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Home , Chelonoidis niger, Cylindraspis, Floreana Island, Hesperotestudo, Sclerodactylon

Tropical Natural History 20(2): 134–143, August 2020 2020 by Chulalongkorn University

Origins of the Extinct, Subfossil Galápagos Giant ( niger) of the Post Office Tube (Inferior) of : Voluntary or Accidental Occupancy?

DON MOLL1*, LAUREN E. BROWN2 AND ALAN RESETAR3

1Department of Biology, Missouri State University, Springfield, Missouri 65987, USA 2School of Biological Sciences, Illinois State University, Campus Box 4120, Normal, Illinois 61790, USA 3Amphibians and , Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USA * Corresponding author. Don Moll ([email protected]) Received: 17 January 2020; Accepted: 5 April 2020

ABSTRACT.– The origins of the remains of giant tortoises that have accumulated in vast quantities on the floors of caves in some locations where giant tortoises once lived have received only scant attention to date. The subfossil Galápagos Giant Tortoises () of Floreana Island’s Post Office lava tube (inferior) are the main focus of this paper with supporting data obtained from other populations and locations. These remains have historically been explained, if at all, as the result of accidental falls (e.g., via pitfall traps). With the accumulation of greater knowledge of tortoise ecology and paleoecology the likelihood of voluntary cave entry and exit, sometimes by large numbers of giant tortoises (e.g., the Aldabra Atoll Giant Tortoises), also seems plausible. If followed by occasional blockages of exits by geological phenomena such as roof collapse the tortoises could be trapped within as well. An inquiry into the available evidence for the occurrence of both phenomena is the subject of this paper.

KEY WORDS: giant tortoises, lava tubes, subfossils, Floreana

tube of Floreana Island (= Charles or Santa INTRODUCTION Maria) in the Galápagos Archipelago.

Hundreds of their remains are scattered on The Giant Galápagos Tortoises (Chelo- the floor of this cave-like lava tube. noidis niger complex) of ’s Townsend (1928) and Steadman (1986) Galápagos Islands are among the largest of suggested the tortoises fell through the extant land tortoises. They are also long ceiling “pitfalls” and became trapped, famous for their role as ships’ fare in the age resulting in death from injuries sustained in of sail due to their ability to survive without their fall or eventual starvation. We herein sustenance for months in the ships’ holds. A challenge their explanation of the tortoises’ more detailed knowledge of their biology means of entry, and suggest an alternative has gradually accumulated in more recent explanation for some of the tortoises present times (e.g., Blake et al., 2012; Blake et al., in the lava tube. 2013; Blake et al., 2015; Caccone et al.,

