A new study published in Nature reveals that Spinosaurus, among the largest carnivorous dinosaurs ever discovered, could hunt underwater.
New research by a multi-institution team including the Field Museum of Natural History, Chicago, the University of Oxford and the University of Cambridge used X-ray imaging of fossilised bones to analyse bone density. By comparing the bone structure of living animals and birds that forage in the water, researchers found strong evidence that dinosaurs from the spinosaurid family swam underwater to search for prey.
Spinosaurid dinosaurs look like T. rex, but with a long, narrow snout and short legs. They include species like Spinosaurus from northern Africa, and Baryonyx from England, and were first discovered in 1915. Spinosaurus was similar in size to T. rex, weighing up to 7 tonnes, with a large crest-like sail across its back.
Fossilised gut contents show that spinosaurids were amphibious hunters - eating both surf and turf - but it has been debated whether they caught fish in the water like a crocodile or hunted from the shallows like a heron.
Some palaeontologists have suggested that spinosaurids were specialist aquatic predators, based on their long snout, and a tail fin that might have been used for propulsion in water, as well as other evidence. However, fossil footprints show that most dinosaurs walked on land, and evidence for swimming is rare.
The new study used data on skeletal bone density to resolve whether spinosaurids swam underwater. Using CT scanning (a form of 3D x-ray imaging) the researchers collected femur and rib bone cross-sections from more than 200 living animals, including those that hunt in the water like otters and those that forage on land like badgers. The researchers compared these cross-sections to those of many dinosaurs, including three spinosaurids: Spinosaurus, Baryonyx and Suchomimus.
The scans showed that animals that submerge themselves underwater to find food have bones that are almost completely solid throughout, whereas cross-sections of land-dwellers' bones look more like doughnuts, with hollow centres.
