They are probably one of the most famous dinosaurs to be discovered due to the distinctive line of armoured plates along its back . Now new research revealed that male and female stegosaurus had different shaped plates running along their backs . It raises the prospect that the dinosaurs used its giant bony protrusions , which could reach up to 2.5 feet , to attract a mate . Scientists have found that male stegosaurus ( top ) had different shaped armoured plates to females ( bottom ) Palaeontologists say male stegosaurus could have used them to show off their prowess in much the same way as peacocks do today . The research has also helped to answer a problem that has baffled palaeontologists for decades . A pair of turkey-sized ‘ egg thief lizards ’ dubbed Romeo and Juliet were found lying next to each other in a 75-million-year-old rock in the mid-90s , but it has taken until now for experts to determine the sex of the 'lovers ' . Now , researchers believe they have come up with a way to tell fossils of small feathered male dinosaurs from those of females . They say that the key differences between the sexes lie in bones near the base of the tail . Paleontologistsat the University of Alberta examined a pair of fossils found in Mongolia , which were first described in 2001 . One is a complete skeleton , while the other is missing the middle and end of its tail . the researchers looked at indirect evidence of sexually dimorphic display structures , which are evident today in birds . Examples include the fans of peacocks , the tall crests of roosters or the long tail feathers of some birds of paradise , which are used to attract and court mates . They are almost always much larger in males who do the courting , than in females , who do the choosing . The team theorised that like birds , small feathered dinosaurs such as oviraptors used long feathers on their tails to attract mates , rather than for flying . Some stegosaurus individuals have been found with wide plates while others had tall plates with a sharper tip that were 45 per cent smaller . Experts believed that these may have been two distinct species or individuals of a different age . However , using modern scanning techniques on a group of stegosaurus discovered at a 'graveyard ' in central Montana , scientists have unraveled the answer . They found dinosaurs that had both sets of plates in the graveyard , suggesting they lived side-by-side . Apart from the different plates , their skeletons were identical . This makes it unlikely that they were different species and CT scanning has shown that the bones were not morphing into one or the other . This suggests they belonged to two different sexes instead . The research team believe that the males may have had the larger , broader plates for use in mating displays while the females had the sharper taller plates , that may have helped to discourage unwanted attention or predators . Evan Saitta , who conducted the work at the University of Bristol , said : 'As males typically invest more in their ornamentation , the larger , wide plates likely came from males . 'These broad plates would have provided a great display surface to attract mates . 'The tall plates might have functioned as prickly predator deterrents in females . ' Stegosaurus , a herbivorous dinosaur , lived around 150 million years ago during the late Jurassic period in the western United States . Along with its bony back , it also had large spikes on its tail that are thought to have been for defence or fights with rivals . Stegosaurus ( above ) lived around 150 million years ago but scientists have been baffled by differences between the shape of the plates on some fossils - leading some to believe they were different species . The new research on the armoured plates may help scientists determine whether 'Sophie ' , the stegosaurus at the Natural History Museum in London pictured above , really is a female or if it was in fact a male dinosaur . Some dinosaur experts have speculated that the bony plates may have been covered in skin filled with blood vessels so they could flush with colour . This could have acted as a warning to predator or being used as a way of attracting attention of the opposite sex . Most dinosaur remains are difficult to determine the sex but there are a few that have been found to exhibit differences between males and females . Some had large crests or nose horns that may have been sexual features . Professor Paul Barrett , a palaeontologist at the Natural History Museum in London where one of the most complete stegosaur skeletons has just gone on display , said : 'It is interesting because it would add to the debate on what the plates were for . 'Sexual dimorphism is something we see a lot in modern animals , although it 's not particularly prevalent in living reptiles or in living birds . ' However he added : ' I 'd like to see a lot more information on the graveyard site itself , the different sizes of the specimens , how they were arranged in the ground , more detail on the geology , and on the analyses that were done . ' Evan Saitta ( shown left with a stegosaurus armoured plate , used a CT scanner to examine the plates to see whether they might belong to different sexes . He is shown on the right cutting into the fossil to take samples .
Stegosaurus specimens have been found with three different types of plate along their snout - large broad plates and taller sharper plates that are smaller . researchers long believed they belonged to separate species of stegosaurus . New researchers found the different shapes may distinguish males and females . Palaeontologists say the plates could have been used to help locate a mate .