Joan Procter, Arthur Loveridge and the Pancake Tortoise. 2. Joan Procter in London: Structure of the shell and the question of defensive ‘inflation’

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Not content with gross anatomical description, Joan Procter threw whatever modern technique she could find to discover as much as she could about the Pancake Tortoises, now known as Malacochersus tornieri, sent to London by Arthur Loveridge, the dead ones at the Museum and the live ones at the Zoo. She used X-rays and fluorescent screen x-ray equipment provided by the surgeon Sir John Bland-Sutton (1855-1936) of the Middlesex Hospital. He was a keen supporter and vice-president of the Zoological Society of London.  She collaborated with Richard Higgins Burne (1868-1953, elected FRS 1927) who was Physiological Curator at the Royal College of Surgeons on the structure of the jaw. Burne was also a key member of the Zoological Society in the 1920s and 30s.

Boulenger had commented on the first specimens sent by Loveridge to confirm the pliable nature of the carapace and plastron. Instead of solid bone underlying the epidermal shields as in other tortoises, Joan Procter found areas with no bone at all, especially, as suggested by Loveridge in the centre of the plastron. Deep sutures between the shields also indicated a marked degree of mobility.

Figures from Joan Procter's paper showing the bony
carapace with the large areas (hatched) lacking bone

The bony plastron showing the lack of bone in the
large central area

In all, Miss Procter was able to work on 23 dead specimens, preserved in spirit, as well as handling the two live ones at the Zoo. Another unusual feature, apart from the areas of the carapace and plastron without bone, the tortoise is the appearance of teeth on both jaws. These teeth which are not true teeth are part of the jawbones with an overlying continuous horny sheath.

By studying young specimens and comparing the development of the carapace and plastron in other tortoises she concluded that the adult Pancake Tortoise resembles to a great extent the young of other species in which the bone then continues to grow and fill the gaps. In other words, the fenestration seen in the adult is caused by arrested development of the bony shell rather than by breakdown of a complete bony structure.

Procter noted the great variability in the shells of the Pancake Tortoise—the subject of a recent paper describing the variation between individuals in more detail.

A question that Joan Procter addressed, whether the bone of the carapace is derived from the skeleton or from the skin I will not deal with further here but will return to in the future since the question has been the subject of research for getting on for two centuries and there is recent work suggesting that old views are wrong. However, before turning to a functional problem it is worth considering how Procter argued on the mechanism evolution of the shell of the Pancake Tortoise. It is difficult for those of us who first got to know the history of theories of evolution in the 1950s to appreciate just how common Lamarckian explanations were in the 1920s or of how powerful and combative some of the individuals like Ernest MacBride FRS, who rejected both natural selection and modern genetics until his dying day, were in the zoological circles of London. Joan Procter sat on the fence:

     It can be argued on the one hand that the flattened carapace is brought about by the habit of living beneath stones and squeezing into rock-crevices. This habit, induced by environment, would be bound to have a modifying effect; for, during youth, the development of a domed and solid carapace would be interfered with by the constant application of pressure, and in a sufficient number of generations the ability to form a normal carapace might be lost altogether. The fact that the Burrowing Tortoise, T. polyphemus, has a thin or fenestrated and somewhat flattened carapace supports this view. Could this be proved experimentally, it would furnish a convincing argument in favour of the heritance of acquired characters. 

     On the other hand, it can be equally well maintained that an inherited tendency to the arrest in development is orthogenetic, brought about either gradually or as a mutation, and that the furtive habit of hiding beneath stones was the natural result, since the tortoise no longer possessed adequate protection from enemies. 

     Possibly both principles come into play, the reduced armour and loss of ribs being orthogenetic, and the depression and relative condition of the vertebrae being subsequently induced by the rockdwelling habit.

Apart from the developmental origin of the bony shell, the subject that has stirred interest in the Pancake Tortoise has been the question of ‘inflation’.

