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Reproductive Behaviour
Abstract
According to both ethological and physiological criteria, the reproductive behaviour of the majority of vertebrates has two phases, a sexual phase and a phase of parental care (Blüm 1986). The objective of the sexual phase in chelonians is copulation and the insemination of the female. Parental care is mostly limited to nesting, the concealment of the eggs in a favourable place, which is solely the task of the female. Only a few chelonian species show nest guarding behaviour.
... Extant turtles prefer sandy sediments, when available, to lay their eggs (Kuchling, 1999), and all extant marine turtles dig their nest in sandy supratidal areas (Hendrickson and Balasingam, 1966;Stancyk and Ross, 1978;Bonach et al., 2011), resorting to clay or silt substrates only when sand is scarce. Even in these cases, nesting in muddy substrates results in high mortality rates, due to the differences in humidity and temperature exchange in these nests (Mortimer, 1990;Marco et al., 2017). ...
... Even in these cases, nesting in muddy substrates results in high mortality rates, due to the differences in humidity and temperature exchange in these nests (Mortimer, 1990;Marco et al., 2017). If sand bars are not available in their habitat, turtles (e.g., the cryptodiran Batagur baska) are known to travel several tens of kilometres up freshwater streams in order to find adequate nesting substrates (Pritchard, 1979;Kuchling, 1999). ...
... Turtles prefer sandy sediments for nest building (Kuchling, 1999). Muddy deposits dominate the littoral area of the Sobrarbe Deltaic Complex, as evidenced by the large amount of marls and siltites in the CS-41 section. ...
The Eocene record of turtle eggshells is scarce, with a single unconfirmed report from France. This scarcity contrasts with the great abundance of osteological remains, distributed over a wide palaeogeographical range as a result of climatic warmth. In this paper, we describe the first definitive Eocene Testudoolithidae eggshell fragments attributable to Testudines, most likely pleurodiran turtles, from the Eocene Sobrarbe Formation at the Castejón de Sobrarbe fossil site (CS-41) in northern Spain. The eggshells were found in association with osteological remains of at least four individuals of Eocenochelus eremberti (Pleurodira, Erymnochelyini) in an otherwise sirenian-dominated bonebed. Analysis of eggshell ultra- and microstructure allows comparison with eggshells from fossil and extant turtles. The eggshells are highly recrystallized but preserve relics of their original aragonitic radial ultrastructure as crystal phantoms. The barrel-shaped shell units, which are taller than wide, with compactituberculate ornamentation and funnel-shaped pore openings are similar to those of the Palaeocene ootaxon Haininchelys curiosa, whose holotype and paratype have been lost. The CS-41 eggshells are most similar to those of the pleurodiran Erymnochelys madagascariensis from Madagascar, the closest living relative to Eocenochelus, further supporting our attribution. Sedimentological and taphonomic analysis of the assemblage supports the hypothesis that the CS-41 fossil site was formed as the infilling of an abandoned tributary channel in the deltaic plain by an overbank or debris-flow deposit associated with a storm event. This storm reworked the remains of a nesting ground of Eocenochelus eremberti, an otherwise coastal turtle, which would have entered inland streams to nest in the sand bars at the mouth of the Sobrarbe Deltaic Complex.
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