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Drowned Mesozoic enantiornithine bird breeding colony

From: Ben Creisler

A new online paper:

Gareth Dyke, Mátyás Vremir, Gary Kaiser and Darren Naish (2012)
A drowned Mesozoic bird breeding colony from the Late Cretaceous of
Transylvania .
Naturwissenschaften (advance online publication)
DOI: 10.1007/s00114-012-0917-1

Despite a rapidly improving fossil record, the reproductive biology of
Mesozoic birds remains poorly known: only a handful of undisputed,
isolated Cretaceous eggs (some containing embryonic remains) are
known. We report here the first fossil evidence for a breeding colony
of Mesozoic birds, preserved at the Late Cretaceous (Maastrichtian)
Oarda de Jos (Od) site in the Sebeş area of Transylvania, Romania. A
lens of calcareous mudstone with minimum dimensions of 80 cm length,
50 cm width and 20 cm depth contains thousands of tightly packed,
morphologically homogenous eggshell fragments, seven near-complete
eggs and neonatal and adult avialan skeletal elements. Eggshell forms
70–80 % of the matrix, and other fossils are entirely absent. The
bones exhibit clear characters of the Cretaceous avialan clade
Enantiornithes, and the eggshell morphology is also consistent with
this identification. Both taphonomy and lithology show that the
components of this lens were deposited in a single flood event, and we
conclude that it represents the drowned remains of a larger
enantiornithine breeding colony, swamped by rising water, washed a
short distance and deposited in a shallow, low-energy pond. The same
fate often befalls modern bird colonies. Such a large concentration of
breeding birds suggests aquatic feeding in this species, augments our
understanding of enantiornithine biology and shows that colonial
nesting was not unique to crown birds.