Adult sharks and rays have blood vessels growing through their cartilage, breaking a fundamental rule of biology.
April 25, 2026
Original Paper
Cartilage canals in sharks and rays show that blood vessels can exist in mature cartilage without triggering endochondral bone formation
bioRxiv · 10.64898/2026.04.21.720020
The Takeaway
Textbooks teach that healthy adult cartilage has no blood supply and that any vessel invasion will inevitably turn that cartilage into bone. Sharks and rays prove this wrong by maintaining complex networks of blood vessels inside their mature cartilage for their entire lives. This unique anatomy allows them to maintain a flexible skeleton that never ossifies despite having a direct blood connection. Understanding how they prevent this transition could lead to new treatments for human joint diseases and bone spurs. It shows that the biological trigger for bone growth is not as simple as we once thought. Flexibility and blood supply are not mutually exclusive in these ancient fish.
From the abstract
Although cartilage in tetrapod skeletons is typically said to lack blood vessels, this is only true for adult cartilage. In young bird and mammal cartilage, a dense network of vasculature-containing tunnels --cartilage canals-- perforate the growing skeleton, helping nourish the cartilage and develop the ossification centers that will later form the skeleton's epiphyseal bone. As the canals and their rich vascular network typically recede as animals age, the healthy cartilage of adult animals is