Batsch, 1788
Tortoises
Recognition
The terrestrial tortoises compose the family Testudinidae, which is second only to the Bataguridae in total number of living species (55—when treating the Galápagos tortoises as separate species). Today its members are found primarily in the tropical portions of Africa, Madagascar, Asia, South America, Aldabra Atoll, Seychelles Islands, and the Galápagos Archipelago. However, species extend into southern Europe (3), western Asia (1), and southern North America (4). The fossil record shows tortoises were much more widespread in the past, occurring in northern Europe including Great-Britain, central Asia, the West Indies, and in North America to southern Canada. Many islands in the Indian Ocean also had endemic species which have become extinct in modern times through human exploitation. Fossil tortoises date from the early Eocene: Geochelone (Manouria) majusculus from New Mexico deposits and Testudo (?) comptoni from the Isle of Sheppey, England. By the end of the Eocene, tortoises of several other genera appeared in North America: Geochelone (Manouria) gilmorei (= Hadrianus robustus), G. (M.) utahensis, G. (Cymatholcus) longus, Stylemys uintensis in Utah; G. (M.) corsoni in Wyoming; and G. (C.) schucherti in Alabama. In Europe, Testudo corroyi, T. (?) castrensis, and T. doduni appeared in France; G. (M.) eocaenica in Germany; G. (M.) obailiensis inhabited the USSR (Georgia); G. (G.) beadnelli, G. (G.) isis in Africa (Egypt); G. (M.?) ammon, G. (M.) insolitus, G. (?) ulanensis, Indotestudo kaiseni in Asia (Mongolia); Kansuchelys (?) chiayukuanensis; and Sinohadrianus (?) sichuanensis from China and Japan. Many islands in the Indian Ocean also had endemic species which have become either extinct or extirpated in the wild, some in the distant past and others in modern times (see various reviews by Arnold and Bour). Among living tortoises, Manouria emys and M. impressa are considered to be most primitive, as they share a number of derived characters with some of the oldest fossil species; thus, they are placed in a separate genus. Additional information on fossil tortoises may be obtained from Williams (1950b, 1952), Mlynarski (1969), and Auffenberg (1974).
Tortoise skulls are short to moderate in length, but very different from those of the Emydidae and Bataguridae (Gaffney, 1979b). The temporal region is widely emarginated posteriorly and the squamosal is not in contact with the parietal. The frontal bone may or may not enter the orbit, and the postorbital is reduced (rarely absent) and narrower than that found in emydids. The maxilla rarely touches the quadratojugal and the quadrate is usually closed posteriorly, completely surrounding the stapes. Premaxillae meet dorsally with descending processes to form a hooklike upper jaw, as in the Kinosternidae. The triturating surface of the upper jaw is moderately developed with or without a medial ridge of varying development on the maxilla, but usually not on the premaxilla (Gopherus has a medial premaxillary ridge). No splenial bone is present. The carapace is usually highly arched or domed, and contains a movable posterior hinge in the genus Kinixys. A medial keel may be present in juveniles, but disappears with age in all species. The anterior neural bones alternate in shape between square (4-sided) and octagonal (8-sided) in all genera but Manouria. Dorsal rib heads are small and often vestigial. The seams separating the pleural and marginal scutes lie over the costal-peripheral bone sutures. Carapaceandplastron are firmly sutured at the bridge, and a distinctive anterior bony ridge is present on the inside of the plastron. The plastron is usually rigid, but is hinged (differently) in Pyxis and most Testudo. Mesoplastral bones are absent, as also is an intergular scute. Infra- or submarginal scutes are present only in Kinixys. The shell is poorly ossified in the genus Malacochersus. Limbs are developed for walking on land and supporting much weight and/or for digging. Toe webbing is absent, and there are no more than two phalanges in any digit; the trochanteric fossa of the femur is narrowed by the close apposition of the trochanters. In the pelvic girdle, the pubis normally contacts the ischium of the same side below the thyroid fenestra; ventral cartilages are usually absent in adults and the pubis and ischium of the two sides can meet. The family is composed of 11 genera and 55 species.