1902 Encyclopedia > Tortoise

Tortoise




TORTOISE. Of the three names generally used for this order of reptiles, viz., Tortoise, Turtle, and Terrapin, the first is derived from the old French word tortis, i.e., twisted, and was probably applied first to the common European syiecies on account of its curiously bent fore-legs. Turtle is believed to be a corruption of the same word, but the origin of the name terrapin is unknown : since the time of the navigators of the 16th century it has been in general use for freshwater species of the tropics, and especially for those of the New World. The name tortoise is now generally applied to the terrestrial members of this group of animals, and that of turtle to those which live in the sea or pass a great part of their existence in fresh water.

Tortoises and turtles constitute one of the orders of Reptiles, the Chelonia. They are characterized by having the trunk of the body incased in a more or less ossified carapace, which consists of a dorsal more or less convex portion, and of a flat ventral one, the so-called plastron. These portions are generally more or less firmly united on the side, but leave a wide opening in front through which the head and neck and the fore-limbs protrude, and one behind for the tail and hind-limbs. The dorsal carapace is (with the exception of Sphargis) formed by the dorsal vertebra;, by the ribs which are so much expanded as to form sutures with each other, and by a number of lateral dermal ossifications (marginals). The plastron consists of from eight to eleven more or less dilated dermal bones, the sternal elements of higher Vertebrata being absent. This osseous case or shell receives in its interior the organs of the chest and abdomen, the humeral and pelvic bones, and the muscles for the humerus and femur. In many species, especially those of the family Testudinidx, or tortoises proper, the neck and head and the limbs can be withdrawn within the shell, the cervical and the proximal caudal vertebrae retaining their mobility. In the majority of Chelonians the osseous shell is covered with a hard epider-moid coat, which is divided into large symmetrical plates (commonly called " tortoise-shell" in those species from which the article of commerce is obtained), which can be detached from the underlying bones. These epidermoid plates do not correspond in arrangement or extent with the bones of the carapace ; they vary considerably in form, and are therefore generally noticed in the descriptions of species. Their arrangement and terminology may be learned from the accompanying illustrations (figs. 1, 2).

The integuments of the head, neck, tail, and limbs are either soft and smooth or tubercular or scaly, the tubercles and scales having frequently an osseous nucleus.

Other parts also of the skeleton show remarkable peculiarities, so that the sometimes very fragmentary remains of Chelonians can almost always be recognized as such. All the bones of the skull are suturally united, with the exception of the mandible and hyoid bone ; the dentary portion of the mandible consists of one bone only. The pectoral arch is composed of the scapula, with which the precoracoid is united, and the coracoid. Clavicles (epi-plastra) are represented by the anterior elements of the plastron. Two pairs of limbs are invariably present.

All Chelonians possess a tail, which is generally short, but sometimes elongate, and always provided with strong muscles at the base. No Chelonian possesses teeth ; but their jaws are provided with horny sheaths, with hard and sharp edges, forming a beak like that of a parrot.

The number of Chelonians hnown at present may be estimated at about 220, the freshwater species being far the most numerous, and abundant in well-watered districts of the tropical and subtropical zones. Their number and variety decrease beyond the tropics, and in the north they disappear entirely about the 50Li parallel in the western and about the 56th in the eastern hemisphere, whilst in the southern hemisphere the terrestrial forms seem to advance to 36° S. lat. only. The marine turtles, which are spread over the whole of tno equatorial and subtropical seas, sometimes stray beyond those limits. As in other orders of Reptiles, the most specialized and the largest forms are restricted to the tropics (with the exception of Macroclemmys), but, unlike lizards or snakes, Chelonians

Fig. 1.

Fig. 2.
FIGS. 1, 2.—Shell of Testudo partialis, to show the divisions of the integument, which are marked by entire lines, and of the osseous carapace, these being marked by dotted lines. Fig 1. Upper, or dorsal aspect. Fig. 2, Lower or ventral aspect.
Dermal Scutes:—co, costals; v, verfebrnls; m, marginals: g, gulars; pg, post-gulars; p, pectorals; ab, abdominals; pa, prseanols; an, anals.
Bones of the Carapace:—co', costals; ne, neurals; nu, nuchal; py, pygal; m\ marginals; ent, entoplastron, ep, epiplastron; hyo, hyoplastron; hyp, hypo-plastron; xyp, xyphiplastron.

are unable to exist in sterile districts or at great altitudes. Chelonians are strictly animals of plains, or at least of low country.