2002; Caccone et al., 1999; Pritchard, 1996, 2007; Rick and Bowman, 1961). However, MATERIALS AND METHODS relatively little has been published concerning the extinct subfossil forms Literature Search including the specimens of Chelonoidis The methodology of Brown et al. (2008) niger obtained from the Post Office lava was employed to obtain a maximum number MOLL ET AL. — ORIGINS OF THE EXTINCT, SUBFOSSIL GALÁPAGOS GIANT TORTOISES 135 of relevant references concerning the subject 1980). They are formed by flowing lava and matter of this paper. Searches employing may be subterranean or formed by crusting- numerous combinations of search words and over of surface lava channels. They may the search engines Google, Google Scholar have complex branching and can have a (Advanced Scholar Search), and JSTOR more or less horizontal or downslope surface Advanced Search were used along with opening (i.e., window) through which the traditional library-based searches of paper liquid lava within may escape, leaving a sources at Illinois State University’s Milner hollow tube. It has also been observed that if Library, and in LEB’s and DM’s personal a surface window does form, the still- herpetological and paleontological libraries. flowing lava may rebuild it and not flow Scientific and common names follow out. At other times, overflow may occur those designated by the draining the tube (Greeley, 1971a; Jagger, Working Group (2017). 1921). Roof collapse may eventually block Collecting History and Location of the tube when it is void of lava. When this Specimens occurs near the original surface opening, a In 1928, Townsend (Director of the New secondary opening may split off creating a York Aquarium) visited Floreana, one of the steep, vertical, well-like hole. southern Galápagos Islands (Latitude: -1° Post Office lava tube was described in 17' 30.60" S; Longitude: -90° 26' 1.79" W), detail by Townsend (1928) and Steadman where he observed hundreds of subfossil (1986). There are two elongate branches fragments of tortoises in a lava tube cave (“inferior” and “superior”) that are now (Post Office lava tube [inferior]) on the separated from one another by a massive northwest side of the island, and collected roof collapse. The inferior branch contains 12 nearly complete shells of extinct Giant most of the tortoise remains. Its opening to Tortoises (Chelonoidis niger). The following the surface was also formed by a roof year, 1929, K. P. Schmidt (Field Museum of collapse. This opening is ca. 12 ft. (3.7 m) in Natural History) and S. N. Shurcliff also diameter and was half-concealed by bushes. explored this same lava tube and found three Ground level beneath the entrance is ca. 20 additional shells in “perfect condition” ft. (6.1 m) deep. One side of the opening has which had apparently been overlooked a steep slope (Townsend, 1928). previously (Shurcliff and Schmidt, 1930). The Field Museum tortoises with nearly RESULTS AND DISCUSSION complete shells include FMNH 13522 (now

MCZ Herpetology R-32098) and FMNH The Tortoise Turnstile Scenario 13523 (2 specimens). A number of carapaces Townsend (1928), echoed by Steadman and other subfossil material are held by the (1986), stated that the tortoises found in the American Museum of Natural History and Post Office lava tube (inferior) must have Harvard University’s Museum of Comparative entered by falling through the near-vertical Zoology (D. Dickey, pers. comm.; Poulakakis opening left by the collapsed roof section et al., 2008). described previously. This would presumably Description of Study Area have occurred after the major roof rock fall Lava tubes are cave-like structures blocked the liquid lava exit pathway that associated