Abstract
A Late Cretaceous-aged multi-taxon nesting site from Romania preserved in three dimensions reveals the earliest example of nest site sharing yet known from the vertebrate fossil record. Eggshell and osteological evidence combined in this single accumulation demonstrate that at least four vertebrate taxa including enantiornithine birds and another avian of indeterminate affinities as well as crocodylomorphs and gekkotan squamates nested together in the same place. Colonial nesting in enantiornithines was previously described from this site; here, we present the first fossil evidence that other vertebrates also nested in the same place, perhaps exploiting the presence of the large bird colony. We describe four distinct eggshell morphotypes that have been collected from this site and draw palaeoecological inferences based on this unique multi-taxon nesting association.
Highlights
The eggs, hatchlings, nests, and nesting sites of extinct animals are relatively common in the vertebrate fossil record
Together with prismatic transitions, have been described from Mongolian Cretaceous bird eggs[45], and this has been cited as evidence for closer affinities with modern avians as opposed to basal ornithothoracines[45], while the known Bajo de la Carpa eggs have been associated with Ornithothoracines on the basis of embryonic evidence from this Neognathous morphotype[15,44,46] (Table 1)
These Romanian eggs can be assigned to enantiornithines, a conclusion which is further supported by their shell characteristics: two-layered ornithoid-basic type eggshell with subdivision of the second layer (CL) into to ultrastructural zones (SqZ and external zone (EZ)) and the presence of bird bones within the assemblage (Table 1)
Summary
The eggs, hatchlings, nests, and nesting sites of extinct animals are relatively common in the vertebrate fossil record. As far as it is known, both non-avialan theropod dinosaurs and Mesozoic birds had precocial young[2,10,13,14,15,21,22,23,24,25,26,27]; this contrasts with the altricial[3,28,29,30,31] young of many living Aves where energetically demanding parental care is required These behaviours include, but are not limited to, egg brooding and egg turning, both critical to improve hatching rate[32], hatchling feeding, and the construction of complex nests[10,33]. Sedimentological and taphonomic evidence[35] supports the conclusion that these additional vertebrate taxa were nesting within the same areas as the breeding enantiornithine colony, which makes the Od assemblage unique in the vertebrate fossil record
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