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A JUVENILE TANYSTROPHEUS SP. (PROTOROSAURIA, TANYSTROPHEIDAE) FROM THE MIDDLE TRIASSIC OF GUIZHOU, CHINA
- LI Chun
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2007, 45(1):
37-42.
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An incomplete skeleton(IVPP V 14472) of protorosaur, in which only the last five neck vertebrae, the trunk and the forelimbs are preserved(Fig.1), is identified as a juvenile Tanystropheussp. based on the unique structure of the cervical vertebrae: neural arch poorly developed; centrum obviously elongate, ratio of the length to height large (from 4.43 to 8.98, similar to Tanystropheus but distinctly larger than Dinocephalosaurus orientalis (Table 1,2). The total number of cervical vertebrae is assumed as 12, as in Tanystropheus); double-headed cervical rib extremely long and slender, extending backwards across 2～3 cervical vertebrae. Most elements of the shoulder girdle overlap each other. Both of the scapula and coracoid are plate shaped, and there are a lot of tiny humps on the surface of the scapula. The distal end of the interclavicle somewhat triangle in shape; fourcarpals ossified (only 3 preserved in the left forelimb); digital formula of the forelimb is2-3-4-4-3(Fig 1). The distal end of the rib expanded. The shape of the ilium and the ischium is the same as that of Tanystropheus longobardicus. Some slight difference between V 14472 and T. longobardicus was probably due to development stages. For example, the longest cervical vertebra of V14472 is the 10h one, while in T. longobardicus, the 9h is the longest one. Along the neck and in the abdomen part of the specimen, there are some tiny bones that look like the digested draft.A few of them could be recognized as the tooth or vertebral centrum of the fish. In contrast to the terrestrial and insectivore at juvenile stages, as suggested by Wild (1973),V 14472 should be seen as a marine predator based on the number and the structure of the carpus. Derived sauropterygian and marine protorosaur developed the extremely long neck by different ways. With very short centrum and cervical rib, some plesiosaurs had 60~70 verte-brae. In Tanystropheus and Dinocephalosaurus, both the individual centrum and the cervical rib are greatly elongate, while the number of neck vertebrae only moderately increased (12 for Tanystropheus and 25 for Dinocephalosaurus). As bounded by 2～3 cervical ribs in each side, the intervertebral joint must be fixed and the whole neck must be stiffened. Marine reptiles with such an unskillful long neck, not only the protorosaur but also some archosaurian(Li et al.,2006), would have adopted the"suction"way to catch the prey(Li et al.,2004). The new material(V 14472) was found from the Middle Triassic(Falang Formation, Ladinian) of Chajiang, Guizhou Province, southwestern China. This is the first record of Tanystropheus outside Europe and Middle East(Rieppel,2001), confirming a close relationship between eastern and western Tethyan fauna province during the middle Triassic. The affinity between the two regions is also represented by some other marine reptile groups, including Lariosaurus(Rieppel et al.,2003), Nothosaurus(Li and Rieppel,2004), askeptosaurid(Liu and Rieppel,2005) and cyamodontoid placodont(Li,2000; Li and Rieppel,2002).
