New dinosaur fossils with short arms show they could have provided grip during mating
A new fossil of a dinosaur with short arms like Tyrannosaurus rex suggests that its disproportionate size served a purpose.
Scientists think the carnivorous animals may have used their tiny appendages to grip one another during mating, or to help them stand up after falling.
new dinosaur, Meraxes gigaslived millions of years apart from the infamous T. rex and were apparently not close relatives.
The fossil was studied by researchers at the Ernesto Bachmann Museum of Paleontology in Neuquén, Argentina after it was discovered in Patagonia.
They also found the species had a large, bumpy skull, possibly used for hunting.
Project leader Dr Juan Canale said: ‘Actions related to predation are most likely carried out by the head.
‘I tend to think their arms are used in other kinds of activities.
‘They may have used their arms for reproductive behaviors such as holding the female during mating or supporting themselves to stand back up after a rest or fall.’
Fossils suggest Meraxes gigas (pictured) is 36 feet (11 meters) long and weighs 4 tons
Reconstruction Meraxes gigas skeleton showing recovered bones in white. A: Left skull, B: right scapulocoracoid, C: right complete pelvis, D and E: caudal vertebrae, F: tibia and fibula left articulation, G: left femur, H: astragalus and left calcaneum, I: left leg, J: Articulated right arm. Individual scale rods, 10 cm; common scale bar, 1 m
Bones of Meraxes gigas. A: Right side of skull, B: Articulated right arm, C: Sacrum, D: Left leg
Tyrannosaurus rex (pictured) was a species of bird-like flesh-eating dinosaur. It lived between 68–66 million years ago in what is now the western side of North America
Fossil bones from Meraxes gigas – named after the dragon from Game of Thrones – show that it is 36 feet (11 meters) long and weighs 4 tons.
The specimen lived 90 million years ago in present-day Argentina’s northern Patagonia region, and died at about 45 years of age.
His forearm is about 47 percent of the length of his femur.
Dr Canale added: ‘We found the perfect spot on the first day of the search, and Meraxes found.
“It was probably one of the most exciting points of my career.
‘The fossil has a lot of new information, and it’s in very good shape.’
‘Fossil from Meraxes showing never before seen, complete regions of the skeleton, such as arms and legs that helped us understand some of the evolutionary trends and anatomy of the Carcharodontosaurids – their group.’
Carcharodontosaurids were a group of mostly, bipedal dinosaurs in the theropod dinosaur clade.
The bigger their head, the smaller their arms, which is a pattern also seen in T. rexes whose forearms are only about three feet long.
The fossil record also shows Meraxes gigas came from a large family, before becoming extinct in the Late Cretaceous period.
‘This group evolved and reached a peak of diversity just before it went extinct,’ says Dr Canale.
Meraxes gigas bones found at the paleontological site of the Huincul Formation in the Neuquén Basin in northern Patagonia, Argentina
Dr Canale said ‘We found the perfect spot on the first day of the search, and Meraxes was found. It was probably one of the most exciting points of my career.’
The study, published today in Current Biology, concluded that T. rex and Meraxes gigas evolved to have their little arms completely separated.
The latter died nearly 20 million years before the appearance of the former, and they are also very far apart on the evolutionary tree.
However, the fact that the shorter forelimbs share a common feature suggests that they did have some sort of survival advantage.
It is thought they did not evolve to be short because they were not used to predators, as fossil evidence suggests they were attached to strong muscles.
‘I believe the well-proportioned little arm has some kind of function,’ says Dr Canale.
‘The skeleton shows large muscle insertions and the chest girdle is fully developed, so the arms have strong muscles.
‘That means the arm isn’t shrinking from being of no use to the creature.
‘The more difficult question is what exactly it does. Sex and balance most likely.’
It Meraxes gigas the skull is decorated with crests, grooves, ridges and small horns, and is probably there to attract potential mates.
Dr Canale said: ‘The ornaments appear late in development as the individual matures.
‘Sexual selection is a powerful evolutionary force. But given that we cannot directly observe their behavior, it is impossible to be certain about this.’
T Rex (left) and Meraxes gigas (right) evolved to have their little arms completely separated. The skull of the Meraxes gigas was decorated with crests, grooves, protrusions, and small horns, which were probably there to attract potential mates.
Dinosaur with oldest ‘navel’ to which the yolk sac of the egg was attached found in 125 million year old fossil from China
The oldest navel ever found by paleontologists in a 125-million-year-old biped fossil in China.
The barely visible navel mark belongs to the reptiles in the genus Psittacosaurus who lived in the Cretaceous.
The researchers noted that dinosaurs did not have umbilical cords, unlike humans, because they laid eggs.
In contrast, the yolk sac of dinosaurs 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 seals at the time the animal hatches, leaving a long umbilical scar.
Read more here
3D reconstruction of a reclining Psittacosaurus showing a long umbilical scar surrounded by distinctive scales identified by the research team
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