with effusive volcanic eruptions of low viscosity basalt (Carlquist, 136 TROPICAL NATURAL HISTORY 20(2), AUGUST 2020 previously allowed any tortoises to enter could have been the case for some extinct and leave the lava tube at will. species also. Townsend (1928) suggested that, “With Moll and Brown (2017) reviewed and a steep slope at one side the unluckly [sic] summarized examples of several extant tortoise that tumbled in did not necessarily tortoise species known to utilize different strike bottom with a fatal crash but rather forms of rock shelters, from large caves to rolled down an incline it could not ascend.” crevices. This depended on the size, and As the shells of most Giant Galápagos sometimes age of the species in question. Tortoises are thick, hard, and tough (except Protection from predators, heat and the Pinta Tortoises [Chelonoidis abingdonii]), humidity fluctuation, cold temperatures, and most individuals falling ~6 m into the lava use as hibernacula are common benefits for tube in this manner would be unlikely to be these species. Most interesting in the seriously injured, if at all. Without an context of this discussion was the discovery accessible exit these tortoises would be of two caves on Grande Terre, Aldabra doomed to eventually die of starvation or Atoll by D. Hansen and his research team other stresses in the lava tube. (The collapsed from the University of Zurich that are used roof section in the Post Office lava tube by many Giant Aldabra Tortoises [superior] descended at a shallower angle, ( gigantea) to escape the resulting in fewer tortoises being trapped potentially lethal afternoon heat on the atoll than in the inferior tube [Steadman, 1986]). (see photos and text in Bittel [2016], Warne When Townsend (1928) and even [2016], and photo by Dr. Dennis Hansen in Steadman (1986) conducted their research Moll and Brown [2017]). Dennis Hansen (in there was very limited ecological or paleo- Bittel, 2016) believed the use of these caves ecological information available concerning by tortoises was quite ancient based upon Giant Galápagos Tortoises, or, indeed, the extent of wear of the rock surfaces in tortoises in general. As more knowledge has and around the caves. The mid-day heat of accumulated it has become apparent that Aldabra Atoll is an existential threat to another explanation for some of the tortoises tortoise survival there and shade is present in the Post Office lava tube is necessary for coping with the hottest parts plausible: the tortoises could have of the day. As Bittel (2016) stated, “For voluntarily entered the lava tube, and were giant tortoises living in the tropics you subsequently trapped within by some either find a way to get out of the sun or you geological phenomenon such as a roof die.” Naturalists have observed small collapse or landslide. juvenile, and larger adult tortoises on Caves provide favorable environments Aldabra Atoll utilizing shade in rock for some species of extant tortoises. The crevices and under clumps of Tussock caves’ other fauna may benefit from their Grass, Sclerodactylon macrostachyum, or presence also. For example, the large other shade-producing clumps (Bittel, amount of dung produced by Aldabra 2016; Coe and Swingland, 1984; Pritchard, Tortoises in the caves they visit seems to 2007). The Grande Terre caves, however, feed resident crabs and insects (Baxter, R.; provide considerably more shade space in Blake, S. and Hansen, D. in [Bittel, J., addition to those previously known shaded 2016]). It is reasonable to assume that this areas (accommodating up to 85 tortoises in the larger cave [Bittel, 2016]). MOLL ET AL. — ORIGINS OF THE EXTINCT, SUBFOSSIL GALÁPAGOS GIANT TORTOISES 137