The suggestion that Pancake Tortoises inflate to jam themselves more effectively into crevices between rocks came from Loveridge (see previous post of 22 November 2018):

The tortoise takes full advantage of this flexibility, as I soon found on trying to remove one from beneath a boulder. It inflated its lungs sufficiently to obtain additional purchase against the roof and floor of its retreat and, bracing its strongly clawed feet—some of the claws were over half an inch long—used them as struts so as to render its extraction extremely difficult.

Joan Procter described the animal’s characteristics thus:

In general appearance it looks as if it had been crushed in youth and had only survived by a miracle. When taken in the hand alive it has a boneless feeling which is uncanny; both carapace and plastron react to pressure on the abdominal region with a springy motion, and the animal is able to inflate itself to a slight degree.

The key question, does the Pancake Tortoise inflate itself and thereby jam itself into a space between rocks, was tackled by Leonard Ireland and Carl Gans (1923-2009), then of the University of Michigan; their paper was published in 1972. They noted that only Robert Mertens, in a paper published in wartime Germany, had questioned the occurrence of inflation: wedging yes; inflation no, he had concluded.

Carl Gans

The background to their work was that Gans had recently worked with George Hughes (1925-2011) in Bristol to sort out the method of respiration in the Spur-thighed Tortoise, Testudo graeca, itself then a matter of controversy. This tortoise and other chelonians were found to draw air into the lungs using muscles that acted in a manner akin to a diaphragm in mammals but acting within the confines of a fixed frame, the shell. There was no mechanism to force air into the lungs (as in frogs, for example). To Ireland and Gans it seemed unlikely that inflation of the body occurs during a threat. They monitored the pressure in the lungs of the Pancake Tortoise while trying to pull it backwards out of an artificial dark crevice 10 mm higher than the depth of the shell. The tortoises attempted to dig their claws of their forelimbs into the floor and rotated their forelimbs outwards. Those actions raised the front of the body and wedged it in place. The hind limbs were stretched out to the rear such that the claws tended to engage in any irregularities in the floor. The authors remarked that the wedging action was most effective; they gained the impression that the forelimbs would have to be broken before the tortoise could be pulled free of a rocky crevice in the wild. At no time during this pulling and wedging in response did pressure within the lungs rise consistently. There was no inflation. Wedging was purely mechanical and achieved by the positioning of the limbs.

Although inflation of the body cavity appeared to have been excluded as part of the mechanism by which the Pancake Tortoise wedges itself into rocky crevices or under boulders of the kopjes on which it lives, that knowledge never found itself into much of the popular literature or have reached what was then the more scientifically-isolated world of the museums. Books and papers still appeared without any reference to the work of Ireland and Gans. Some make it appear that the degree of inflation is enormous, with the impression created that the tortoise is the next best thing to a puffer fish.

However, was the wedging action of the limbs shown by Ireland and Gans the only way the Pancake Tortoise can fasten itself into crevices? Their test apparatus was arranged such that the ceiing was 10 mm greater than the height of the tortoise’s shell. Calculating the depth (i.e. the distance between the outsides of the plastron and carapace) from the photograph they show and the approximately median length of the carapace of the animals they studied, any ‘bulge’ from inflation would have to reach a 23% increase in the depth between plastron and carapace in order to reach the ceiling of the artificial crevice, a surely impossible ask.

The wedging action also leaves the limbs exposed. While offering protection in a relatively wide crevice, would it not be better to seek a narrower crevice in which the legs and head could be withdrawn. In those circumstances, movement outwards of, say, the soft area of the plastron by only a millimetre or so would really jam the tortoise in place. This is the mechanism proposed by Moll and Klemens in a paper published in 1996 but which I have not yet seen. They suggest that drawing the legs into the shell can ‘inflate’ the soft area of the plastron thus supporting the original observations of Loveridge in the field and of Boulenger and Procter in the museum and zoo. How would that work and can predictions be made that could be tested experimentally?

