The Origin of the Bony Shell of Turtles as a Unique Evolutionary Model in Reptiles

Gennady O. Cherepanov


Generally, the bony armor of reptiles consists of separate osteoderms which develop in the dermis independently from the internal skeleton. Such a dermal armor is characteristic of ancient pareiasaurs that are closely related to Testudines. On the basis of this fact it has been assumed that the turtle shell is built up as the fusion of the osteoderms with some elements of the internal skeleton. However, this concept is not confirmed by morphogenetic data. During turtle ontogeny the reduction of the trunk myomeres leads to sinking of the vertebrae and ribs into the dermis. The neural and costal plates of the dorsal disk form as the outgrowths of these endoskeletal bones on inside the dermis. There are no independent superficial ossicles over the general plastral bony primordia in the ventral region of the body. Each plastral plate develops only from a single primordium like the clavicles, interclavicle and gastralia of other reptiles. Most likely, Testudines progressed in a unique evolutionary direction. Their bony shell is mainly the result of modification and consolidation of internal skeletal elements. The real osteoderms develop only on the body margins as connections between the dorsal and the ventral discs.


morphogeny; evolution; Testudinata

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Borkhvardt V. G. (1978), «On the nature of the neural and costal plates in turtles», Vestn. LGU, 15, 7 – 12 [in Russian].

Carroll R. L. (1988), Vertebrate Paleontology and Evolution, W. H. Freeman Press, New York.

Cherepanov G. O. (1984), «On the nature of the plastron anterior elements in turtles», Zool. Zh., 63(10), 1529 – 1534 [in Russian].

Cherepanov G. O. (1988), «The theory of thecal and epithecal ossifications in the context of morphogenetic data», Zool. Zh., 67(5), 729 – 738 [in Russian].

Cherepanov G. O. (1989 – 1992), «New morphogenetic data on the turtle shell: discussion on the origin of the horny and bony parts», Studia Palaeocheloniologica (Salamanca), 3(1), 9 – 24.

Cherepanov G. O. (1994a), «Anomalies of bony carapace in turtles», Zool. Zh., 73(6), 68 – 78 [in Russian].

Cherepanov G. O. (1994b), «The construction of carapace in the family Testudinidae in the connection with the peculiarities of its morphogenesis», Zool. Zh., 73(1), 112 – 121 [in Russian].

Cherepanov G. O. (1995), «Ontogenetic development of the shell in Trionyx sinensis (Trionichydae, Testudinata) and some questions on the nomenclature of bony plates», Rus. J. Herpetol., 2(2), 129 – 133.

Cherepanov G. O. (1996), «Epithecal ossifications in the armor of Trionyx sinensis (Trionychidae, Testudinata): myth or reality? « Zool. Zh., 75(1), 67 – 74 [in Russian].

Deraniyagala P. E. P. (1930), «Testudinate evolution», Proc. Zool. Soc. London, 4, 1057 – 1070.

Gauthier J., Kluge A. G., and Rowe T. (1988), «The early evolution of the Amniota», in: M. J. Benton (ed.), The Phylogeny and Classification of the Tetrapods, Clarendon Press, Oxford, pp. 103 – 155.

Goette A. (1899), «Über die Entwicklung des knöchernen Rückenschildes (Carapax) der Schildkröten», Zs. Wiss. Zool., 66(3), 407 – 434.

Ewert M. A. (1985), «Embryology of turtles», in: Biology of the Reptilia, Vol. 14, Acad. Press, London – New York, pp. 75 – 267.

Ivashchenko M. F. (1987), «Permian parareptiles of the SSSR», Trudy Paleontol. Inst. Akad. Nauk SSSR, 223, 1 – 159 [in Russian].

Ivanov A., Cherepanov G., and Luskevics E. (1995), «Ontogenetic development of antiarch dermal ossifications», Geobios, M. S. 19, 97 – 102.

Kälin J. A. (1945), «Zur Morphogenese des Panzers bei den Schildkröten», Acta Anat., 1(1/2), 144 – 176.

Laurin M. and Reisz R. R. (1995), «A reevaluation of early amniote phylogeny», Zool. J. Linn. Soc. (London), 113, 165 – 223.

Lee M. S. Y. (1995), «Historical burden in systematics and the interrelationships of ‘parareptiles’», Biol. Rev., 70, 459 – 547.

Lee M. S. Y. (1996), «Correlated progression and the origin of turtles», Nature, 379, 812 – 815.

Meylan P. A. (1987), «The phylogenetic relationship of soft-shelled turtles (family Trionychidae)», Bull. Am. Nat Hist., 186(1), 1 – 96.

Młynarski M. (1976), «Testudines», in: O. Kuhn (ed.), Handbuch der Palaeoherpetologie, Teil 7, Gustav Fischer Verlag, Stuttgart – New York, pp. 1 – 130.

Procter J. B. (1922), «A study of the remarkable tortoise, Testudo loveridgii Blgr., and the morphogeny of the chelonian carapace», Proc. Zool. Soc. London, 34, 483 – 526.

Romer A. S. (1956), Osteology of the Reptiles, Univ. of Chicago Press, Chicago.

Romer A. S. (1968), Notes and Comments on Vertebrate Paleontology, Univ. of Chicago Press, Chicago.

Ruckes H. (1929), «Studies of chelonian osteology», Ann. N. Y. Acad. Sci., 31, 31 – 120.

Schmidt W. J. (1916), «Über den dermalen Ursprung der neuralplatten des Schildkrötencarapax», Zool. Anz., 47, 9 – 14.

Sikorska-Piwowska Z. (1986), «Comments on the phylogeny of chelonians», in: Stud. Herpetol. Proc. Eur. Herpetol. Meet., Prague, pp. 67 – 70.

Sukhanov V. B. (1964), «Subclass Testudinata», in: A. K. Rozhdestvensky and L. P. Tatarinov (eds.), Principals of Paleontology. Amphibians, Reptiles, and Birds, Moscow, pp. 354 – 438 [in Russian].

Suzuki H. K. (1963), «Studies on the osseous system of the slider turtle», Ann. N.Y. Acad. Sci., 109(1), 351 – 410.

Vallen E. (1942), «Beiträge zur Kenntnis der Ontogenie und der vergleichenden Anatomie des Schildkrötenpanzer», Acta Zool. (Stockholm), 23(1/3), 1 – 127.

Walker W. F. (1973), «The locomotor apparatus of Testudines», in: C. Gans and T. S. Parsons (eds.), Biology of the Reptilia, Vol. 4, Acad. Press, London – New York, pp. 1 – 100.

Williams E. E. and McDowell S. B. (1952), «The plastron of soft-shelled turtles (Testudinata, Trionychidae): A new interpretation», J. Morphol., 90(2), 263 – 279.

Yntema C. L. (1968), «A series of stages in the embryonic development of Chelydra serpentina», J. Morphol., 125(2), 219 – 251.

Zangerl R. (1939), «The homology of the shell elements in turtles», J. Morphol., 65, 383 – 406.

Zangerl R. (1969), «The turtle shell», in: C. Gans, A. d’Bellairs, and T. S. Parsons (eds.), Biology of the Reptilia, Vol. 1, Acad. Press, London – New York, pp. 311 – 339.



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