Defence and signalling
It sounds like a fancy dress party gone wrong: horns, dome-heads, crests, frills, noise, head-butting and rivalry. But they are really about using your head and some plant-eating dinosaurs excelled at it. And then there's armoured skin, body spikes, plates and clubbed tails – just try to sink your teeth into that! Or you can run and hide, using camouflage to blend in.
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 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 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, 156–151 million years ago
- Huayangosaurus taibaii – China, 168–161 million years ago
- Wuerhosaurus homheni – China, 140–100 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.
There were three types of ankylosaurs – the nodosaurids, ankylosaurids and polacanthids. They differed slightly in a number of features including shape of the skull, structure of the tail, and amount and structure of body spines and armour.
Examples of ankylosaurs include:
- Sauropelta edwardsorum – nodosaurid, USA, 115–112 million years ago
- Euoplocephalus tutus – ankylosaurid, North America, 76–68 million years ago
- Gargoyleosaurus parkpini – polacanthid, North America, 156–146 million years ago
Run and hide
What would you do if you lacked size or weapons to defend yourself from a large and hungry predator? The answer, hopefully, is pretty obvious. This was also the natural response for most small plant-eating dinosaurs, whose lives depended on an ability to flee danger or avoid being spotted. The best exponents of the ‘run and hide’ tactic were hypsilophodontians, 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.
Camouflage in living animals takes different forms. For example, Cunningham’s Skinks have skin colours that match their surroundings, while Zebras have stripes that blend with the herd, making them appear as one large entity.
Fran Dorey , Exhibition Project Coordinator