Respiration in tortoises is very different to the process in other land vertebrates. The lungs are attached to the carapace and are inflated and deflated by a diaphragm-like structure separating the lungs from the other internal organs. As the limbs are withdrawn into the confines of the shell there is additional inward pressure on the body cavity and, indeed, movements of the limbs are known to take part in the movement of gases into and out of the lungs. For sufficient pressure to be built up inside the body cavity to push upon the gap in the plastron the lungs would also need to be full or probably very nearly full of air. The flow of air outwards from the lungs in response to strong and sustained withdrawal of the legs and head would have to be stopped. The other alternative to stopping the outflow from the lungs would be for the lungs to be emptied completely by the build-up of pressure in the body cavity. Because tortoise lungs are so large and so capacious it seems unlikely that the decrease in volume of the body cavity would be sufficient for the lungs to be emptied and for the the covering of the plastron to be pushed outwards.

Proceeding on the assumption that the lungs are held full or close to full, the most likely scenario is that the glottis is closed and that the pressure of gases inside the lung increases, as assumed by Ireland and Gans. The other possibility, that the ‘diaphragm’ between the lungs and the rest of the body cavity is held tight such that fluid pressure changes are not transmitted to the lungs seems unlikely since that membranous diaphragm would appear to be much more compliant than the horny layer overlying the ‘hole’ in the plastron.

If this mechanism, the movement outwards of the leathery centre of the plastron brought about by  withdrawal of the legs and neck, does operate the corollary is that the tortoise ceases to breathe. And here we come to the known ability of tortoises to hold their breath for long periods. As anybody who has tried to anaesthetise a chelonian using a gaseous anaesthetic will affirm, the tortoise usually remains unanaesthetised by simply holding its breath for tens of minutes while keeping its legs and head drawn into its shell. I have seen such a tortoise after about 30 minutes suddenly thrust its head out and forcibly exhale, and I do mean forcibly. The sudden exhalation was as if pressure was first applied to the lung and then the glottis opened. The best analogy I can think of is the movement down the runway of an aeroplane first held in check by the brakes until the engines reaches full power.

Other factors would come into play. Terrestrial tortoises have large bladders. If full, less inward pressure would be needed on the body cavity from the active pulling inwards of the legs and head; if empty, more. The legs and head would have to virtually seal the gap between carapace and plastron, otherwise the soft skin would be expected to bulge outwards rather than leathery plastron.

This latter point brings me to suggest that an experimental test of the bulging plastron hypothesis is needed; in other words an extension of the approach of Ireland and Gans to see what happens in narrower crevices. I am not entirely convinced by the present arguments in favour. The reason I suggest more work is needed hinges on the properties of the horny material that covers the large hole in the bony plastron. The late bob Davies had a pair of Pancake Tortoises in the early 1990s. When I handled them, I found the horny covering of that hole to be thick and relatively inflexible. However, there was ‘give’. A slight push on the centre would move it inwards by a few millimetres—the ‘springy motion’ described by Procter when she handled the first living examples at the Zoo. The question of whether sufficient pressure can be exerted on the body cavity to make that horny material bulge outwards even by a few millimetres needs to be answered.

Joan Procter’s legacy, judged at the time to have been a tour de force, stills leaves intriguing questions about the Pancake Tortoise.


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Ireland L, Gans C. 1972. The adaptive significance of the flexible shell of the tortoise, Malacochersus tornieri. Animal Behaviour 20, 778-781.

Mautner A-K, Latimer AE, Fritz U, Scheyer TM, 2017. An updated description of the osteology of the Pancake Tortoise Malacochersus tornieri (Testudines: Testudinidae) with special focus on intraspecific variation. Journal of Morphology 278, 321-333.

Procter JB. 1922. A study of the remarkable tortoise, Testudo loveridgii Blgr., and the morphology of the chelonian carapace. Proceedings of the Zoological Society of London 1922, 483-526.

Joan Procter, Arthur Loveridge and the Pancake Tortoise. 1. Arthur Loveridge in Tanganyika

To complete what I have to say about Joan Procter, I want to turn to what was then—and still is—regarded as her most important scientific investigation.

