What is “pyramiding”? This is probably the most frequently asked question received by those that are “knowledgeable” on tortoise care. So, let’s try to clear this up by giving you a somewhat simplified answer based on the research I’ve been able to collect.
Pyramiding is the excessive upward growth of the scutes (the individual segments that make up the tortoise's carapace or shell) that results in each segment taking on a pyramid-like shape. Optimal shell growth should be smooth and domed. This condition is rarely, if ever, found in the wild and is not treatable or reversible.
This malady is a form of metabolic bone disease. Less severe cases usually aren’t a problem unless dietary deficiencies are also a factor. However, severe cases inhibit lung function causing weakness or paralysis of their limbs, arthritis, nail problems, shell deformity, and in some unfortunate cases, a slow death. The condition usually occurs in the first 2-4 years of life.
If the tortoise’s basic needs are not being met then the scutes begin growing vertically instead of horizontally resulting in the “pyramids”.
Pyramidal growth syndrome is an observable malformation of the carapace, and has long been established as an important indicator of the quality of husbandry (Wiesner et al., 2003).
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It is interesting to hear what new tortoise keepers have learned about pyramiding. The current most popular response is that pyramiding is in fact, caused by lack of humidity. Actually, this is only the most current belief among the public. Among the scientific community, however, you will be able to uncover loads of hypotheses, theories, and ideas about how pyramiding arises.
There is a rich history of studies focusing on pyramiding that all come to different conclusions. When we read one paper, per-say the one stating that the cause is related to humidity, it may seem we have found all our answers. However, when we step back and consider all scientific findings as a whole, we can see that we have a lot of ideas but no real concrete answers.
Causes of Pyramiding
Pyramiding is caused by any, or all, of the following conditions:
- Low humidity in the first years of life.
- Lack of, or insufficient sun/UV ray exposure: Glass blocks the critically needed UVB rays.
- Sedentary life: Not enough exercise, too small of an enclosure.
- Inadequate diet: Overfeeding, lack of fiber, grain-based diet, too much protein, low calcium/Vitamin D, inadequate ratio of calcium to phosphorus.
- Disease of the thyroid or parathyroid glands.
Lets take a look at the history of pyramidal research - what are some of the past and present findings?
During the 1980’s, the strongest belief was that pyramiding was due to a high protein diet (Steams, 1989; Highfield, 1990). Steams (1989) proposed that excess dietary protein can cause pyramiding.
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Highfield (1990) subsequently reported that hatchling sulcata tortoises raised on an alfalfa pellet substrate developed more pyramiding than those that were raised on newspaper, even though both groups were fed a low protein vegetable based diet. He speculated that ingestion of the substrate (which was the high protein alfalfa) may have contributed to the shell deformities.
Long-time keepers questioned this hypothesis because they were not observing a direct relationship between high protein diets and pyramiding. There seemed to be more factors involved.
For instance, a personal communication in 1993 with keepers at the Wildlife Survival Center, stated that their young radiated tortoises did not follow this relationship. Their radiated tortoises had always been kept indoors for their first 2 years of life, before going outdoors full-time. Their diet had always been 18% protein.
The keepers noticed that the pyramiding was mild to severe during the first two years, then would greatly improve, if not disappear, after going outdoors full-time, despite being fed the same high protein diet. They had suspected that the most important factors were exposure to natural sunlight and more exercise (Innis, 1994; Personal communication with J. Iaderosa, 1993).
Wiesner and Iben (2003) later conducted a study to examine the effect of dietary protein level and environmental humidity on the degree of pyramidal growth. Out of three groups, they found that dry environmental conditions (24.3-57.8% and 30.6-74.8% relative humidity) produced taller pyramids than humid conditions (45‐99% relative humidity). Variable dietary protein, however, resulted in only a minor, positive impact on pyramidal growth. (Wiesner and Iben, 2003).
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These findings have flourished into a wide-spread belief that pyramiding is, in fact, caused by lack of humidity. But I’m sure if you asked the folks back in 1990, they would tell you that pyramiding is, in fact, caused by a high protein diet.
