In the contemporary fauna the giant land tortoises are Tertiary relics. They survived at present only in several highly remote and restricted areas of the World. Their present distribution is pantropic and includes Africa, South America, Southern Asia, some islands of Oceania and the Indian Ocean. All species are herbivorous. By their enormous size giant land tortoises are the largest representatives of order Testudines Batsch, 1788 (Chelonians) of Class Sauropsida. The shell length of the largest recent species, the Galapagos tortoise (Chelonoidis nigra (Quoy, Gaimard, 1824)) is up to 1.80 m. Body mass of the largest individuals is over 300 kg, while their age is estimated at over 200 years. These measurements are much smaller than the size of the largest extinct species of the order (Testudo atlas (Falconer, Cautley, 1844), also known as Colossochelys atlas Falconer and Cautley, 1844. Its carapace length was up to 2.10 m, and height – up to 1.80 m. The total body length was about 2.70 m, and body mass – up to до 3000–4000 kg.
According to recent conceptions on the systematics of the giant land tortoises (until recently traditionally placed in the genus Geochelone Fitzinger, 1835), at present exist 18 recent species of 9 genera: Aldabra Giant Tortoise Aldabrachelys gigantea (Schweigger, 1812) – Aldabra Athol and the Seychelles; Radiated Tortoise Astrochelys radiata Gaimard, 1824)) is up to 1.80 m. Body mass of the largest individuals is over 300 kg, while their age is estimated at over 200 years. These measurements are much smaller than the size of the largest extinct species of the order (Testudo atlas (Falconer, Cautley, 1844), also known as Colossochelys atlas Falconer and Cautley, 1844. Its carapace length was up to 2.10 m, and height – up to 1.80 m. The total body length was about 2.70 m, and body mass – up to до 3000–4000 kg. (Shaw, 1802) – South Madagascar (introduced in Reunion and Mauritius); Angonoka or Angulated Tortoise Astrochelys yniphora (Vaillant, 1885) – Madagascar; Red-Footed Tortoise Chelonoidis carbonaria (Spix, 1824) – Central South America and the Caribbean; Chaco Tortoise Chelonoidis chilensis (Gray, 1870) – Chacco (Argentina and Paraguay); South American yellow-footed tortoise Chelonoidis denticulata (Linnaeus, 1766) – Central America, northern part of South America and the Caribbean; Galapagos Tortoise Chelonoidis nigra (Quoy, Gaimard, 1824) - Galapagos Islands (Ecuador); Indian Star Tortoise Geochelone elegans (Schoepff, 1794) – India and Ceylon; Burmese Star Tortoise Geochelone platynota (Blyth, 1863) – Burma (extinct in the wild); African Spurred Tortoise Geochelone sulcata (Miller, 1779) – Africa (south regions of Sahara); Elongated Tortoise Indotestudo elongata (Blyth, 1853) – Hindustan and Indochina; Forsten’s Tortoise Indotestudo forstenii (Schlegell, Müller, 1844) – Sulawesi and Halmahera (Indonesia); Travancore Tortoise Indotestudo travancorica (Boulenger, 1807) – Southwest Hindustan; Asian Forest Tortoise Manouria emys (Schlegell, Müller, 1844) – Hindustan, Indochina, Sumatra and Borneo; Impressed Tortoise Manouria impressa (Gьnther, 1882) – Indochina; Leopard Tortoise Stigmochelys pardalis (Bell, 1828) – Africa, to the south of Sahara; (Western) Desert Tortoise Gopherus agassizii (Cooper, 1863) – southwest parts of USA; and Geometric Tortoise Psammobates geometricus (Linnaeus, 1758) – South Africa (Fritz, Havaš, 2007).
In the last several centuries seven species at least have been totally extirpated by humans only on the islands of the Indian Ocean: Aldabrachelys abrupta (Grandidier, 1868) and Aldabrachelys grandidieri (Vaillant, 1885) from Madagascar, Cylindraspis indica (Schneider, 1783) from Reunion, Cylindraspis inepta (Günther, 1873) and Cylindraspis triserrata (Günther, 1873) from Mauritius, Cylindraspis vosmaeri (Suckow, 1798) and Cylindraspis peltastes (Dumáril, Bibron, 1835) from Rodriguez (Fritz, Havaš, 2007).
Because of the excellent taphonomic features, the giant land tortoises are relatively widely represented in the paleontological context. Parham (2006) states that the “Geochelone” complex includes over 25 species. Other specialists list about 48 fossil species, among them: G. atlas, G. becki, G. bolivari, G. ammon, G. ducatelli G. cubensis, G. monensis, G. brachygularis, G. chathamensis, G. crassiscutata, G. darwini, G. depressa, G. eocaenica, G. ephippium, G. farri, G. forstenii G. galapagoensis, G. gigantina, G. guentheri, G. gymnesica, G. hesperotestudo, G. hesterna, G. hoodensis, G. microphyes, G. mlynarskii, G. namaquensis, G. nigrita, G. nordensis, G. oelrichi, G. orthopygia, G. wilsoni, G. pansa, G. phantasticus, G. stromeri, G. turgida, G. incisa, G. wallacei, et al. On the Caribbean there have been described fossil taxa of two subgenera, Monachelys (Williams, 1952) and Chelonoides (Auffenberg, 1974). After Auffenberg (1974) the fossil finds of the giant land tortoises in the Caribbean region are extremely numerous. The Tertiary range of the group is very large. It included North, Central, and South America, Africa, Madagascar, Aldabra, Seychelles, Kazakhstan, Crimea, Moldavia, the Ukraine and Greece.