As the Galápagos, , and 1870 in Bour et al., 2014). Large deposits of Mascarene archipelagos are within the their fossil and (mainly) subfossil remains tropical latitudes, the resident giant tortoises litter the cave floors of all three main islands must have coped with periods (if not daily and some of their smaller satellites, exposure) of extreme heat. The use of caves including caves of limestone karst and would have been a natural, simple, volcanic (including lava tube) origin. The behavioral mechanism to cope with heat condition of the remains vary greatly due to stress where accessible caves are available. the environments of the caves, the age of the Other reasons for tortoise aggregations in remains, and the degree of disruption of the caves, related to possible social interactions cave floors by and/or human traffic. among tortoises, and not just benefits In , the generally more fragile provided by the cave itself are also possible, morphology of the thin carapaces and but have not yet been identified in tortoises lighter skeletal structure are quite different (e.g., group mating behavior, kleptothermy, from most other tortoises (Bour et al., 2014; etc., have been observed in other reptiles Hume, 2014). Moll and Brown (2017) found congregating in caves and cave-like C. vosmaeri and C. peltastes of structures [S. Blake, in Bittel, 2016]). particularly interesting in regard to their There are few other recent observations possible voluntary use of caves as shelters of extant giant tortoises in caves. Pritchard since their remains are often extremely well (2007) recorded one very large, seemingly preserved and articulated, with numerous “deranged” Galápagos Tortoise (presumably complete or nearly complete sets of remains Chelonoidis becki) encountered by a BBC on cave floors despite their aforementioned film crew in a lava tube on Volcan Wolf, fragility. Signs of damage which would Isabela Island (=Albemarle Island). It was probably result from falls are often not presumed to have fallen in from an opening present, suggesting the possibility of above, but was unable to ascend the steep voluntary entry into the caves. slope leading back to the surface. Despite the long history of association Giant extinct tortoises which may have between humans and Cylindraspis on the used caves for shelter (or were victimized Mascarenes, and the existence of numerous by them) are known from (two published and unpublished accounts of species of Aldabrachelys). One species, A. observations of their natural history (e.g., grandidieri, may have been associated with Cheke and Bour, 2014), we are aware of the caves of Andranoboka (north of only one historical observation related to Mahanjanga) according to Cheke and Bour voluntary cave use. Bellanger de Lespinay (2014). (1671) wrote (on La Réunion) “through an The (La Réunion, instinctual sense, two or three days before , and Rodrigues) were inhabited bad weather (referring to a cyclone), the by five species of giant tortoises of the birds, tortoises and other , withdraw Cylindraspis (one, two, and two into rocks or caves from which they do not species, respectively – Gerlach [2014]). All leave until the bad weather has passed” (in are now extinct, but one live female (species Bour et al., 2014). Perhaps this should not unknown) was captured in a cave on Round be too surprising since scores of naturalists Island (22.4 km off the north coast of and trained researchers who have observed Mauritius) sometime after 1844 (Barkly, the Giant Tortoises of Aldabra Atoll over a 138 TROPICAL NATURAL HISTORY 20(2), AUGUST 2020 period of many years failed to detect their alone is staggering, however, and begs impressive daily migrations to and from the further inquiry. caves of Grande Terre. Early observations by Gilbert White in Shell fragments of the Giant North Carr (1952) suggested that a pet tortoise was American Tortoise, sp., “… much too wise to walk into a well” and have been found in Crevice Cave and Tom was perceptive enough to retreat from the Moore Cave in Perry County, south-eastern rim of a precipice it had encountered. Missouri (Hawksley, 1986). The latter Yerkes (1904) conducted research that specimen was collected from the clay and suggested terrestrial hesitated to walk gravel of a stream in the cave. off platforms a foot (.305 m) in height and The remains of Meiolania mackayi, an became even more apprehensive at greater Australasian Horned Turtle, have been heights, while aquatic turtles showed little discovered in the Pindaï Caves of New concern about leaving the platform at Caledonia (Bauer and Sadlier, 2000). similar heights. Case (1969), Patterson Finally, a bone of the (1971) and Routtenberg and Glickman ( radiata) with a tool cut on it (1964) demonstrated experimentally that a was found in a cave on La Réunion. As this variety of terrestrial turtles and tortoises cave is beyond the range of this tortoise, and were able to perceive and avoid deep visual the cave had been disturbed previously by cliffs. This degree of visual acuity, depth cave explorers (Bour, 1981), its transport to perception and judgement should make the the site by humans is considered likely. likelihood of accidentally tumbling into a Before the Fall pitfall extremely unlikely, yet evidence in A related issue when considering the the caves suggests otherwise. origin of tortoise remains in caves is, why