Image copyright Ozzelle Center for Paleontology Image caption The dinosaur’s remains were found in a sediment layer 96m below the ground in a quarry in the west of the US
Scientists say they have discovered fossilised remains of a prehistoric dinosaur that was the size of a medium-sized dog.
The Pachyrhinosaurus is well known in literature and art, but the discovery expands on the medium and large sizes of the species.
The young dinosaur was a growth spurt from another dinosaur that had already gone extinct.
The new species is also the largest known to have lived in the Triassic period, 139 million years ago.
“Its size was quite remarkable,” said palaeontologist Matthew Lamanna, a vertebrate palaeontologist at the Carnegie Museum of Natural History in Pittsburgh.
Image copyright Ozzelle Center for Paleontology Image caption The animal’s skeleton was found in 23 million-year-old sediments
The creature’s skeleton was found in 23 million-year-old sediments in a quarry in West Texas.
To get to the bones, researchers had to travel 5km (3.1 miles) in a tricorder, or tricera, – a deep-sea submersible.
“You are travelling for five days with your tricera on a completely virgin terrain, usually covered in sediment,” Dr Lamanna explained.
In that entombed environment, a huge collection of animal remains – including Triceratops, sabre-toothed cats and stegosaurs – were discovered by Dr Lamanna and colleague Peter Makovicky.
It was then that they spotted the Pachyrhinosaurus alongside this incredible collection.
Pachyrhinosaurus was well known in literature and art, but a total lack of palaeontological records from the Upper Jurassic meant it was seen more as an illustrative animal than a fossil.
“We saw two species that were part of the same family and both went extinct,” Dr Lamanna said.
Image copyright Ozzelle Center for Paleontology Image caption Pachyrhinosaurus’s palaeontological record was not complete, and very few skeletons were found
Another challenge Dr Lamanna and his team faced was the lack of palaeontological records from the Upper Jurassic.
Palaeontologists are often loathe to dig up new species because their fossils may disappear into a mud bog, underwater or buried in soil.
With less data on this new dinosaur, the team from Carnegie Museum of Natural History had to go back as far as the Paleozoic period, 150 million years ago, to find signs of the creature.
“Although we weren’t sure it was going to survive, we went all the way back to the Paleozoic and even before that,” said Dr Lamanna.
Image copyright Ozzelle Center for Paleontology Image caption The species lived in an area along the US-Mexico border
In the process, scientists discovered a complete skeleton, including teeth and bones of bony “house teeth”.
Such teeth are seen in a wide range of animals.
Pachyrhinosaurus is the largest known to have lived in the Triassic period, 139 million years ago.
The news comes as the Americans and Mexican state governors agreed on Friday to develop a plan to stem the flow of people trying to cross the country illegally.
Armed migrant groups cross into the US illegally.
The plan proposes working with governors in border states, and will also propose greater regional law enforcement and improved border security to stem the flow of migrants.
US officials will also seek changes to the Immigration and Nationality Act, which allows citizens of countries other than Mexico and Canada to apply for an H-1B visa, which gives foreigners a temporary visa.
Image copyright Shutterstock Image caption Defying previous pleas, the Mexican government turned down President Donald Trump’s request for $3.6bn (£2.9bn)
Meanwhile, Mexican President Enrique Pena Nieto is likely to turn down US President Donald Trump’s request for $3.6bn (£2.9bn) in additional aid.
The dispute has flared up over Mexico’s decision to honour a temporary visa programme and not comply with a border wall that Mr Trump has proposed.
Pena Nieto is pushing for Mexico to maintain ties with the US and has repeatedly sent the US leader clear messages that there is nothing to gain in trashing the two countries’ relationship.
At least four other governors have also expressed their opposition to changing the visa policy.
According to the Associated Press, Pena Nieto will not meet Trump until he receives an official State of the Union address, which is traditionally delivered by the US president.