizing that under scute seams.

Fast growth does not affect pyramiding. You can have fast growing smooth tortoises and fast growing pyramided tortoises. Just as you can have slow growing smooth tortoises or slow growing pyramided tortoises. If they grow, fast or slow, when conditions are too dry – they will pyramid.

UVB exposure will not change pyramiding. It will certainly affect calcium uptake and utilization as D3 is necessary for that. So it will affect bone growth, but will not trigger bone dissolving in such a specific, localized area as only under the scute seams. In extreme cases, it will lead to metabolic bone disease as osteoclasts are triggered throughout the greater storage rich bone areas as it looks to release calcium back in to the blood stream. But that is also more concentrated in the hip and pelvic bones and plastral bones. Not at all calling osteoclasts into play under scute seams. Totally separate metabolic events.

Tortoises have ended up in the wild in “left over” habitats. They have been outcompeted and predated upon in any of the more favorable habitats. Their survival is because the have found way to survive in habitats that are much more hostile. Water is the key ingredient to survival. They are masters at maintaining it and finding microclimates that are less harsh. Nature gives them food and growth along with the moisture. In drier times, the food disappears, and the tortoise aestivates or brumates and does not grow. Their first few years, most tortoises spend their lives buried in the ground, or in leaf litter, always protecting themselves not only from predation, but from desiccation. In my own studies, I have found that during the growing season, beneath a large tuft of grass, virtually 100% humidity is maintained even when just above it the humidity reads 15%! This is where tortoises have found to not only remain humid, but have a ready meal at hand without exposing themselves to predation and desiccation.

In so many areas, their ‘natural range’ has been altered by man. With the advent of irrigation and reservoirs, the expansion of agriculture into their native ranges has even changed the food availability to drier times of the year and we see pyramided “wild” tortoises. Or so many now kept in compounds and fed through drier times and kept from digging and burrowing naturally – it is hard to tell what a “natural” tortoise looks like. We would have to look back 1000 years or so in many areas to really see a true wild tortoise in totally unchanged habitat. Certainly, in captivity, we have changed the way they live and the way they look.

Perhaps we are now learning enough to finally learn the conditions in which these amazing animals will do best. I am seeing more and more examples of tortoises that I believe look the way they were designed to grow. Maybe that will soon become the norm. Hopefully, in the not too distant future, we will see smooth tortoises again represented in the pictures and artwork depicting their species.
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