Deemed too chronically ill to be a university student, Joan Procter came to the attention of George Albert Boulenger at the Natural History Museum because of her enquiries about reptiles. He invited her to join him as an unpaid assistant when she left school in 1916. At the Museum she soon established a reputation for her work and when Boulenger retired in 1920 she took charge of the reptiles and received ‘a small stipend’; she was then 23.

She worked and published on a wide range of species as well as producing drawings, paintings and models for display cases. Her best known scientific work was that on the Pancake Tortoise published in 1922. She was able to do this work because Arthur Loveridge was sending specimens to the Museum from Tanganyika. His account of how he got the tortoises and why they were so sensational was published in his book, Many Happy Days I’ve Squandered first published in 1944 in USA and 1949 in UK.

     From Tabora I went to Dodoma, in central Tanganyika, the chief town of arid and desiccated Ugogo. It is a region that has always had a fascination for me. You never know what you will encounter on the leopard-haunted kopjes which relieve the flat monotony of the thorn-bush plain on which the township lies. 

     It was while scrambling over a kopje one evening that I came upon a strange-looking tortoise. The reptile was lying dead at the foot of a precipitous rock, some forty feet in height, near the summit of the hill which rose at least five hundred feet above the plain. From the flattened and fragmentary remains I concluded that the tortoise had been crushed by a falling rock and was of a species unknown to me. As Salimu and I examined it together we discussed its appearance, and I urged him to be on the lookout for more since he was free all day whereas I had only two hours each evening in which to go hunting. When a few days later he returned triumphant with a living example, I was much elated, for I recognized it as similar to the dead one and rightly assumed that it was a Tornier’s tortoise (Testudo tornieri), then considered the rarest of East African species and about the only one which I had not found. During succeeding evenings we located two further batches of the reptiles in crevices or beneath rocks but despite redoubled efforts found no more during the three weeks in which I was stationed at Dodoma. 

     The reason for the flattened appearance of these tortoises was now apparent; they could squeeze beneath rocks or into fissures which afforded them greater protection from hyenas and other carnivores than a strong shell could. Not only is their shell reduced to the thinness of stout paper but it is full of holes or fenestrations. Of these the largest is a great diamond-shaped opening that occupies most of the central portion of the lower shell or plastron. In such areas the creature is protected only by its handsomely patterned black and yellow, “tortoise-shell” shields. So soft and thin are the fenestrated bony plates forming the shell that it is a simple matter to squeeze the tortoise between finger and thumb. 

     The tortoise takes full advantage of this flexibility, as I soon found on trying to remove one from beneath a boulder. It inflated its lungs sufficiently to obtain additional purchase against the roof and floor of its retreat and, bracing its strongly clawed feet—some of the claws were over half an inch long—used them as struts so as to render its extraction extremely difficult. This can be accomplished eventually by gently and persistently working the reptile to and fro when you happen to be able to get a grip. I spent an hour, Salimu helping me, in dislodging three of the tortoises from a fissure into which they had clambered. Their flattened shells have a further asset; they enable them to right themselves quickly when they fall upon their backs, as must happen fairly frequently to tortoises living on rocky kopjes. Several times I have come across an unfortunate leopard tortoise (Testudo pardalis babcocki) which had slipped as it climbed some rock and fallen back so that the deep and convex shell lodged between two boulders. The poor tortoise, being unable to turn over, had perished miserably. 