In the recent Bulgarian herpetofauna, the Chelonians are represented by six species – two terrestrial species (Hermann’s Tortoise (Eurotestudo hermanni (Gmelin, 1789)) and Greek Tortoise (Testudo graeca Linnaeus, 1758)), two terrapins (European pond terrapin (Emys orbicularis (Linnaeus, 1758) and Balkan Terrapin (Mauremys rivulata Valenciennes, 1833)), and two sea turtles (Loggerhead Sea Turtle (Caretta caretta (Linnaeus, 1758) and Green turtle Chelonia mydas (Linnaeus, 1758) (Petrov, 2007).
A total of 22 species/taxa of chelonians have been established so far in the fossil record of Bulgaria, 16 of them fossil and five recent (Boev, in prep.). Among the fossil taxa of a number of sites have been identified: Testudo bulgarica (Amiranashvili, Chkhikvadze 2000); Testudo cf. antigua Schlech, (possibly T. atlas (Falconer, Cautley, 1844) – Z. B.); Testudo aff. marmorum Gaudry, 1862; five taxa of Testudo (Protestudo sp.), two taxa of Testudo sp., all of family Testudinidae Gray, 1825; three taxa of Chelonia fam. indet. of family Cheloniidae Gray, 1825; two taxa, Clemmidopsis cf. sopronensis Boda, 1927 and Emys orbicularis (Linnaeus, 1758) of family Emydidae (Gray, 1825); and two taxa – Trionyx (Amida) capellini bulgaricus Khos. and Trionyx sp. of family Trionychidae Bell, 1828. Numerous fossils of recent E. hermanni, T. graeca and Ch. mydas also have been found.
After a general reorganization of the exposition and the funds of the Regional Historical Museum in the town of Yambol (1999–2000), the well equipped and excellently functioning Nature Department (unapproved by the Ministry of Culture) has been closed. Its rich zoological and paleontological collections (as well as many other of smaller number) and part of its library, collected and managed by Dr. Georgi Ribarov, have been excluded of the Museum funds and through our participation they have been transferred to the National Museum of Natural History in Sofia. Thus, in fact, the NMNHS acquired one of the most considerable completions of its funds during the last several decades. The completion of osteological preserves of recent reptiles, birds and mammals numbered over 400 specimens. Dozens species of them are rare and endangered and now it is extremely difficult to obtain specimens of them even for museum collections.
Among these very valuable materials we accepted also the fossil remains of a giant turtle of highly broken and fragmented plastron and carapace, originating from the sand quarry near Tenevo village (Yambol Region). The tens (64 in number; Figs. 1–3) pieces of the bony sheets, transferred to the NMNHS in April 2001 have shown that the specimen is an adult, completely developed individual of definite size. The find was found in the late 1980s by Dr. G. Ribarov in the fluviatile sand deposits of the Pra-Tundha River. Latter in the same quarry we have found bone remains of a rhinoceros (Rhinocerathidae gen. indet.) and a probosidean mammal (Proboscidea fam. indet.), also presented to the funds of the NMNHS.
The uncovered associated mammalian megafauna (Anancus arvernensus, Stephanorhinus megarhinus, Dolichopithecus sp., Paracamelus sp., Agriotherium cf. sivalensis) allowed to Dr. Nikolay Spassov (NMNHS-BAS) to date these site Early Pliocene (Late Ruscinian) (Spassov, in prep.). The ecological requirements of the established species (mastodon, rhinoceros, primate, camelid, and bear) indicate the presence of abundant grassy vegetation (possibly also arboreal) and plain landscape, which are also preferred environmental conditions to the giant land tortoises.
Initially only tentative we have referred the specimen to Cheloniidae, but the short literature reference and the inspection of the herpetologist. Andrey Stoyanov (NMNHS-BAS) firmly showed that the collected specimen belongs to giant land tortoises (Testudinidae) of the “Geochelone” complex. According his appreciative estimation, the length of the carapace is 1.60–2.00 m and the width – 0.70-1.00 m. No data have been published so far about the discovery of this interesting specimen, which is the goal of present note.
Even highly fragmented, the finds of the uncovered specimen show unambiguously, that they belong to a largest reptile, established so far on the Bulgarian territory. The specimen is the largest terrestrial representative of Class Sauropsida in the collections of the National Museum of Natural History of the Bulgarian Academy of Sciences. As we mentioned above, in the Tertiary the range of the group included also some neighboring regions of Southeast Europe – Crimea, Moldavia, the Ukraine and Greece. It is worthy to note, that the find from Greece, identified as Testudo sp., comes from a locality very close to Bulgarian border, vicinities of Thessaloniki, and it was dated as the same age (Ruscinian), as the Bulgarian tortoise. That is why the discovery of giant land tortoises in Bulgaria is not a sensation. It only completes the knowledge of their Neogene distribution in that part of the continent. On the other hand, their record completes the scanty data on the large terrestrial (mega) herpetofauna as a part of the extinct megafauna of Bulgaria. Having in mind the chronostratigraphical and geographical distribution, as well as the morphological and dimensional features, we tentatively refer the specimen from Tenevo to Testudo ex gr. atlas (Fig. 4).