Tyrannosaurus rex might be the most feared dinosaur to ever walk the Earth, but there was once another T. rex that terrorised the ancient seas.
Named Tylosaurus rex, this fierce creature is a massive new species of mosasaur, a family of marine reptiles that lived during the reign of the dinosaurs.
Tylosaurus rex, or T. rex for short, could grow to up to 43 feet (13.1 metres) in length.
That makes Tylosaurus rex more than twice the length of the largest great white sharks, and just as big as the land-based T. rex.
Scientists say that Tylosaurus rex, whose name means ‘King of the Tylosaurs’, was one of the biggest mosasaurs to ever exist.
According to palaeontologists, these terrors had exceptionally strong neck and jaw muscles as well as a mouth full of razor-sharp, finely serrated teeth.
Experts think that would have made them top predators in the seas above what is now Texas around 80 million years ago.
‘Everything is bigger in Texas and that includes the mosasaurs, apparently,’ says lead researcher Dr Amelia Zietlow, from the American Museum of Natural History.
Tylosaurus rex, or T. rex for short, was a marine reptile that terrorised the ancient seas 80 million years ago
The fossil remains of Tylosaurus rex have actually been sitting in several museums around the US for decades, but no one had realised what they really were.
Dr Zietlow was looking through the archives at the American Museum of Natural History when she stumbled upon a mosasaur fossil that appeared to have been misidentified.
The fossil had been labelled as a specimen of Tylosaurus proriger, another large mosasaur discovered over 150 years ago.
However, when Dr Zietlow compared the fossil to the name-bearing specimen, known as the holotype, it was clear that this fossil was something different altogether.
The mysterious mosasaur is much larger than Tylosaurus proriger, with a skull almost as big as Dr Zietlow herself.
Likewise, Tylosaurus proriger fossils are found in what is now Kansas and date back to around 84 million years ago, while these were from Texas and are four million years younger.
Dr Zietlow and her colleagues soon realised that they had discovered a previously unrecognised species of mosasaur, which included more than a dozen similarly mislabelled fossils held at various institutions.
Their holotype specimen for the new species is a truly giant specimen nicknamed ‘The Black Knight’, which was first discovered in 1979 along an artificial reservoir near Dallas.
These monsters could grow up to 43 feet (13.1 metres) in length. That makes Tylosaurus rex more than twice the length of the largest great white sharks, and just as big as the land-based T. rex.
Scientists found that Tylosaurus rex was much larger than other mosasaur species and had unique serrated teeth
In a paper, published by the Bulletin of the American Museum of Natural History, scientists say that this would have been the ‘top predator of its domain’.
At this time, North America was almost divided in half by a warm shallow sea called the Western Interior Seaway, plunging most of Texas underwater.
Dr Zietlow says this would have been ‘home to a variety of sea monsters, including sea turtles, mosasaurs, plesiosaurs, and fish’.
But T. rex didn’t appear to have been fussy about its diet, as its teeth aren’t clearly specialised for one specific type of prey like other mosasaurs are.
‘Tylosaurus rex differs from other Tylosaurus in part by having serrated teeth and features of the skull that suggest stronger jaw and neck muscles,’ says Dr Zietlow.
‘I think it was using those tools to help it process larger prey by ripping things to pieces.’
But the Tylosaurus rex wasn’t just a danger to other creatures; it could also be a deadly threat to members of their own species.
‘Mosasaurs in general seemed to have been pretty aggressive towards one another,’ says Dr Zietlow.
T. rex had exceptionally strong neck and jaw muscles, which would have made it the ‘top predator of its domain’
‘I can think of at least one where another mosasaur’s tooth is still embedded in a Mosasaurus jaw.’
However, Tylosaurus rex appeared to push these aggressive tendencies to a new level.
Ron Tykoski, vice-president of science and curator of vertebrate palaeontology at the Perot Museum, says: ‘Besides being huge… T. rex appeared to be a much meaner animal than other mosasaurs.
‘Through our study and examination of well-preserved fossils collected throughout the north Texas region, we have evidence of violence within this species to a degree not previously seen in other Tylosaurus specimens.’
The impact of these aggressive tendencies can clearly be seen on the Black Knight, which is missing the tip of its snout and has a fractured jaw.
Researchers say these massive wounds could only have been inflicted by another member of its own species.
Besides offering a fascinating glimpse of a terror from the distant past, this discovery is helping to clear up the tangled story of mosasaur evolution.
In the past, Dr Zietlow says that mosasaurs have been considered a ‘boring’ group with very limited diversity.
These creatures were extremely aggressive to other members of their species, and fossils show massive wounds from their battles
However, as scientists pick apart the subtle differences between fossil specimens, an unexpectedly complex picture is starting to emerge.
Dr Zietlow adds: ‘I think it shines a spotlight on how diverse mosasaurs as a group really are.
‘We have identified many new features of mosasaur anatomy.
‘When taken into account in our analyses of their evolutionary relationships, they paint a very different picture than what was known for the last 30-ish years.’
