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The forefin of Chensaurus chaoxianensis (Ichthyosauria) shows delayed mesopodial ossification

Published online by Cambridge University Press:  20 May 2016

Ryosuke Motani  and
Hailu You
Ryosuke Motani
Affiliation:
Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario, M5S 3G5 Canada
Hailu You
Affiliation:
Department of Geology, University of Pennsylvania, Hayden Building, Philadelphia 19104
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Abstract

The hitherto poorly known forefin of Chensaurus chaoxianensis (Ichthyosauria) from the Lower Triassic (Spathian) is redescribed on the basis of the holotype and two new specimens. The humerus resembles that of Utatsusaurus hataii but is distinctive in having an emarginated anterior margin. The anteroproximal prominence of the radius is well developed, unlike that of other ichthyosaurs. All three specimens have five metacarpals and many phalanges, but only three carpals, which are identified as the ulnare, intermedium, and fourth distal carpal. These specimens show that delayed mesopodial ossification occurred in ichthyosaurs, at least in an early evolutionary stage. Because delayed mesopodial ossification is common among diapsids and is unknown in Jurassic ichthyosaurs, it was lost during the evolution of the Ichthyosauria. The osteogenic developmental axis appears to have continued into the fourth digit, as in other amniotes. The ossification pattern provides conclusive evidence to support the suggestion that the basal element of the fifth digit in Early Triassic ichthyosaurs is a metacarpal, rather than a carpal.

Type
Research Article
Information
Journal of Paleontology , Volume 72 , Issue 1 , January 1998 , pp. 133 - 136
Copyright
Copyright © The Paleontological Society 

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References

Brinkman, D. B., Zhao, X., and Nicholls, E. L. 1992. A primitive ichthyosaur from the Lower Triassic of British Columbia, Canada. Palaeontology, 35:465–474.Google Scholar
Caldwell, M. W. 1994. Developmental constraints and limb evolution in Permian and extant lepidosauromorph diapsids. Journal of Vertebrate Paleontology, 14:459–471.Google Scholar
Caldwell, M. W. In press a. Limb ossification patterns in the ichthyosaur Stenopterygius, with a discussion of the proximal tarsal row of ichthyosaurs and other neodiapsid reptiles. Zoological Journal of the Linnean Society.CrossRefGoogle Scholar
Caldwell, M. W. In press b. Modified perichondral ossification and the evolution of paddle-like limbs in ichthyosaurs and plesiosaurs. Journal of Vertebrate Paleontology.Google Scholar
Carroll, R. L. 1988. Vertebrate Paleontology and Evolution. W. H. Freeman and Company, New York, 698 p.Google Scholar
Chen, L.-Z. 1985. Ichthyosaurs from the Lower Triassic of Chao County, Anhui. Regional Geology of China, 15:139–146. (in Chinese)Google Scholar
Johnson, R. 1977. Size independent criteria for estimating relative age and the relationship among growth parameters in a group of fossil reptiles (Reptilia: Ichthyosauria). Canadian Journal of Earth Sciences, 14:1916–1924.Google Scholar
Mazin, J.-M. 1986. A new interpretation of the forefin of Utatsusaurus hataii (Reptilia, Ichthyopterygia). Paläontologische Zeitschrift, 60:313–318.Google Scholar
Mazin, J.-M., Suteethorn, V., Buffetaut, E., Jaeger, J.-J., and Helmcke-Ingavat, R. 1991. Preliminary description of Thaisaurus chonglakmanii n. g., n. sp., a new ichthyopterygian (Reptilia) from the Early Triassic of Thailand. Comptes Rendus de l'Académie des Sciences. Série II, 313:1207–1212.Google Scholar
McGowan, C. 1972. The distinction between latipinnate and longipinnate ichthyosaurs. Life Science Occasional Papers, Royal Ontario Museum, 20:1–8.Google Scholar
McGowan, C. 1974a. A revision of the longipinnate ichthyosaurs of the Lower Jurassic of England, with descriptions of two new species (Reptilia: Ichthyosauria). Life Science Contribution, Royal Ontario Museum, 97:1–37.Google Scholar
McGowan, C. 1974b. A revision of the latipinnate ichthyosaurs of the Lower Jurassic of England (Reptilia: Ichthyosauria). Life Science Contributions, Royal Ontario Museum, 100:1–30.Google Scholar
McGowan, C. 1979. A revision of the Lower Jurassic ichthyosaurs of Germany with descriptions of two new species. Palaeontographica A, 166:93–135.Google Scholar
Motani, R. In press. New information on the forefin of Utatsusaurus hataii (Ichthyosauria). Journal of Paleontology.Google Scholar
Motani, R., You, H., and McGowan, C. 1996. Eel-like swimming in the earliest ichthyosaurs. Nature, 382:347–348.Google Scholar
Nicholls, E. L., and Brinkman, D. B. 1995. A new ichthyosaur from the Triassic of Sulphur Mountain Formation of British Columbia, p. 521–535. In Sarjeant, W. A. S. (ed.), Vertebrate Fossils and the Evolution of Scientific Concepts. Gordon and Breach Publishers, London.Google Scholar
Rieppel, O. 1992a. Studies on skeleton formation in reptiles. I. The postembrionic development of the skeleton in Cyrtodactylus pubisulcus (Reptilia, Gekkonidae). Journal of Zoology. London, 227:87–100.Google Scholar
Rieppel, O. 1992b. Studies on skeleton formation in reptiles. III. Patterns of ossification in the skeleton of Lacerta vivipara Jacquin (Reptilia, Squamata). Fieldiana Zoology, Ne. Series, 68:1–25.Google Scholar
Rieppel, O. 1992c. The skeleton of a juvenile Lanthanotus (Varanoidea). Amphibia-Reptilia, 13:27–34.Google Scholar
Rieppel, O. 1993. Studies on skeleton formation in reptiles. II. Chameleo hoehnelii (Squamata: Chamaeleoninae), with comments on the homology of carpal and tarsal bones. Herpetologica, 49:66–78.Google Scholar
Shikama, T., Kamei, T., and Murata, M. 1978. Early Triassic Ichthyosaurus, Utatsusaurus hataii gen. et sp. nov., from the Kitakami Massif, Northeast Japan. Science Reports of the Tohoku University, Sendai. Second Series (Geology), 48:77–97.Google Scholar
Shubin, N. H., and Alberch, P. 1986. A morphogenetic approach to the origin and basic organization of the tetrapod limb. pp. 319–387. In Hecht, M. K., Wallace, B., and Prance, G. T. (eds.), Evolutionary Biology, Volume 20. Plenum Press, New York and London.Google Scholar
Wiman, C. 1933. Über Grippia longirostris . Nova Acta Regiae Societatis Scientiarum Upsaliensis, 9(4):1–19.Google Scholar