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SCRAMBLED EGGS: SYNCHROTRON SCANS OF EGGS FROM THE EARLIEST JURASSIC SEEM TO
REVEAL UNUSUAL TRAITS IN EARLY DINOSAUR EMBRYOS

Using synchrotron propagation phase-contrast
microtomography on the BM05 beamline of the ESRF-EBS,
we analyzed the contents of four Hettangian eggs from a
dinosaur nesting site in Poland. The scans revealed that all
four eggs, which were collected from the same nest structure,
contain embryonic remains. The preservation of the bones
indicates a complex taphonomical history involving both
abiotic and biotic factors (e.g. invertebrate scavenging). The
embryos are highly disarticulated, and most bones are broken,
shattered, or missing. However, other bones are well
preserved, and scales, skin impressions and mineralized soft
tissues are present in some eggs. The incompleteness of the
skeletons makes identification of the embryos difficult, but a
theropod affinity of the embryos is suggested based on
eggshell microstructure, the presence of blade-like serrated
teeth, and a few cranial and postcranial skeletal features. The
embryos died at a late developmental stage, which is indicated
by ossification of cranial elements, fusion of the centrum with
the neural arch in distal caudal vertebrae, and by the eruption
of teeth. Interestingly, the embryos possessed osteoderm-like
epidermal structures, which is highly unusual for theropods,
and a palatal dentition, which contrasts with the condition seen
in most archosaurs. We postulate that palatal dentition might
have been a more widespread trait among juvenile dinosaurs
than previously known, and retention of palatal teeth in other
saurischian genera is likely the result of paedomorphism. The
analysis of dinosaur embryos using propagation phasecontract
microtomography enables the extraction of valuable
data even on highly disarticulated and incomplete embryonic
material, here exemplified by the study of the oldest probable
theropod embryos to date.