Golubović et al. (2013) conducted are there so many tortoises that have experimental studies of willingness to “step” presumably fallen in? An obvious, partial off a 50 cm high step by Hermann’s answer is that animals have steadily fallen in Tortoises ( hermanni) from a rocky, through the pitfalls described above by rugged, island habitat compared to those Townsend (1928), Steadman (1986) and from a lowland plain habitat in Macedonia. others in the Galápagos Islands, and in Bour They found that significantly more tortoises et al. (2014) and Hume (2014) in the from the rugged habitat were willing to take Mascarene Islands over the millennia that the plunge compared to those from the tortoises and caves have been present. plain. Golubović et al. (2013) believed that Additional contributions could have been the more rugged habitat required greater made through water transport of already boldness in its resident tortoises in to dead animals into the caves (Hume, 2014), accomplish essential tortoise requirements human transport for butchering, cooking, (compared to lowland plain tortoises) even etc. (Bour, 1981; Cheke and Bour, 2014), or though risks were involved. Indeed, they in the case of small tortoises, perhaps observed tortoises in the field losing their transfer as prey by cave-dwelling owls balance and falling from steep cliffs they (Steadman, 1986). The sheer quantity of the were attempting to ascend (non-fatally). remains which have been discovered in They also found dead tortoises at the foot of caves in the Galápagos and Mascarenes 15-30 m high cliffs atop which they previously observed living, active tortoises MOLL ET AL. — ORIGINS OF THE EXTINCT, SUBFOSSIL GALÁPAGOS GIANT TORTOISES 139 had been present. Griffiths (2014) also population extending from the southern recorded a fatal fall of an introduced lowlands into the uplands. The lowland Radiated Tortoise (A. radiata) a month after dwellers were the first to be decimated by its release on Round Island in the collectors because of the greater ease in Mascarenes. It had tumbled about 71 m acquiring them there. The upland tortoises down a rock slab and she considered such were able to survive a bit longer because the falls “… not uncommon for tortoises.” rugged uplands made collecting more Many tortoise populations live in rocky, difficult. The explanation for the demise of uneven environments and individuals must the last upland Pinta Tortoises may never be often travel extensively to meet their needs fully known. in spite of the possible dangers along the Although the ravines in question did not way (Calzolai and Chelazzi, 1991; lead into subterranean caverns, the Golubović et al., 2013; Longepierre et al., likelihood of similar behaviors which could 2001). Individuals from populations in lead to cave entrapment seem plausible. lowland plains and other less rugged Other factors could influence tortoise falls habitats may be at a disadvantage if also. Male tortoises are often more active confronted with the opposite as Golubović (Lagarde et al., 2002; Lagarde et al., 1999) et al. (2013) have demonstrated. Therefore, and more agile than females (Bonnet et al., it is interesting that Miguel Castro and 2001), although Golubović et al. (2013) David Cavagnaro (in Pritchard, 2007), noted observed no significant difference in high mortality in (now extinct) jumping ability between males and females Galápagos Giant Tortoises (mainly males) from the populations tested in their study. presumably resulting from falls into upland Male Galápagos Giant Tortoises are known ravines. They suggested that grazing to chase females (Pritchard, 2007) and these competition from introduced goats at lower higher male activity levels, and perhaps the altitudes had forced the tortoises to forage at distractions inherent in intersexual premating higher altitudes in more rugged habitats behavior (e.g., perhaps with females running where fatal falls into ravines would be more into pitfalls to escape males, pursuing males likely due to their lack of experience in entering the pitfalls, etc.) and intraspecific coping with such obstacles in their male combat, might increase their likelihood movements. Despite their possible reticence of stumbling into a pitfall trap. The in negotiating uneven, fractured terrain, the overwhelming male bias in mortality in the requirements for finding food, mates, etc., Pinta ravines examined by Pritchard (2007) may have forced displaced lowland forms to suggests greater male activity levels may be take risks they would have declined in more a factor, but the male-biased sex ratio normal times and habitats. Pritchard (2007) observed in this dwindling population discounted their hypothesis, but Golubović before its total demise (Pritchard, 2007) et al. (2013) might have predicted such masks the significance of this factor. Many results if lowland populations shifted into “surviving intact caves are well concealed higher altitudes, and more rugged habitats to with small, often precarious entrances” which they were poorly adapted (Hume, 2014). These may increase their behaviorally. Pritchard (2007) argued that likelihood of remaining undetected by the upland tortoises were just the last wandering tortoises, especially if partially remaining individuals of a once continuous concealed by bushes (e.g., Hume, 2014; 140 TROPICAL NATURAL HISTORY 20(2), AUGUST 2020

