In situ analysis of vascular structures in fractured Tyrannosaurus rex rib.

Soft tissue preservation in fossils has become a popular focus of paleontology research due to easier access to sensitive probes like synchrotron radiation, allowing more detailed analysis of specimens. Although uncommon, reports exist on vascular preservation in dinosaurs, generally as remnants of Haversian canals. However, combined 3D morphological and chemical analysis of large angiogenic dinosaur blood vessels has not been reported before. Here we show characterization of a network of large vessel-like structures in a rib from "RSKM P2523.8" (Royal Saskatchewan Museum), an exceptionally robust Tyrannosaurus rex found in the Late Cretaceous Frenchman Formation, Saskatchewan, Canada. Using Synchrotron Micro-Computed Tomography these structures can be visualized in situ within the bone and matched to chemical microprobing from Synchrotron X-ray Fluorescence and X-ray Absorption Near Edge Structure. Combined with conventional optical and electron microscopy, we show the vessel-like structures are composed of pyrite partially oxidized to goethite or hematite, preserved in two distinct layers as permineralized casts. Although no original soft tissues were able to be recovered using the current suite of techniques, the structures' morphology and sole presence in a fractured area of the rib suggest angiogenic origin. Bone healing and regrowth may offer a promising target for future multi-technique soft tissue experiments analyzing dinosaur healing potential.