     The agility of these light and long-clawed pancake tortoises was revealed when I put them in an enclosure surrounded by wire netting; about six inches of the wire was buried in the ground, leaving a fence two and a half feet high. While this was adequate to restrain Bell’s box tortoises (Kinixys belliana belliana), my pancake friends scoffed at it; they clambered up the netting to the top, where they balanced precariously for a fateful moment before toppling over to one side or the other. Nothing daunted if it was the wrong side, they would try again with such persistence that several succeeded in escaping. It was the same when they were put in a deep box; again and again, despite frequent falls, they climbed up in the corners in an almost incredible fashion. To my surprise I found that these tortoises from Dodoma could swim, though opportunities to practise the art must be rare in so arid a region as Ugogo. Had they been water tortoises like the familiar leathery flapjacks (Amyda spp) of the southern lakes and rivers or the fossilized Archelon of the Upper Cretaceous of North America, one would have explained their shell reduction as an adaptation to an aquatic life where a measure of lightness might facilitate swimming. 

     Duly labelling each of my half dozen tortoises Testudo tornieri, I shipped them off to the British Museum, where they arrived some months before I did. When at last I walked into Dr. G. A. Boulenger’s office, almost his first question was an inquiry as to what treatment or preservative I had employed to soften my tortoises and render them flat for packing! When I explained that they were naturally soft and that I had brought a pair back alive as a present for the London Zoological Gardens, he was amazed, declaring that they were the most interesting reptiles that had reached him during a lifetime devoted to herpetology. “What is this name Testudo tornieri?” he asked as he turned one of the reptiles over and over and glanced at its label. I gave him the reference and then and there he compared my series with the figures and description of Tornier’s tortoise. Finding them different in several minor respects, he asked if he might describe them as a new species (Testudo loveridgii) before the Academy of Science in Paris, of which he was president that year. 

     The announcement received considerable attention and the late Lord Rothschild urged me to get him a pair upon my return to East Africa. There seemed little likelihood at that time of my ever being within many hundred miles of Dodoma, but a year later the opportunity occurred for me to send Salimu. I told him not to spend more than a month and, whether successful or not, promised him his wages in addition to a bonus equivalent to one shilling for each tortoise he could find. Of course I was to pay his fare to and fro. He bargained for his wife’s fare also, and I conceded that. From our previous experiences both of us thought that these tortoises were extremely rare, so I was not surprised to learn that when he presented my letter of introduction to the provincial commissioner at Dodoma, the latter guffawed on reading it and said to Salimu: “So you’ve come to look for tortoises. Well, you’ll not find any here, for I haven’t heard of or seen one in all the years I’ve been here.” 

     Ten days or so later Salimu was back at Kilosa with a broad smile and sixty tortoises. Naturally he was pleased at making nearly two months’ extra pay in so short a time. “However did you manage to find so many?” I inquired. It had taken him the best part of three days to find the first, he said; then he showed it to the local tribesmen, offering them a few cents for any they brought him. Obviously the assumed rarity of the species was due largely to its secretive ways, for who would think of looking for tortoises beneath rocks? Yet it is there that they spend most of their time, emerging to feed only in the early morning. 

     It was in January that Salimu made this journey and found eleven under a single flattish boulder, where it is not unreasonable to assume that they were æstivating, for January and February are the hottest months in central Tanganyika. Yet it was in late January and February that mating took place among my captives, and the single egg was laid in July or August; one of these eggs was buried beneath a rockery in the enclosure. The fact that only a single egg is laid, an observation corroborated at the Philadelphia Zoo by Messrs. Conant and Downs, is eloquent testimony to the success of the adaptations which have rendered life so secure for the pancake tortoise that it has no need to lay a large number as do so many members of the order Chelonia. The eggshell is very thin and brittle and unusually elongate, for though it is only an inch or so in width it is from if to i| inches in length. 

     The hardiness of the pancake tortoise is attested to by the fact that, though it was midwinter when I took the first pair to Europe and they had to live in unheated trains and houses for over a week, one of them survived in the London Zoo for eight and a half years. During much of the journey they subsisted on bread and jam, for I had nothing else to offer them. Salimu’s numerous captives throve on lettuce or tender cabbage leaves, and one that I surprised on a kopje at Tabora was busily engaged in nibbling grass. 

