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Naturwissenschaften

, Volume 95, Issue 1, pp 79–84 | Cite as

Salt glands in the Jurassic metriorhynchid Geosaurus: implications for the evolution of osmoregulation in Mesozoic marine crocodyliforms

  • Marta Fernández
  • Zulma Gasparini
Short Communication

Abstract

The presence of salt-excreting glands in extinct marine sauropsids has been long suspected based on skull morphology. Previously, we described for the first time the natural casts of salt-excreting glands in the head of the Jurassic metriorhynchid crocodyliform Geosaurus araucanensis from the Tithonian of the Vaca Muerta Formation in the Neuquén Basin (Argentina). In the present study, salt-excreting glands are identified in three new individuals (adult, a sub-adult and a juvenile) referable to the same species. New material provides significant information on the salt glands form and function and permit integration of evolutionary scenarios proposed on a physiological basis in extant taxa with evidence from the fossil record. G. araucanensis represents an advanced stage of the basic physiological model to marine adaptations in reptiles. G. araucanensis salt glands were hypertrophied. On this basis, it can be hypothesized that these glands had a high excretory capability. This stage implies that G. araucanensis (like extant pelagic reptiles, e.g. cheloniids) could have maintained constant plasma osmolality even when seawater or osmoconforming prey were ingested. A gradual model of marine adaptation in crocodyliforms based on physiology (freshwater to coastal/estuarine to estuarine /marine to pelagic life) is congruent with the phylogeny of crocodyliforms based on skeletal morphology. The fossil record suggests that the stage of marine pelagic adaptation was achieved by the Early Middle Jurassic. Salt gland size in the juvenile suggests that juveniles were, like adults, pelagic.

Keywords

Geosaurus araucanensis Jurassic Salt gland 

Notes

Acknowledgements

We thank L. Witmer for suggestions on an early draft. The paper benefited from comments by D. Pol, C. McHenry and an anonymous reviewer. Financial support received from Agencia Nacional de Promociones Científicas y Tecnológicas de Argentina (PICT 25276), Consejo Nacional de Investigaciones Científicas y Tecnológicas de Argentina (PIP 5156/4) and Universidad Nacional de La Plata (N 463) is gratefully acknowledged.

References

  1. Dunson WA (1976) Salt glands in reptiles. In: Gans C (ed) Biology of the reptilia, vol 5. Academic, London, pp 413–445Google Scholar
  2. Dunson WA, Mazzotti FJ (1989) Salinity as a limiting factor in the distribution of reptiles in Florida bay: a theory for the estuarine origin of marine snakes and turtles. Bull Mar Sci 44:229–244Google Scholar
  3. Fernández M, Gasparini Z (2000) Salt glands in a Tithonian metriorhynchid crocodyliform and their physiological significance. Lethaia 33:269–276CrossRefGoogle Scholar
  4. Gandola R, Buffetaut E, Monaghan N, Dyke G (2006) Salt glands in the fossil Crocodile Metriorhynchus. J Vertebr Paleontol 26:1009–1010CrossRefGoogle Scholar
  5. Gasparini Z, Dellapé D (1976) Un nuevo cocodrilo marino (Thalattosuchia, Metriorhynchidae) de la Formación Vaca Muerta (Jurásico, Tithoniano) de la provincia del Neuquén. Act I Congr Geol Chileno Santiago 1:C1–C21Google Scholar
  6. Gasparini Z, Spalletti L, Fernández M, de la Fuente M (1999) Tithonian marine reptiles from the Neuquén basin: diversity and paleoenvironments. Revue Paléobiol 18:335–345Google Scholar
  7. Gasparini Z, Pol D, Spalletti L (2006) An unusual marine Crocodyliform from the Jurassic–Cretaceous boundary of Patagonia. Science 311:70–73PubMedCrossRefGoogle Scholar
  8. Jackson K, Butler DG, Brooks DR (1996) Habitat and phylogeny influence salinity discrimination in crocodilians: implications for osmoregulatory physiology and historical biogeography. Biol J Linn Soc 58:371–383CrossRefGoogle Scholar
  9. Hazard LC (2001) Ion secretion by salt glands of Desert Iguanas (Dipsosaurus dorsalis). Phys Biochem Zool 74:22–31CrossRefGoogle Scholar
  10. Hazard LC (2004) Sodium and potassium secretion by iguana salt glands: acclimation or adaptation? In: Alberts A, Carter RL, Hayes WB, Martins E (eds) Iguanas: biology and conservation. University of California Press, California, pp 84–93Google Scholar
  11. Hirayama R (1998) Oldest known sea turtle. Nature 92:705–708CrossRefGoogle Scholar
  12. Hopson JA (1979) Paleoneurology. In: Gans C, Northcutt RG, Ulinski P (eds) Biology of the Reptilia, vol 9. Academic, London, pp 39–146Google Scholar
  13. Hua S, de Buffrenil V (1996) Bone histology as a clue in the interpretation of functional adaptations in the Thalattosuchia (Reptilia, Crocodylia). J Vertebr Paleontol 16:703–717CrossRefGoogle Scholar
  14. Marples BJ (1932) The structure and development of the nasal glands of birds. Proc Zool Soc Lond 2:829–844Google Scholar
  15. Mazzotti FJ, Dunson WA (1989) Osmoregulation in Crocodilians. Am Zool 29:903–920Google Scholar
  16. Peaker M, Linzell JL (1975) Salt glands in birds and reptiles. Cambridge University Press, LondonGoogle Scholar
  17. Schmidt-Nielsen K, Fange R (1958) Salt glands in marine reptiles. Nature 4638:783–785CrossRefGoogle Scholar
  18. Staaland H (1967) Anatomical and physiological adaptations of the nasal glands of Charadriiformes birds. Comp Biochem Phys 23:933–944CrossRefGoogle Scholar
  19. Tapplin LE, Griggs GC (1981) Salt glands in the tongue of the Estuarine Crocodile, Crocodylus porosus. Science 212:1045–1047CrossRefGoogle Scholar
  20. Witmer LM (1995a) The extant phylogenetic bracket and the importance of reconstructing soft tissue in fossils. In: Thomason J (ed) Functional morphology in vertebrate paleontology. Cambridge University Press, Cambridge, pp 19–33Google Scholar
  21. Witmer LM (1995b) Homology of facial structures in extant archosaurs (birds and crocodilians), with special reference to paranasal pneumaticity and nasal conchae. J Morphol 225:269–327CrossRefGoogle Scholar
  22. Witmer LM (1997) The evolution of the antorbital cavity of Archosaurs: a study in soft- tissue reconstruction in the fossil record with an analysis of function of pneumaticity. Soc Vertebr Paleontol Mem 3:1–73Google Scholar

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Departamento Paleontología VertebradosMuseo de La PlataLa PlataArgentina

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