Chelonians show a great divergence in their mode of life,—some living constantly on land, others having partly terrestrial partly aquatic habits, others again rarely leav-ing the water or the sea. The first-mentioned, the land tortoises proper, have short club-shaped feet with blunt claws, and a very convex, heavy, completely ossified shell. In the freshwater forms the joints of the limb bones are much more mobile, the digits distinct, armed with sharp claws, and united by a membrane or web ; their shell is less convex, and is flattened, and more or less extensive _areas may remain cartilaginous to lessen its specific gravity. As a rule, the degree of development of the interdigital web and of convexity of the shell indicates the prevalence of aquatic or terrestrial habits of a species of terrapin. Finally, the marine turtles have paddle-shaped limbs re-sembling those of Cetaceans.

Land tortoises are sufficiently protected by their carapace, and therefore have no need of any special modification of structure by means of which their appearance would be assimilated to the surroundings, and thus give them additional security "rom their enemies. These, however, are but few in number : the large cats of South America are said to be able to tear them out of the shell with their claws ; and the ancient tale of jEschylus having been killed by a tortoise carried aloft by an eagle and dropped on the head of the unfortunate poet seems to be founded on the fact that tortoises are a favourite prey of the Liimmergeyer (Gypaelus), which has the habit of dropping them from a height on rocks in order to break the shell. On the other hand, among the carnivorous terrapins and freshwater turtles instances of protective resemblance are not scarce, and may even attain to a high degree of specialization, as in Chelys ; their shells offer them less protection, and their enemies (crocodiles and alligators) are more numerous ; they also require this special provision to enable them to approach or seize their prey with greater ease. The colours of land tortoises are generally plain or in simple patterns, whilst those of many terrapins are singularly varied, bright, and beautiful.

Chelonians are diurnal animals ; only a few are active during the night, habitually or on special occasions, as, for instance, during oviposition. Land tortoises are slow in all their movements, but all kinds living in water can execute extremely rapid motions, either to seize their prey or to escape from danger. All Chelonians are stationary, residing throughout the year in the same locality, with the exception of the marine turtles, which periodically migrate to their breeding-stations. Species inhabiting temperate regions hibernate.

Chelonians possess great tenacity of life, surviving injuries to which other Reptiles would succumb in a short time. The heart of a decapitated tortoise continues to beat for many hours after every drop of blood has been drained from the body, and the muscles of the trunk and head show signs of reflex action twenty-four hours after the severance of the spinal cord. The longevity of tor-toises is likewise a well-known fact, to which reference will again be made.

Land tortoises, a few terrapins, and some of the marine turtles are herbivorous, the others carnivorous, their prey consisting chiefly of fish, frogs, and other small aquatic animals.
All Chelonians are oviparous, and the eggs are generally covered with a hard shell.
In the system proposed by Dumeril and Bibron, and afterwards modified by Gray and Strauch, the Chelonians are arranged according to their mode of life, and divided into terrestrial, paludine, fluviatile, and marine forms. However natural such an arrangement may appear at first, a more careful examination proves it to be (as all arrange-ments based solely upon the mode of life) at variance with the structural affinities, whether the recent forms alone be considered or the fossil as well. The division of the bulk of the order into Cryptodira and Pleurodira, as suggested by Agassiz, Cope, and Biitimeyer, was a decided progress, as is also the elimination of the suborders Atheca and Trionychoidea recently proposed by Cope and Baur.

