Scientists have long debated the biogenic origin of secondary eggshell units (SEUs) in dinosaur eggs. A new study has finally shed light on this mystery, confirming that these structures are indeed biogenic.
Researchers from the Institute of Vertebrate Paleontology and Paleoanthropology led by Dr. Zhang Shukang and Dr. Choi Seung have conducted a comprehensive study on SEUs using advanced techniques such as electron backscatter diffraction, polarized light microscopy, and scanning electron microscopy.
Their findings suggest that the crystallographic characteristics of dinosaur egg SEUs are almost identical to those of primary eggshell units (PEUs), which are found in modern birds. Notably, they also matched the crystallographic characteristics of SEUs in modern turtle and crocodile eggshells.
The researchers discovered that the SEUs exhibited numerous grooves and vesicles, similar to those in modern bird eggshell units, which were likely remnants of spaces left by the degradation of organic matrix fibers during fossilization. This suggests that the SEUs are biogenic structures.
Moreover, the study found that in some dinosaur eggshells with well-developed pore canals, the SEUs either overlapped the PEUs or grew inside the pore canals, challenging the “competition hypothesis” derived from modern bird eggshells.
The researchers also discovered that the formation mechanism of SEUs may have changed during the evolution of eggshells from non-avian theropods to modern birds. The presence of SEUs in various dinosaur lineages, including turtles and crocodilians, suggests that these structures may have evolved independently within the calcitic layers of eggshells.
This study provides new insights into the evolutionary plasticity of eggshell structures and sheds light on the characterization of SEUs in dinosaur eggshells.
Source: https://phys.org/news/2025-05-dinosaur-eggshell-biogenic-secondary.html