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Unique in situ dinosaur clutch with an outsiders egg
Institución organizadora:
Zhejiang Museum of Natural History
Northern Patagonian outcrops contain a number of excellent localities where Upper Cretaceous rocks are well exposed. Among these, the Allen Formation is dated as middle Campanian- early Maastrichtian in age, based on foraminifera presence (Ballent, 1980) and it is composed by a thick succession of sandstones and mudstones intercalated by carbonate and evaporitic rocks in its upper part (Salgado et al., 2007). In 2008, two clutches, ?a? containing 4 Faveoloolithid eggs and clutch ?b? containing 10 eggs, 9 of them are Faveoloolithid eggs while 1 of them is a Dendroolithid egg, the clutches were found in the egg-level 4 at the Bajos de Santa Rosa locality (Salgado et al., 2007; Fernández 2013). A second place with few Faveoloolithid eggs and just few Dendroolithid eggshells were found 200 mts in the south from Berthe VI site, in egg level 4. Eggs and eggshells were studied with SEM, and several thin sections were investigated under PLM. Geology and taphonomy was studied with X-ray analysis to characterize the sediments and morphological traits were recognized in the field. Clutches were mapped with a 1 x 1 mts grid. Three possible hypotheses were studied to explain this phenomenon. The first one consists in a pedogenic process, which include the influence of vertisol development on a dinosaur nest taphonomy. This process might have occasioned that a foreign eggs roll into the nest. This hypothesis was discarded for the evidence of the paleosoils, the clutches were found in situ, and there is no evidence of vertisol soils in this area. The second hypothesis involves a type of brood parasitism behavior. This reproductive strategy is widespread in modern birds. The first female laid its eggs in a clutch, and later a second female lays just one egg in the previous nest, like Cuculus canorus do. The characteristic of this behaviour consist on that the foraging hatchling will destroyed the eggs of the first female, who will take care of foraging hatchling, taking advantages of their parental care. We could not verify that the outsider hatchling hurt the original eggs of the clutch. Finally, the third hypothesis involve a communal nesting breeding, it is well known in the field that some lizard like Salvator merianae use to laid their eggs into the nest of Caiman latirostris (personal communication Dra. Melina Simoncini 2016), in the other hand some South American gecko Homonota darwinii often laid their eggs alongside nesting gulls (Larus spp.), cormorants (Phalacrocorax spp.) and these geckos use nesting areas for shelter, warmth and the opportunity to feed on the algae that the birds use to construct the nest (Personal communication Alejandro Scolaro 2016). The Lesser rhea (Pterocnemia pennata) and Elegant crested tinamou (Eudromia elegans) often nest and brood alongside penguins in Patagonia with total interspecific tolerance (Scolaro 1985). Based on these extant examples, it is parsimonious to expect similar behaviours in the past.