A fossil of a new dinosaur with short forearms like the Tyrannosaurus rex suggests their disproportionate size served a purpose.
Scientists think the carnivorous beasts used their tiny appendages to grab onto each other while mating, or to help them get up after a fall.
the new dinosaur, Meraxes gigaslived millions of years apart from the infamous T. rex and does not appear to be a close relative.
The fossil was studied by researchers at the Ernesto Bachmann Paleontological Museum in Neuquén, Argentina after it was discovered in Patagonia.
They also found that the species had a large, bumpy skull, which it probably used for hunting.
Project leader Dr Juan Canale said: ‘Actions related to predation were most likely carried out by the head.
‘I tend to think that their arms were used in other activities.
“Maybe they used the arms for reproductive behavior, such as holding the female while mating or supporting themselves to get back up after a break or a fall.”
Fossils suggest the Meraxes gigas (pictured) was 36 feet (11 meters) long and weighed 4 tons
Reconstruction of the Meraxes gigas skeleton with recovered bones in white. A: Left half of the skull, B: Right scapulocoracoid, C: Right complete pelvis, D and E: Tail vertebrae, F: Left articulated tibia and fibula, G: Left femur, H: Left astragalus and calcaneum, I: Left foot, J: Articulated right arm. Individual scale bars, 10 cm; general scale bar, 1 m
Bones of Meraxes gigas. A: right side of skull, B: articulated right arm, C: sacrum, D: left foot
Tyrannosaurs rex (pictured) was a type of bird-like, carnivorous dinosaur. It lived between 68-66 million years ago in what is now the western side of North America
WHAT ARE THEROPODES?
Theropod means “beast on foot” and denotes a dinosaur belonging to a diverse group of large bipeds.
They include the largest terrestrial carnivores to ever shake the earth, including the T Rex, as well as the newly discovered Meraxes gigas.
Theropods first appeared during the Carnic epoch of the late Triassic, 231 million years ago, and include all large terrestrial carnivores from the early Jurassic to at least the late Cretaceous, about 66 million years ago.
Recent theories propose that the body size of theropods continuously shrank over a period of 50 million years, from an average of 359 lb (163 kg) to 1.8 lb (0.8 kg).
Modern birds are actually the descendants of small flightless theropods.
The largest surviving theropod is the common ostrich.
The fossilized bones of the Meraxes gigas † named after a dragon from Game of Thrones – shows it was 11 meters long and weighed 4 tons.
The specimen lived 90 million years ago in Argentina’s current northern region of Patagonia and died at about age 45.
His forearms were about 47 percent of the length of his femur.
dr. Canale added: ‘We found the perfect spot on the first day of searching, and Meraxes was found.
“It was probably one of the most exciting moments of my career.
“The fossil has a lot of new information and it is in excellent condition.”
‘The fossil of’ Meraxes never-before-seen shows, complete parts of the skeleton like the arms and legs that helped us understand some evolutionary trends and the anatomy of Carcharodontosaurids – the group it belongs to.”
Carcharodontosaurids are a group of mostly large, bipedal dinosaurs in the theropod dinosaur clade.
The bigger their heads, the smaller their arms became, a pattern also seen in T. rexes whose forearms were only about a meter long.
Fossil data also suggest that the Meraxes gigas came from a large family, before dying out in the late Cretaceous period.
“The group flourished and reached a peak of diversity shortly before they became extinct,” said Dr. Canale.
The bones of the Meraxes gigas were discovered at the Huincul Formation paleontological site in the Neuquén Basin in northern Patagonia, Argentina
dr. Canale said: ‘We found the perfect spot on the first day of searching and Meraxes was found. It was probably one of the most exciting moments of my career.’
The study, published today in Current Biologyconcludes that the T. rex and the Meraxes gigas evolved to have their small arms completely separated.
The latter died out nearly 20 million years before the emergence of the former, and they are also very far apart on the evolutionary tree.
However, the fact that the trait of shortened forelimbs is shared suggests that they have some sort of survival advantage.
They are not thought to have evolved to be short because they were unable to use the predators, as fossil evidence shows they were attached to powerful muscles.
“I’m convinced that those relatively small arms had some function,” said Dr. Canale.
‘The skeleton shows large muscle insertions and fully developed chest girdles, so the arm had strong muscles.
“It means the arms don’t shrink because they were useless to the creatures.
‘The more difficult question is what exactly were the functions. Sex and balance are most likely.”
The Meraxes gigas skull was decorated with crests, grooves, humps and small horns, and were probably there to attract potential mates.
dr. Canale said: ‘These decorations appear late in development as the individuals matured.
Sexual selection is a powerful evolutionary force. But since we cannot directly observe their behavior, there is no certainty about that.’
T Rex (left) and the Meraxes gigas (right) have evolved to have their small arms completely separate. The skull of Meraxes gigas was decorated with crests, grooves, humps and small horns, which were probably there to attract potential mates
Dinosaur with oldest EVER ‘navel’ that attached egg yolk sacs to is discovered in 125-million-year-old fossil from China
The oldest navel ever found by paleontologists on a 125-million-year-old fossil of a biped in China†
The barely noticeable navel spot belongs to a reptile in the genus psittacosaurus who lived in the Cretaceous.
Researchers note that dinosaurs did not have umbilical cords, unlike humans, because they laid eggs.
Instead, dinosaurs’ yolk sac was attached directly to the body through a slit-like opening, which is also found in other egg-laying land animals.
It is this opening that closed around the time the animal hatched, leaving behind a distinctive long navel scar.
A 3D reconstruction of a supine Psittacosaurus with the long umbilical cord scar surrounded by distinctive scales identified by the research team
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