Despite the explosion of newbie keepers believing that lack of humidity is the true cause, scientists still continue to research alternative causes. Why would they continue to research alternatives when this is apparently a closed case?
Other causes that have been studied, include lack of calcium (Liesegang et al., 2007) or the use of supplemental heat at night (Heinrich et al., 2016). These studies found pyramiding was correlated with something other than high protein diets or the lack of humidity.
Image from Heinrich et al. (2016), which found that supplemental heat at night caused pyramiding in leopard and sulcata tortoises even when humidity was kept consistent between the two groups (control group / no supplemental heat, left; treatment group / supplemental heat, right).
The conclusion is that, so far, no one really knows what “causes” pyramiding. The studies outlined so far are faulty for one reason - most were looking for a single environmental cause to pin-point. Pyramiding is a symptom of poor care, and poor care can be caused by any husbandry-related factor.
The most well-rounded and most believable hypothesis as to where pyramiding arises stems from the research done by Alibardi (2005), who studied the proliferation of the epidermis (beta-keratin cells) of chelonians, not necessarily in regards to pyramiding.
However, what he found was that the proliferation of the epidermis in scutes of the carapace and plastron in the tortoise (Testudo hermanni) corresponded with seasonal changes. During fall/winter (resting season), only few beta-keratin cells were produced. When growth is resumed in spring (growing season), however, cell proliferation is intense and centralized around hinge regions and tips of scutes.
Numerous beta-keratin cells are produced around the hinge regions, forming a new thick corneous layer around the hinge regions, which constitute the growing rings of scutes (see diagrams below). The genes involved in beta-keratin production are largely regulated by hormonal and seasonal changes.
In other words, the beta-keratin will be deposited periodically, whether or not a tortoise continues to grow. If they are healthy and quickly growing tortoises, as they should be in the wild, their body volume will increase, allowing the new beta-keratin cells to be deposited in new growth areas.
If we consider captive-raised tortoises, which are almost always going to experience less-than-ideal conditions compared to their wild counterparts, there may be a lag in growth. The less increase in body volume, the greater the chances that beta-keratin will be deposited under old-growth, causing some buildup of beta-keratin.
Less-than-ideal conditions that may hinder the growth of a tortoise’s body mass may include: high protein, lack of humidity, deficiencies or excess vitamins, minerals, UV light, exercise, water, overall food intake, inappropriate artificial heat (all factors that have been previously suggested to “cause” pyramiding).
Altered image extracted from Alibardi (2005), which shows a schematic representation of how pyramiding may build each growing season if the tortoise mass does not increase.
Altered image extracted from Alibardi (2005), which shows a schematic representation of the hinge region (spreading, actively growing region between scutes). This region will proliferate beta-keratin cells and push them outwards. If old growth remains in its place, it will be uplifted, thereby forming pyramids.
Preventing Pyramiding
Now the good news…Pyramiding is preventable!
I have come to believe through all my trial and error, all the things I read and study, all the experiments done - heat, no heat, night heat, no night heat, fast growth, slow growth, higher protein, more calcium, better UVB, on, and on, and on - all to me only fit one basic take on this. I can't imagine a variable that hasn't been tried, yet all do fit one conclusion. Pyramiding is seen when you have high metabolism triggered WITHOUT humidity.
If I think about the tortoise in its natural environment, they ENDURE periods of food scarcity, and hot, dry weather. They basically stop growing and estivate during these periods to survive - waiting for the time to thrive. When the monsoons come, they have ample food with the rains and humidity. They grow in those conditions. They don't grow in food-scarce, dry conditions. It's really logical - food is available when it is wetter allowing the food to grow.
So warm + humid = grow time. In dry times, the food dries up, and tortoises stop growing. It's when we create an artificial condition they would never see naturally in their home environments that we see pyramiding. We provide ample food and heat & UVB in DRY conditions. We get their metabolism going, yet without one key ingredient - proper hydration.
Sulcatas seem to follow this pattern the most strictly. It seems where they come from, when it dries up, there is no water available, nor food, so they go in a real slow or no growth mode in those dry times.
For me this continues to confirm that fast growth has nothing to do with pyramiding.