The order of Chelonians may then be divided into the following suborders and families : —

SUBORDER I. ATHECAE.
Vertebra and ribs free, separated from a bony exoskeleton.
Family 1. SPHARGIDAE. Limbs paddle-shaped, clawless; phalanges without condyles. Plastron reduced to an annular series of eight small bones. Exo-skeleton consisting of numerous small bony plates arranged like mosaic. Pelagic. Genus: Dermatochelys (Spliargis).
Fossil genera: Psephophorus (Pliocene), Protosphargis (Cretaceous), Protostega (Cretaceous), Psephoderma? (Triassic).
SUBORDER II. TESTUDINATA, ' Dorsal vertebra and ribs immovably united and expanded into bony plates forming a carapace, which is bordered by a complete series of marginal bones. Epiplastra (clavicles) in contact with hyoplastra; entoplastron (interclavicle), if present, oval, rhom-boidal, or f-shaped. Sacral and caudal ribs articulating with the centrum and the neural arch. Digits with not more than three phalanges.
SERIES A. CRYPTODIRA.
Neck retractile by a sigmoid curve in a vertical plane. Pelvis not anchylosed to the carapace and plastron. Rarely one or two epidermic scutes (intergular) in addition to the normal six pairs.
GROUP A. Digitata. Digits short or moderately elongate; phalanges with condyles; claws four or five. Neck completely retractile.
Family 1. TESTUDINIDAE.
Plastral bones nine. Nuchal bone without costiform processes. Carapace with epidermic scutes. Caudal vertebra proccelous. Tropical and temperate zones, with the exception of Australia.
Recent genera: Dermalemys, Balagur, Clemmys, Pangs/mra, Geoemyda, Cycle-?nys, Emys, Cistudo. Manouria, Testudo, Homopus, Cinyxis, Pyxis.
Fossil genera: Eurysternum (Jurassic), Chitracephalus (Cretaceous), Adocus (Cretaceous), Palteodielys (Miocene), Ptychogaster (Miocene), Colossochelys (Pliocene).
Family 2. PLATYSTERNIDAE.
Plastral bones nine. Nuchal bone without costiform processes. Carapace with epidermic scutes. Caudal vertebra mostly opistho-ccelous. Indian region.
Genus: Platyslernum.
Family 3. BAENIDAE.
Plastral bones eleven, mesoplastra being present. Nuchal bone without costiform processes. Carapace with epidermic scutes. Caudal vertebra? opisthoccelous.
Fossil genera: Platychelys (Jurassic); Baena (Eocene).
Family 4. CHELYDRIDAE.
Plastral bones nine. Nuchal bone with long costiform processes, extending below the marginals. Carapace with epidermic scutes. Caudal vertebra? mostly opisthoccelous. Northern and tropical American regions.
Recent genera: Chelydra, Macroclemmys.
Fossil genus: Tretosternum(Cretaceous),
Family 5. STAUROTYPIDAE (Boulenger), Plastral bones nine. Nuchal bone with short costiform pro-cesses, extending below the marginals. Carapace with epidermic scutes. Caudal vertebra proccelous. . Central-American district. Genera: Staurotypus, Claudius.
Family 6. CINOSTERNIDAE.
Plastral bones eight, the entoplastron being absent. Nuchal bone with short costiform processes, extending below the marginals. Carapace with epidermic scutes. Caudal vertebra proccelous. Northern and tropical American regions.
Genera: Aromockelys, Cinosternum.
Family 7. PSEUDOTRIONYCHIDAE (Boulenger). Shell without epidermic scutes. Fossil genera : Pseudotnonyx and Anoslira (Eocene).
GROUP B. Pinnata. Limbs paddle-shaped; phalanges without condyles; claws one or two. Neck imperfectly retractile; cervical Vertebra short, mostly articulated by amphiarthrosis.
Family 8. CHELONIDAE.
Plastral bones nine. Nuchal without costiform processes. Carapace with epidermic scutes. Hyo- and hypo-plastra not meet-ing mesially. Pelagic.
Recent genera : Che/one, Caouana, Carella.
Fossil genus : Puppigerus (Miocene and Eocene)
SERIES B. PLEURODIRA.
Neck not retractile, bending laterally. Pelvis anchylosed to the carapace and plastron. When epidermic scutes are present, one or two intergulars in addition to the normal plastral scutes.
Family 1. CHELYDlDAE.
Plastral bones nine. Carapace with epidermic scutes. Limbs with four or five claws. Australian and tropical American regions.
Recent genera: Platemys, Chelymys, Etseya, Chelodina. Ilydraspis, Hydro-medusa, Chelys.
Fossil genera: Plesiockelys (Jurassic), Craspedochehjs (Jurassic), Idiochelyi (Jurassic), Nolomorpha (Eocene).
Family 2. PELOMEDUSIDAE.
Plastral bones eleven, mesoplastra being present. Carapace with epidermic scutes. Limbs with four or five claws. African and tropical American regions.
Recent genera: Pelomedusa, Slernothients, Dumerilia, Podocnemis, Pelto-cephalus.
Fossil genera: Pleurosternum (Cretaceous, Eocene), Bothremys (Cretaceous), Taphrosp/iys (Cretaceous).
Family 3. CARETTOCHELYDIDAE. Plastral bones nine. No epidermic scutes on the shell. Limbs paddle-shaped, with only two claws. New Guinea. Genus: Careitochelys.
Family 4. MIOLANIIDAE (Boulenger). Caudal vertebra; opisthoccelous ; tail long and encased in a bony sheath. Australia. Fossil genus : Miolania (Pleistocene).
SUBORDER III. TRIONYCHOIDEA. Dorsal vertebra; and ribs immovably united, forming a carapace; no pygal plate; marginal plates absent or forming an incomplete series. Plastron formed of nine bones, epiplastra separated from the hyoplastra by the entoplastron, which is j\-shaped, without longitudinal process. Sacral and caudal ribs attached to transverse processes of the neural arch. Fourth digit with four or five phalanges.
Family 1. TRIONYCHIDAE. No epidermic scutes. Limbs with three claws. Indian, African, and American regions. Genera: Chitra, Heptathyra, Trionyx, Cyclanosteus, Emyda.

