Large animals have larger bones to support their massive bodies, but smaller species can also possess incredibly strong skeletons.
The largest skeleton of a living animal today belongs to the blue whale (Balaenoptera musculus), but its bones are neither the densest nor the strongest. Bones with lower density provide greater buoyancy, aiding these creatures in easily surfacing for air after deep dives.
Rhinoceros has incredibly strong thigh bones. (Photo: Peter van Dam).
However, the situation for land animals is different. Lacking the support of water, these giants must undergo significant structural changes in their bones to grow to larger sizes. One of the largest land animals in history is Patagotitan mayorum, an extinct dinosaur. With an estimated length of 37 meters and weighing around 70 tons, their bones need to be exceptionally strong to support their bodies.
In the animal kingdom, thigh bones are often incredibly strong, but which animal has the strongest?
A potential candidate is the rhinoceros. Evolutionary biologist Ben Garrod, a professor at the University of East Anglia, explains in the BBC documentary series Secrets of Bones that: “the thigh bone of a rhinoceros can withstand a compressive force of 109 tons.” He reached this conclusion by inferring data from the European roe deer (Capreolus capreolus). The European roe deer averages only 75 cm in height and weighs 25 kg. However, tests at the University of Bath show that their slender thigh bones can withstand up to 1.7 tons of compressive force before breaking.
Hero shrew (left) and its spine (right). (Photo: Julian Kerbis Peterhans/John Weinstein/Field Museum)
Other formidable candidates include the Thor hero shrew (Scutisorex thori) and hero shrew (Scutisorex somereni) found in the forests of Central Africa. Despite their small size, their spines are remarkably unique.
The spine serves a critical role in supporting the head, protecting the spinal cord, and safeguarding the important blood vessels that connect to and from the brain. Spines are notoriously difficult to break. Neurosurgeon Marc Otten estimates that it takes a force greater than 3,000 newtons to break a cervical vertebra. However, this strength is still no match for the spines of the two aforementioned small shrew species.
The Thor hero shrew and the hero shrew are rare mammals known to possess interlocking vertebrae. The differences become stark when comparing their spines to the white-toothed shrew (Crocidurinae).
Spine of the white-toothed shrew (top) and spine of the hero shrew (bottom). Photo: J.A. Allen/Herbet Lang/James Paul Chapin
In a study published in the journal Proceedings of the Royal Society B in 2020, expert Stephanie Smith at the Field Museum of Natural History and colleagues analyzed the 3D structure of their bones. The results revealed remarkably tightly packed and dense vertebrae. Their spines also feature several reinforcing structures that enhance strength.
The strength of the hero shrew is said to have astonished American and European explorers in the 1910s when the indigenous Mangbetu people of Congo demonstrated that an adult man could step on them without injury. Scientists are unclear about the exact reasons these shrews developed such unique spines, but one hypothesis suggests that strong spines allow them to twist and contort their bodies to tear wood while foraging.
