Spinosaurids (Diapsida: Spinosauridae) and sphenacodontids (Synapsida:
Sphenacodontidae) share not only a characteristic tall neural spines, but also
an atypical – compared to their close respective relatives – ecology, i.e.
apparently piscivorous and possibly semiaquatic mode of life. This similarity
might hold clue for the role of their sails. It is here suggested that sails of
these animals 1) served thermoregulatory function, warming the animals, otherwise
submerged in the water, as well as 2) enabled them to hunt for fish in a way
similar to the technique of Recent diapsid, black heron (Egretta ardesiaca).
Hervé Bocherens, Martin Cotte, Ricardo A. Bonini, Pablo Straccia, Daniel Scian, Leopoldo Soibelzon, Francisco J. Prevosti (2017)
Isotopic insight on paleodiet of extinct Pleistocene megafaunal Xenarthrans from Argentina.
Gondwana Research (advance online publication)
Carbon isotope spacing between collagen and carbonate in fossil bone revealed the diet of extinct giant Xenarthrans.
Fossil bones from the Pampean region were well preserved for collagen and carbonate.
Spacing carbon isotope values indicate herbivorous diet for Glyptodontids and giant ground sloths.
No evidence of insectivory or carnivory for Megatherium
The diet of extinct giant Xenarthrans is a debated topic, especially for ground sloths, for which herbivory, insectivory, and carnivory through scavenging or active hunting have been suggested. In this study, stable carbon isotopic composition of collagen and carbonate fraction of well-preserved fossil bones was used as a tracer of trophic level. > 200 modern mammal bones of species with a variety of diets were used as a reference dataset. The good preservation of the carbonate isotopic composition was checked using different diagenetic indicators and by using fossil carnivorous and herbivorous taxa from the same sites as test-taxa. The results on modern mammals indicate a clear distinction in the difference between the carbon isotopic composition of carbonate and collagen between faunivores (carnivores, insectivores, piscivores, omnivores) and herbivores. Using this framework, the results on the fossil megafaunal Xenarthrans indicate a herbivorous diet for both Glyptodontids and are also consistent with a herbivorous diet for giant ground sloths, including Megatherium. The hypothesis that Megatherium could be a cryptic meat-eater or an insectivore is not supported by the results obtained in the present study.