Steadman, 1986; Townsend, 1928). Individuals Even the presence of the intact or nearly could also potentially seek an interior cave intact remains of the La Réunion Island water supply, seek out potential mates caves are attributed to falls or water inside, or seek shelter from the conditions transport (Hume, 2014). Uncertainty will experienced outside the cave. John B. always be an issue when attempting to Iverson (pers. obs.) has observed Red- reconstruct the past, but it can never be Footed Tortoises (Chelonoidis carbonarius) completely avoided in paleoecological using “borrowed” armadillo burrows for research. Decisions must be based upon the shelter and Branch (2012) has recorded the best available evidence, and in this case the use of animal burrows as shelters by Cape data suggest that some of the remains in tortoises ( areolatus and H. these caves could have resulted from femoralis). A tortoise which misjudged the voluntary ingress and subsequent entrapment, depth of a “presumed” burrow and tumbled in addition to, or instead of, accidental falls. into a cave below could be interred permanently as a result. Giant Galápagos CONCLUSIONS tortoise remains have been observed in deep crevasses formed by collapsed lava tubes Water-, predator-, and human-mediated (Hennessy, 2019). It is also possible that transport, accidental falls, and voluntary some tortoises could have been trapped in entry and subsequent entrapment are lava tubes by simply walking across their possible mechanisms resulting in the roofs, causing them to collapse. Some parts accumulation of tortoise remains in caves. of their roofs are very thin and unstable Voluntary entry followed by entrapment because the rocks which form them are only appears to best explain the presence of some held together by pressure exerted against of the subfossil tortoise fauna of the Post each other. A could be heavy Office lava tube (inferior). In order to enough to initiate such a collapse (T. Banik, determine which is the most likely pers. com.). explanation for the majority of the remains Despite the accumulated direct evidence discovered in a particular location, the from living tortoises, and indirect evidence following suggestions are offered: 1) The suggested by the subfossil remains from condition and abundance of the shells caves discussed in the Mascarene Islands should be scrutinized. The presence of many (mainly), there are evidently researchers that intact or nearly intact carapaces, plastrons, have not considered voluntary cave ingress and delicate skeletal elements in a cave, and use as a mechanism to explain the especially those characterized by particularly presence of fossil, subfossil, and/or recent thin shells and less sturdy skeletal elements remains in caves such as the Post Office (e.g., the Mascarene Rodrigues Cylindraspis lava tube (inferior) of Floreana Island. It is [Hume, 2014] and the Pinta Island interesting that Bour et al. (2014) and Hume Galápagos Tortoises [Pritchard, 2007]) may (2014), in the chapters in Gerlach (2014) suggest voluntary entry. 2) The geological that mainly deal with Mascarene Islands and chronological history of the caves Tortoise cave remains, never mention the themselves should be considered in as much possibility of voluntary entry with the detail as possible to determine when and exception of the historical account by where travel in and out of the caves might Bellanger de Lespinay (1671) quoted earlier. MOLL ET AL. — ORIGINS OF THE EXTINCT, SUBFOSSIL GALÁPAGOS GIANT TORTOISES 141 have been feasible or not. The lava tube Few or no caves would be expected to caves like Floreana’s Post Office lava tubes provide all of the necessary criteria to would often have been likely to allow establish a completely certain explanation tortoise entry soon (geologically speaking) for the origins of its fossil or subfossil after their lava drained out through tortoise fauna. The more criteria evaluated, relatively horizontal or downslope openings as described above, that suggest the described and portrayed by Carlquist (1980) likelihood of one explanation over another and Greeley (1971a, b). Subsequent would be extremely valuable in contributing blockage by roof collapse and/or landslides to a consensus viewpoint concerning the would have obstructed such movement and cave faunas’ origins. This approach would entrapped tortoises within, while pitfall surely be better than automatically assuming openings in the ceiling would allow only that all the tortoises within result solely one-way entry from above in the future. from accidental entrapment by pitfall or Sophisticated dating techniques should be other involuntary means. Voluntary cave employed to pinpoint the timing of those use by extant tortoises is too prevalent and phenomena and to evaluate the resulting widespread to be excluded from consideration tortoise mortality patterns. For example, the in paleoecological research designed to presence of large numbers of subfossil elucidate use patterns of the past. tortoises of the same geological age within a cave might suggest voluntary entries, and ACKNOWLEDGEMENTS subsequent entrapment within (or perhaps a mass mortality event followed by We thank Tenley Banik, Evan Brown, interment). Accidental entry by falls and Jill Brown, Angelo Capparella, Janice Moll other types of misjudgment may be and Ben Sadd for critically reading the suggested by the presence of subfossil manuscript, and Janice Moll for typing the tortoises of various age periods, perhaps in manuscript. David Kizirian and David different strata on the cave floor. 3) Dickey of the American Museum of Natural Preferably, the cave floor remains should be History provided holdings details on undisturbed by animal and/or human Townsend’s tortoises from Floreana in the intrusion and excavation until investigations AMNH collection. of the above phenomena are initiated.

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