The horned and plated dinosaurs evolved some of the most spectacular features ever seen on land. They had giant frills around their necks, triangular plates running along their backs, sharp horns above their eyes, and spikes around their heads. At first glance, these all look like weapons - and some were. But modern research suggests many of these features were primarily for display: signalling to rivals, attracting mates, or showing off their species, much like a peacock's tail. Pentaceratops, shown here, had the largest skull of any land animal ever known, including a frill that stretched up to 3 metres (10 feet) from snout to crest. A male's huge frill may have been used to impress females as much as to intimidate enemies.
Styracosaurus - the name itself means "spiked lizard." This Late Cretaceous horned dinosaur from Alberta, Canada, had a broad neck frill ringed at the top with six long, gently curved spikes, each up to 60 cm (2 feet) long. Smaller bony studs (called epoccipitals) ran along the rest of the frill's edge. Styracosaurus also had a single 60 cm horn on its nose, but no horns above the eyes - the opposite of Triceratops. The spikes were certainly intimidating, but were probably used mostly for showing off and for sparring with rivals of the same species, not for fighting off predators.
Styracosaurus skull
Yes - Triceratops ("three-horned face") had a 2-metre skull with a short nose horn and two longer brow horns up to 1 metre long each. Its frill was edged with bony studs and probably covered in skin. About 50 Triceratops skulls have been studied closely, and many show puncture wounds, scratches, and even broken horns that match the size and shape of Triceratops horns from rival individuals - clear evidence that they fought each other head-to-head, locking horns and shoving like modern deer or elk. Triceratops horns have also been found embedded in T. rex bite marks, proving they were used in defence against predators as well.
Triceratops skull
Yes, and the evidence is right there in their skulls. Many Late Cretaceous horned dinosaur skulls show scrapes, punctures, and healed injuries in exactly the spots where rival horns would have struck during a head-to-head shoving match. Just like modern stags during the rut, male horned dinosaurs probably fought each other for territory and mates. Some battles ended badly - several fossils show fatal punctures through the bone of the frill. The Styracosaurus shown here might be in such a confrontation. Importantly, these fights would usually have been ritualized contests rather than fights to the death - most disputes were probably settled with displays.
Styracosauruses
Stegosaurus's famous diamond-shaped back plates were almost certainly not defensive weapons. They were thin, not connected directly to the spine, and covered in skin laced with blood vessels - making them too fragile to protect against a bite. Scientists have proposed three main uses: temperature control (radiating heat in or out, like a radiator), display (showing off to mates or rivals), and species recognition (helping Stegosaurus identify members of its own species). The current consensus is mostly display, but recent research suggests the plates may also have flushed bright pink with blood when the dinosaur was excited or threatened - a stunning visual signal.
Stegosaurus
Spinosaurus, the giant fish-eating theropod from Cretaceous North Africa, had elongated vertebrae rising up to 2 metres (6.5 feet) above its back - taller than a person. Connected by skin, this formed a huge sail or ridge along the spine. The sail's exact purpose is still debated. It may have helped Spinosaurus shed heat in the hot African climate. It may have been used for display - to attract mates or scare rivals. It may even have helped the dinosaur move more efficiently through water, where recent research suggests Spinosaurus spent much of its time. Other dinosaurs like Ouranosaurus also had back sails, suggesting the structure evolved more than once.
Spinosaurus