Paleobiological significance of hypertrophied salt-secreting glands in Geosaurus araucanensis (Crocodiliformes:Metriorynchidae)

FERNÁNDEZ, M. ; GASPARINI, Z.

Ottawa, Canada

Simposio; Marine Reptiles Symposium, 66th Annual Meeting Soc.Vertebrate Paleontology; 2006

Society of vertebrate Paleontology

The natural cast of salt-secreting glands, housed at the antorbital cavity of the skull, has been described in two adults of the Tithonian metriorhynchid Geosaurus araucanesis. This finding represented the first directed evidence of an extra-renal osmoregulatory system in extinct marine archosaurs. A new juvenile specimen of G. araucanesis bearing similar antorbital structures as the two adults described before, has been recently found. The large gland size, and the number and sizes of the lobules found in G. araucanensis suggest that these glands had high secretory capacity. According to the model of gradual evolutionary specialization of marine reptiles from a freshwater ancestor, this metriorhynchid represents the final stage. The final stage implies hypertrophied salt-secreting glands allowing the maintenance of a constant plasma osmolality even when sea water and osmoconforming preys are ingested. In extant reptiles this final stage is represented by sea turtles, marine iguana and sea snake, but not crocodiles. We proposed that the salt-secreting glands of Geosaurus araucanesis. This finding represented the first directed evidence of an extra-renal osmoregulatory system in extinct marine archosaurs. A new juvenile specimen of G. araucanesis bearing similar antorbital structures as the two adults described before, has been recently found. The large gland size, and the number and sizes of the lobules found in G. araucanensis suggest that these glands had high secretory capacity. According to the model of gradual evolutionary specialization of marine reptiles from a freshwater ancestor, this metriorhynchid represents the final stage. The final stage implies hypertrophied salt-secreting glands allowing the maintenance of a constant plasma osmolality even when sea water and osmoconforming preys are ingested. In extant reptiles this final stage is represented by sea turtles, marine iguana and sea snake, but not crocodiles. We proposed that the salt-secreting glands of G. araucanesis bearing similar antorbital structures as the two adults described before, has been recently found. The large gland size, and the number and sizes of the lobules found in G. araucanensis suggest that these glands had high secretory capacity. According to the model of gradual evolutionary specialization of marine reptiles from a freshwater ancestor, this metriorhynchid represents the final stage. The final stage implies hypertrophied salt-secreting glands allowing the maintenance of a constant plasma osmolality even when sea water and osmoconforming preys are ingested. In extant reptiles this final stage is represented by sea turtles, marine iguana and sea snake, but not crocodiles. We proposed that the salt-secreting glands of G. araucanensis suggest that these glands had high secretory capacity. According to the model of gradual evolutionary specialization of marine reptiles from a freshwater ancestor, this metriorhynchid represents the final stage. The final stage implies hypertrophied salt-secreting glands allowing the maintenance of a constant plasma osmolality even when sea water and osmoconforming preys are ingested. In extant reptiles this final stage is represented by sea turtles, marine iguana and sea snake, but not crocodiles. We proposed that the salt-secreting glands of Geosaurus drained through the antorbital fenestra and that the antorbital fossa housed at least a portion of its ducts. The development of salt-secreting glands of high sercretory capacity is also inferred in the other metriorhynchids Metriorhynchus and Dakosaurus. The size inferred of salt-secreting glands in the juvenile specimen, suggests that hatches had salt-secreting glands large enough to cope with the osmoregulatory demands of open sea life. drained through the antorbital fenestra and that the antorbital fossa housed at least a portion of its ducts. The development of salt-secreting glands of high sercretory capacity is also inferred in the other metriorhynchids Metriorhynchus and Dakosaurus. The size inferred of salt-secreting glands in the juvenile specimen, suggests that hatches had salt-secreting glands large enough to cope with the osmoregulatory demands of open sea life. Metriorhynchus and Dakosaurus. The size inferred of salt-secreting glands in the juvenile specimen, suggests that hatches had salt-secreting glands large enough to cope with the osmoregulatory demands of open sea life.