We add a few notes on such of the genera enumerated in this synopsis as have some special interest attached to them, either from a scientific or an economic point of view.

The family Sphargidae is represented in the recent fauna by a single species, Bermatochelys or Sphargis coriacea, the Leathery Turtle, the range of which extends over the tropical and subtropical seas of both hemispheres, and which occasionally strays into the northern parts of the Atlantic, its occurrence on the British coast having been recorded three or four times within the last century. It differs from all other Chelonians by its carapace being formed by ossifications of the skin only. Neither the vertebra nor the ribs enter into its formation; the latter remain free, and are not particularly dilated. During the life of the animal the carapace ia flexible like thick leather, the bony deposits being arranged like mosaic, with several longitudinal ridges of larger osseous tubercles. The limbs are, as in other marine turtles, paddle- or fin-shaped, the anterior much longer than the posterior, and all destitute of claws. This turtle is probably the largest living Chelonian, exceeding 6 feet in length. The names Testudo lyra, Sphargis mercurialis, &c, have reference to the myth that the shell of this or some other turtle was used by Mercury in his construction of the lyre.

The family Testudinidae is composed of an unbroken series, from thoroughly aquatic freshwater tortoises like Dermalemys and Batagur to the tortoises which live exclusively on land and are perfectly helpless in water. In the Central-American genus Der-matemys the digits are very broadly webbed, the epidermic scutes are thin, and the nose is much produced,—characters which, together with the strong depression of the shell, give these terrapins some-what the aspect of the freshwater turtles or Trionychidse. They feed exclusively upon leaves, grass, and especially fruit, and are eaten by the natives. Of the freshwater tortoises of the Old World the most thoroughly aquatic are the Batagurs, which inhabit the East Indies, and attain to a length of 2 feet. Like their American representative, Bermatemys, they are essentially herbivorous, ami their flesh is eaten. The genus Clemmys is extremely abundant in species, most of which are of small size, and elegantly ornamented with symmetrical markings of bright colour. The majority of the species occur in North America and Mexico, and are of amphibious habits. Only one species," C. leprosa, inhabits southern Europe. A second European species belongs to the genus Emys, E. orbi-cularis, which, towards the end of the Quaternary period appears to have been distributed over a great part of northern Europe, remains having been found in peat in England, Belgium, Denmark, and Sweden. Its habitat is now restricted to southern Europe, south-western Asia, and north-western Africa; but singularly it has survived in a few isolated northern stations, for instance, in the neighbourhood of Berlin and Königsberg, although it is there, on the verge of extinction. The mobility of the lobes of the plastron, which distinguishes Emys from Clemmys, is carried a degree further in the North-American genus Cistudo, the Box Tortoise; this terrapin possesses a hinge in the plastron, rendering its anterior-and posterior portions movable, and converting them into lids by which the openings of the shell can be completely closed when the head and limbs are retracted. A similar protective apparatus exists in the tortoises of the genus Cinosternum. In the African terrestrial genus Cinyxis it is the posterior portion of the carapace that is movable, and separated from the anterior by a hinge. True land tortoises, Testudo, occur in Africa, southern Europe, southern Asia, South America, and the southern parts of North America. Those best known in Europe are Testudo greeca and the Moorish Tortoise, Testudo mauritanica, large numbers of which are imported into the United Kingdom, chiefly from Morocco. But the most interesting are the gigantic tortoises which formerly inhabited in extreme abundance the Mascarene and Galapagos Islands, and are now on the verge of extinction, or have actually become extinct. At the time of their discovery those islands were [ uninhabited by man or any large mammal; the tortoises, therefore, enjoyed perfect security; and this, as well as their extraordinary degree of longevity, accounts for their enormous size and their large numbers. They could be captured in any quantity with the greatest ease within a few days, and proved to the ships' companies who during their long voyages had to subsist mainly on salt provisions a most welcome addition to their table. They could be carried in

