Abstract

Parental care is found in all extant archosaurs (crocodylians and birds) and parsimony suggests this behavior is homologous. There are known ‘parent atop eggs’ fossils of nonavian theropod dinosaurs (ancestors to birds), but no equivalent fossil for crocodylians has been reported yet within this context. Here we present a remarkable fossil of an adult crocodylian (Diplocynodon darwini) preserved in situ with eggs from the middle Eocene of Geiseltal, Germany, providing the first-reported evidence for the antiquity of parental care in the crocodylian lineage. The degree of articulation, the unusual curled posture of the adult, the position of the eggs, and the surrounding sediment indicate the adult may have died atop its nest after oviposition. Size relationships between the adult and eggs are consistent with values from modern related taxa and no other crocodylian was found within 12 m of the eggs. Thorough documentation of fossil vertebrate skeletons collected near the fossil crocodylian does not indicate flow influenced its curled posture. Despite being sexually mature, the adult crocodylian did not exhibit full fusion of the neurocentral sutures, an indicator of immaturity in nonavian archosaurs. Even in a paratropic environment, temperatures may temporarily drop below cold tolerance for warm-adapted crocodylians, possibly explaining the death of the adult and the young inside the eggs. Although still indicating egg attendance, the fossil may alternatively indicate the mother died from dystocia (egg-binding) during oviposition, which would be to our knowledge the first published record of this rare phenomenon in a fossil archosaur.

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