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During the Triassic period, the rauisuchid predator ruled the land while the phytosaur was the master of the sea - and experts have long believed the two large reptiles lived separate lives.

But, a tooth found embedded in the leg bone of the land-dwelling rauisuchid may cast doubts on this theory. 

The 220-million-year old tooth is said to have belonged to the semi-aquatic phytosaur and was left in the thigh bone following a savage battle between the two creatures.

To study the tooth, without destroying the bone, researchers used computed tomography (CAT) scans to build a 3D model of it (pictured in blue). A selection of other, fossilised phytosaur teeth are pictured. The tooth was found in the bone of a rauisuchid, a large land reptile. Until now, experts did not think the creatures interacted

And multiple wounds suggest the two beasts may have clashed regularly, despite their different habitats.

Rauisuchids typically had large heads, sharp teeth, long hind legs, and scales on their backs.

They measured up to 25ft (7.6 metres) tall, with 2ft (0.6 metres) long heads.

By comparison, the phytosaur, which means 'plant lizard', typically grew to 6ft (2 metres) long. 

Professor Stephanie Drumheller, of the University of Tennessee at Knoxville, said: 'To find a phytosaur tooth in the bone of a rauisuchid is very surprising.

'These rauisuchids were the largest predators in their environments.

'You might expect them to be the top predators as well, but here we have evidence of phytosaurs, who were smaller, semi-aquatic animals, potentially targeting and eating these big carnivores.'

CLASH OF THE PREHISTORIC TITANS 

A model skeleton of a phytosaur is pictured in the Petrified Forest National Park, Arizona. Experts believe the semi-acquatic creatures had 166 teeth and were predators of the Middle and Upper Triassic

Rauisuchids typically had large heads, sharp teeth, long hind legs, and scales on their backs.

They measured up to to 25ft (7.6 metres) long, with 2ft (0.6 metres) long heads.

They were considered one of the most dangerous predators of the Middle and Upper Triassic.

Rauisuchids were reptiles, but they resembled dinosaurs so closely that they are often mistaken for dinosaur ancestors.

By comparison, phytosaurs resembled modern-day crocodiles.

They had short legs, wide, heavy bodies with rows of armoured scales, long tails, and long toothy snouts.

These teeth were sharp and cone-shaped.

The name phytosaur means 'plant lizard', and they typically grew to 39ft (12 metres) long.

They were considered one of largest water predators of the Triassic Period. 

Although the bone was dug up in the western United States, at the time the Triassic reptiles would have been roaming the super continent Pangea, which was just beginning to break up into the individual land masses we see today.

It challenges beliefs about the lifestyles of these ancient creatures, who were distant relatives of modern-day crocodiles that would have towered over the early dog-sized dinosaurs.

Some lived on land, while others lived in water - and it was believed, until now, that they didn't interact.

The analysis of the bite marks in two thigh bones suggests both predator species at the top of their respective food chains not only crossed paths, but the smaller creature may have potentially eaten the larger.

Rauisuchids typically had large heads, sharp teeth, long hind legs, and scales on their backs.They measured up to 25ft (7.6 metres) tall, with 2ft (0.6 metres) long heads. The polonosuchus - a genus of rauisuchian - is pictured

The bones are stored at the University of California Museum of Paleontology, Berkeley.

To study the tooth, without destroying the bone, the researchers used computed tomography (CAT) scans to build a 3D model.

This, along with an examination of the bite marks, revealed a story of multiple struggles.

The team found tissue surrounding the bite marks revealed the rauisuchid was attacked twice and survived.

But, evidence of crushing, impact and flesh-stripping, without healing, showed the animal later died in another attack.

By comparison, the crocodile-like phytosaur, which means 'plant lizard', typically grew to 6ft (2 metres) long. This image is an illustration of the belodon - a genus of the phytosaur

Professor Drumheller said: 'Finding teeth embedded directly in fossil bone is very, very rare.

'This is the first time it has been identified among phytosaurs, and it gives us a smoking gun for interpreting this set of bite marks.'

The findings also suggest previous distinctions between water and land-based food chains from this time, the Late Triassic Period, might be built upon mistaken assumptions made from fossil remains.

Palaeontologist Dr Michelle Stocker, of Cirginia Tech, added: 'This research will call for us to go back and look at some of the assumptions we have had in regard to the Late Triassic ecosystems.

'The aquatic and terrestrial distinctions made were oversimplified, and I think we have made a case the two spheres were intimately connected.'

The research also calls into question the importance of size in a fight.

Added Professor Drumheller: 'Both of the femora we examined came from some of the physically largest carnivorous species present at both locations.

'Yet they were targeted by other members of the region, specifically phytosaurs. Thus, size cannot be the only factor in determining who is at the top of the food chain.'