FIG 4 Loggerhead (Caouana earetta)

the hold of a ship, without food, for months, and were slaughtered as occasion required, each tortoise yielding, according to size, from 80 to 300 pounds of excellent and wholesome meat. Under these circumstances the numbers of these helpless creatures decreased so rapidly that in the beginning of this century their extermination was accomplished in the Mascarenes, and now only a few remain in a wild state in Aldabra and in some of the islands of the Gala-pagos group. Singularly, the majority of these islands were in-habited each by one or more peculiar forms, specifically distinct

FIG. 5.—Green Turtle (Chelonia viridis).

from those cf the other islands. A large male specimen from Aldabra, which was imported into London some years ago, weighed 870 lb, and, although known to have ocen more than eighty years old, was still growing at the time of its death. There is no evidence to show that any of these tortoises were indigenous in the Seychelles; the speci-mens kept there in a semi-domesticated state have been either directly imported from Aldabra or are the descendants of imported individuals.

The family of Chelydridae includes freshwater tortoises, which are known under the names of Snappers or Alli-gator Terrapins (fig. 3), on account of their ferocity and long compressed crested tail. They are now confined to North America east of the Rocky Mountains, Central America, and north-west South America, but remains of two species of Chehjdra, closely related to their recent representative, have been found in the Oligocene and Miocene of central Europe. A second genus, closely allied to Cltelydra, Macroclcmmys temminckii, the shell of which attains to a length of 3 feet, and which is the largest known freshwater Chelonian, is restricted to the river-systems tributary to the Gulf of Mexico.

The family of Cinosternidae contains a rather large number of small-sized species, distributed from the northern parts of the United States to the northern parts of Brazil. They are of amphibious habits. The front and hind lobes of the plastron are movable, and in certain species of Cinosternum the animal can completely shut itself up in its shell.
The Chdonidas, or marine turtles, contain but few species, which are referred to three genera,—Caouana, Chdone, and Carctta. Their limbs are wholly modified into paddles, by means of which they can propel themselves with extraordinary rapidity through the water, but which are entirely unfit for locomotion on land, where the progress of these animals is as awkward as that of a seal. The toes are enclosed in a common skin, out of which only one or two claws project. The carapace is broad and much de-pressed, so that when the turtles are surprised on shore and turned

FIG. G.—Ilawksbill Turtle (Caretta inibrieata).

over on their back, they cannot regain their natural position. Their capture forms a regular pursuit wherever they occur in any numbers, Comparatively few are caught in the open sea, others in stake nets, but the majority are intercepted at well-known periods and localities where they go ashore to deposit their eggs. These are very numerous, from 100 to 250 being produced by one female, and buried by her in the sand; they are eagerly searched for and eaten. Some of the marine turtles are highly esteemed for the delicacy of their meat and of the gelatinous skinny parts of their neck and fins; others yield oil, and others again the tortoise-shell of commerce. Probably the largest of these marine turtles is the Loggerhead (Caouana), which possesses fifteen vertebral and costal shields, and occurs in the Atlantic as well as in the Indian Ocean (fig. 4). It is carnivorous, feeding on fish, molluscs, and crustaceans, and not esteemed as food, although it is eaten by the nat've fishermen. A great part of the turtle-oil which finds its

way into the market is obtained from the Atlantic species of this genus; also tortoiseshcll of an inferior quality is obtained from it.

