76 - 3D Histology of bone vasculature and life history in juvenile tyrannosaurs compared to modern ratites

Poster Board Number: 76
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Co-authors:

Eric Snively - Associate Professor of Anatomy, Biomedical Sciences, Oklahoma State University College of Osteopathic Medicine; Holly Woodward - Professor of Anatomy and Paleontology, Biomedical Sciences, Oklahoma State University Center for Health Sciences

Abstract Body : Introduction. Osteohistology of extant taxa is commonly compared to that of extinct vertebrates to interpret biology of extinct clades. Recently, non-consumptive microCT scans have supplemented traditional thin sectioning. Although not as detailed at the tissue and cellular level, these 3D scans allow for better interpretation and reconstruction of complicated vasculature. Therefore, the objective of this study is a detailed examination of 3D vasculature networks in skeletally immature tyrannosaurs and extant ratites to investigate remodeling through growth, maturity, and locomotor loading.

Methods. Synchrotron phase contrast microCT improves edge definition and resolution with larger specimens. At the Canadian Light Source Synchrotron MBIT beamline, we scanned metatarsals and femora of juvenile tyrannosaurids from yearling to teenage status, and hindlimb elements of ratites for extant grounding of interpretations. Attenuation-based microCT was also performed to compare tissue densities. AVIZO software reconstructed the scans into 3D models.

Results. 3D imaging revealed abundant oblique canals, a vasculature type often mistakenly interpreted and underreported in 2D thin sections. These canals can sometimes be indistinguishable from longitudinal canals in 2D but are readily apparent in 3D. They represent fast growth and/or increased nutrient transport to tendon and ligament attachments. Cortical canal densities correlate inversely with maturity in both the ratites and tyrannosaurids. Mineralized endosteal tissue is also apparent in a single teenage tyrannosaur, closely resembling medullary tissue in an adult kiwi, which could mark the onset of reproductive maturity and act as a rare marker for sex identification in avian dinosaurs.

Conclusion. Results demonstrate synergy between planar but higher-resolving 2D histology and volumetric sampling possible with synchrotron micro-CT. 3D vascular structure confirmed interpretations of predominant canal direction and remodeling zones identified from ground thin sections. Younger tyrannosaurs and ratites exhibit dense vascularization, with more ordered vascular patterning appearing in the youngest Gorgosaurus and emu specimens. The older tyrannosaur was probably experiencing resorptive remodeling from reproductive changes.

These findings reveal greater growth plasticity in tyrannosaurs than in ratites. Through characterizing 3D vasculature with age, 3D histological modelling has the potential to circumscribe fossil specimen ages based on vasculature densities. Prospective medullary bone in a teenage tyrannosaur promises potential identification of sex and age of sexual maturity in such individuals.