Defence and signalling

Helmet or headdress?

For years we thought dinosaurs only used their head adornments for defence against predators. However, the growing evidence from fossils and modern animal behaviour has revealed they were used for much more than that.

How do living animals use their horns and headgear?

Horns for competition

• Many male animals use horns to fight for mating rights and social positions, and as display features to attract females. Horns also have a role in defence.
• Wounds on some ceratopsian skulls appear to have been inflicted by a member of the same species. This supports the possibility that they competed with each other.

Headgear for bluff

• Some animals try to look threatening when confronted by danger.
• Most ceratopsians have openings in their bony frills that may have made them unsuitable for defence. Their frills may have instead had coloured markings to bluff predators.

Horns for defence

• Rhinos use horns in offensive and defensive charges, to shovel for food and fight other rhinos for territory and mating rights.
• Studies on the strengths of ceratopsian frills and horns indicate they would not have withstood the impact of a full-frontal charge at a predator.

Crests for sound

• Cassowary crests may be sensory devices to receive sound signals. The horn of the Wrinkled Hornbill is used primarily as a resonating chamber to amplify calls.
• Some hadrosaurs had hollow head crests that could have made sounds when air was forced through them

Armour or amour?

Stegosaurs and ankylosaurs were built for defence. The ankylosaurs took it to the extreme, with thickened skulls, fused vertebrae and compact bodies earning them the nickname ‘nature’s tanks’. Interestingly, there is no evidence that either group lived in herds so reliance on self-defence makes sense. However, nothing is quite as simple as it seems. Some of these features may also have been used for mating displays, regulating body temperatures, or to help recognise others of their species.

Stegosaurs

Stegosaurs are known for the rows of plates and spikes on their backs and tails (which differed between species). Evidence suggests the plates contained networks of blood vessels that could have been for regulating body temperature. Skin over the plates could have been coloured for display or to help differentiate between species or bluff predators.

Examples of stegosaurs include:

• Kentrosaurus aethiopicus – Tanzania, 156–146million years ago
• Huayangosaurus taibaii – China, 161–156 million years ago
• Wuerhosaurus homheni – China, 151–100 million years ago

Did you know?

The group of spikes on the tails of stegosaurs now has an official scientific name – the thagomizer. The term was chosen to honour Gary Larson and his many years of off-beat dinosaur humour. He first used the word in a Far Side cartoon when describing the spiked tail that caused the death of caveman Thag Simmons.

Ankylosaurs

There were three types of ankylosaurs – the nodosaurids, ankylosaurids and polacanthids. They differed slightly in a number of features including the shape of the skull, structure of the tail, and amount and structure of boney body spines and armour.

Examples of ankylosaurs include:

• Sauropelta edwardsorum – nodosaurid, North America, 108 million years ago
• Euoplocephalus tutus – ankylosaurid, North America, 76–75 million years ago
• Gargoyleosaurus parkpini – polacanthid, North America, 154–150 million years ago

Run and hide

The lives of most small plant-eating dinosaurs depended on an ability to flee danger or avoid being spotted. The best exponents of the ‘run and hide’ tactic were hypsilophodontids, often described as the ‘gazelles’ of the dinosaur world. They would have been continually alert, with lightweight bodies and long legs built for speed. It is also likely that they used camouflage to blend in to their surroundings, just like many animals today.