What would fit all scenarios is that the keratin as it fills in over new growth areas, will stiffen, and become resistant to filling in in a thicker layer above, yet add additional keratin below. That would cause downward growth with successive layer. As the bone growth beneath (especially in younger tortoises) is much more pliable, it would follow this growth pattern.
However when kept in a moist environment, the keratin retains it ability to swell and add volume to the new scute in a more even, top to bottom, profile. Everything would fit this... extremely slow growth would not pyramid and the keratin layer is barely filling in over new bone and this effect does not have a chance to happen.
However, whenever there is faster growth, the larger new bone area we all see as those white lines in many species, will require faster keratin growth as well to follow. If in a dry environment, this effect will then cause the keratin to push the bone downward as the top layer of keratin becomes stiffer much faster than the bottom of the keratin.
Through measurements over the years I had always believed pyramiding was not an UPWARD growth of the scute, but a downward growth of the seams. A pyramided tortoise most always measured just as tall to the top of the pyramid as a smooth tortoise is to the top of the smooth shell.
Basically, yes. Yet I personally have grown dozens of tortoises in very controlled stable temperature environments, and only when humidity was increased, and still using the exact temperatures as before, did I see a dramatic decrease in Pyramiding.
Smooth with inadequate D3, Smooth with no sunlight, smooth with fast growth, food with inadequate calcium and even metabolic bone disease - yet smooth! Yet we never see smooth without humidity somewhere in the equation.
It also speaks directly to the issue I have noticed, and Tom and others have mentioned but there was never a WHY... How come tortoises seem to be very resistant to pyramiding once they reach a certain size?
Pyramiding is seen when you have high metabolism triggered WITHOUT humidity. If I think about the tortoise in its natural environment, they ENDURE periods of food scarcity, and hot, dry weather. They basically stop growing and estivate during these periods to survive - waiting for the time to thrive. When the monsoons come, they have ample food with the rains and humidity. They grow in those conditions. They don't grow in food-scarce, dry conditions. It's really logical - food is available when it is wetter allowing the food to grow.
So warm + humid = grow time. In dry times, the food dries up, and tortoises stop growing. It's when we create an artificial condition they would never see naturally in their home environments that we see pyramiding. We provide ample food and heat & UVB in DRY conditions. We get their metabolism going, yet without one key ingredient - proper hydration.
Sulcatas seem to follow this pattern the most strictly. It seems where they come from, when it dries up, there is no water available, nor food, so they go in a real slow or no growth mode in those dry times.
I'm proposing that the growth of the scute above the bone is the primary cause of pyramiding.
The study Mark! referenced showed that Keratin acts and forms differently in a dry vs moist environment. When dried the fibers actually form differently and become more stiff and resistant to a swelling that occurs with keratin that has not been excessively dried.
I'm proposing that in dry environments, and very slow growth, the keratin as it forms at the edges of the scutes does so in a fairly uniform manner. But when moderate to fast growth occurs - the faster spread of keratin, exposed to dry conditions, will cause the top to stiffen, and not continue to swell as it continues to form, while the bottom of the new scute keratin continues to grow in a thicker way. This pressure is exerted on the bone below and causes the new scute seam to be lower than the previous seam.
Many always seen to refute the humidity, or say there is no scientific basis - based on the way metabolically bone grows. They're right -its not the bone affected - its the scute affecting the bone! Just a braces can straighten teeth in a jaw or a corrective helmet's gentle pressure can straighten the growth of an infants head.
Or they partially accept it and say it is complex and many factors come into play. Yet we see time and again examples of smooth growth with humidity no matter which of the other "contributing factors" are left out in the care of the tortoise.
Smooth with inadequate D3, Smooth with no sunlight, smooth with fast growth, food with inadequate calcium and even metabolic bone disease - yet smooth! Yet we never see smooth without humidity somewhere in the equation.
Humidity: All turtles and tortoises require high humidity during the first 3 years of their life. Hatchlings and yearlings should have access to a water dish about 1” deep and have daily soakings. Adult chelonians should always have access to clean water and a soaking dish 2’-3” deep.