The Green Turtle (fig. 5) which yields the mate-rials for the celebrated soup, belongs to the genus Chelonia; it is distinguished from Caouanct by having thirteen ver-tebral and costal shields only, which are not im-bricate. These animals are herbivorous, feeding ou marine Algse only; they occur in the Indo-PacificandAtlantic; and, although several species have been distinguished, they all may possibly be referable to one only. The turtle imported into conies chiefly from the West Indies. Instances are recorded of the flesh of this species having acquired poisonous qualities. The Hawksbill Turtle, Carctla (tig 6), sc named from its rather elongate and compressed curved upper jaw, does not reach the same size as the other turtles, and is readily recognized by the thirteen imbricate scutes of its carapace. It seems to be more abundant in the Indian than in the Atlantic Ocean, but plentiful only in certain localities. As, however, these turtles always re-sort to the locality where they were born, or where they have been wont to propagate their kind, and as their capture is very profitable, they become scarcer and scarcer at places where they are known to have been abundant formerly. If the plates of tortoise-shell are detached from the animal when decom-position has set in, their colour becomes clouded and milky, and hence the cruel expedient is resorted to of suspending the turtle over fire till heat makes the shields start from the bony part of the cara-pace, after which the creature is permitted to escape to the water. There is no doubt that turtles thus allowed to escape to the water after such an operation may survive; but it is very improbable that the epidermal shields are ever sufficiently regenerated to be fit for use. At Celebes, whence the finest tortoiseshcll is exported to China, the natives kill the turtle by blows on the head, and immerse the shell in boiling water to detach the plates; dry heat is only resorted to by the unskilful. The natives eat the flesh of this turtle, but it is unpalatable to Europeans; the eggs, however, are regarded as equal to those of the other turtles.

Of the family Chelydidae the most remarkable type is the Matamata, Chelys fimbriata, a native of the Guianas and northern Brazil (fig. 7). In its strongly depressed and flat head, long tube-like snout, weak jaws, minute eyes, skinny tentacles, it bears a striking similarity to the Surinam toad, Pipa americana, which inhabits the same countries. The neck is very broad and depressed, and fringed with foliated tentacles, floating in the water like some vegetable growth, whilst the rough bossed carapace resembles a stone,—an appearance which evidently is of as great use to this creature in escaping the observation of its enemies as in alluring to it unsuspicious animals on which it feeds.

The family of Carettochelydidae contains a single genus, Caretto-chelys, quite recently discovered in the Fly river, New Guinea, and exhibiting a remarkable combination of characters. Its limbs are formed very much like those of the marine turtles, whilst the shell lacks epidermic scutes, as in the Trionychidse.

In the freshwater turtles, or Trionychidae (figs. 8 and 8), the cara-pace is reduced to a flat disk, which is covered with soft skin. The neck and limbs can be lodged under the broad skinny borders of the carapace; also the plastron is very imperfectly ossified, and some-times dilated into large flexible lobes which may cover the limbs. The latter are much flattened and broadly webbed, and only the three inner toes armed with claws. The jaws are concealed under broad, fleshy lips, the nose projecting like a short proboscis. These turtles are carnivorous, and very ferocious; when they want to bite or seize their prey they project their neck and head with lightning rapidity. They are well known on the upper Nile, Euphrates, Ganges, Yangtse-kiang, and Mississippi, and, indeed, distributed over all the large fresh waters of the geographical regions to which these rivers belong. Some of the species exceed a length of 3 feet. In the United States, where two species, Trionyx mulicns and Trionyx ferox, occur, the flesh of the latter is said to be most delicate to eat, far surpassing in flavour that of the green turtle. (A. C. G.)

Footnotes

The more important works on this order of Reptiles have been enumerated in the article REPTILES, vol. xx. p. 440.
Only the more important and best known of the extinct genera are admitted into this synopsis.







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