     The sequel to the capture of the big series, intensively studied first by the late Dr. Joan Procter and in part by Dr. Otto Wettstein, was the latter’s discovery that Tornier’s original specimen was abnormal but might be matched by individuals in my series. Thus all represent one highly variable species now known as Malacochersus tornieri, for its many peculiarities justified the creation of a new genus for its reception.

Arthur Loveridge (1891-1980) at the outbreak of the First World War had just been appointed at the age of 23 as Curator of a new museum in Nairobi, Kenya. He was born in Penarth, near Cardiff, in Wales. His father was an ‘Ironmonger and Ship Furnisher’ who had been born in England; he mother was born in Ireland. Keen on natural history he had always wanted to be a museum curator. He had done a year as a student at University College Cardiff before getting a job at the University Museum in Manchester. He moved to the National Museum of Wales when he seized on the opportunity of the job in East Africa.

Carl Gans (1923-2009), who new Loveridge and who appears again as an important player in Part 2 of this story, wrote a splendid obituary on Loveridge. In it, he wrote:

The spectacular difference between Loveridge and other enthusiastic boy-naturalists was his total commitment to the pursuit of natural history as a career. In 1914, at the age of 24, he applied for the curatorship of the Nairobi Museum, advising in the application that he had over 300 cases of natural history and anthropological specimens and over 250 jars of “spirit-preserved” reptiles. He noted proudly that he was prepared to handle techniques of mounting and preserving all of his captures, described his complex system of registration and collecting numbers, and referred to an 80-page catalog, with short descriptions of all specimens, all typed by himself. Even his handwriting was small and meticulously formed with little change between top and bottom of pages or successive sheets. Field notes and labels (as well as his many letters) alike were beautifully readable.

The reason he was in that part of German East Africa first called Tanganyika after it was ceded to British control and now part of Tanzania is that he joined the East African Mounted Rifles and fought the German troops there. He collected specimens throughout this period, sometimes even while under fire. Specimens were stored in jars and bottles ‘liberated’ (in the British Army’s sense of the word) from the enemy. The war ended and after a time back in Nairobi he became Assistant Game Warden of Tanganyika in 1921. However, his location soon shifted.

As well as the British Museum and London Zoo, Loveridge sent specimens to the Museum of Comparative Zoology at Harvard, as well as amassing his own private collection. In 1924, Thomas Barbour, of that museum and with a very large private income, bought Loveridge’s collection for Harvard with one stipulation—Loveridge should come too. That he did and for 33 years he was at first assistant to Barbour and then Curator. He is said to have written his popular books because the pay was meagre for a curator who was not also a Harvard professor.

Stories of Loveridge’s curatorial habits abound, of a drawer labelled ‘string too short to use’, of books and specimens having to be returned to their particular place each night and chairs left properly arranged. Alfred Sherwood Romer (1894-1973) at the Museum from 1934 and Director from 1946 labelled Loveridge the “Demon Curator”.

Loveridge made five expeditions to East Africa, each lasting for a year, between 1926 and 1949. When he retired in 1957 he and his wife moved to a spot about as remote as anywhere in the world, St Helena in the South Atlantic. He made other expeditions, had trips to London and carried on working, and corresponding—slowly via the St Helena mail ships. He died there in 1980, aged 88.

I found this press photograph of Arthur Loveridge with his wife,
Mary, taken on his retirement from Harvard

Part 2 to follow considers what Joan Procter did with Loveridge’s specimens and the question of ‘inflation’.

Anon. Loveridge, Arthur (1891-1980). 2014. In, Contributions to the History of Herpetology, Volume 1, revised and expanded. Edited by Kraig Adler, pp 111-112. (Contributions to Herpetology 30, Society for the Study of Amphibians and Reptiles).

Gans C. 1981. In Memoriam: Arthur Loveridge. Herpetologica 37, 117-121.

Loveridge A. 1949. Many Happy Days I’ve Squandered. London: Scientific Book Club.

Williams EE. 1982. Arthur Loveridge—A life in retrospect. Breviora No 471, 1-12.