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Why did Tyrannosaurus rex have short arms?





Skeletons of the dinosaur Tyrannosaurus rex (T-rex) show that it had short arms. Why did Tyrannosaurus rex have short arms instead of no arms or longer limbs? A carnivorous dinosaur skeleton found in South America may have the answer.

Skeleton remains of a Gualicho shinyae – a medium-sized two-legged theropod dinosaur, weighing about 1,000 pounds (450 kilograms), had forelimbs about the size of a human child’s arms – and is similar to T-rex even though they developed independently of each other.

The Gualicho shinyae is referred to as the Argentinean non-T-rex. T-rex is much larger and weighs 6,000 pounds (2,720 kilograms). The Gualicho lived about 90 million years ago during the mid-Cretaceous period, whereas T-rex lived about 60 million years ago. Therefore they did not meet each other even though they lived in the same region. T-rex is pictured above and Gualicho shinyae is pictured below (artists interpretation).



Like T-rex, the Gualicho shinyae had just digits on its hands – a thumb and a forefinger. The incomplete skeleton was discovered in 2007 during an excavation in northern Patagonia in South America.

Palaeontologists say the similarities of the two dinosaurs is an example of convergent evolution: the development of identical traits in unrelated species due to natural selection.

Therefore the small forelimbs – short arms – on a carnivorous (meat-eating) dinosaur – was there for a reason, but scientists are still unsure why. ‘By learning more about how reduced forelimbs evolved, we may be able to figure out why they evolved,’ said Dr. Peter Makovicky from The Field Museum in Chicago. He said it was an unusual feature of carnivorous dinosaurs because it is different from other carnivorous dinosaurs found in the same rock formation. The Gualicho shinyae appears to be mostly related to Deltadromeus, a leggy carnivorous dinosaur with slender arms from Africa.

The name Gualicho is the Argentinean term for ‘bad luck’ because the palaeontologists who discovered the dinosaur had an accident in which a truck carrying the skeleton over-turned (no one was hurt).




http://www.mirror.co.uk/news/world-news/tiny-arms-fearsome-rex-dinosaur-8415165




MARTINA NICOLLS is an international aid and development consultant, and the author of:- The Shortness of Life: A Mongolian Lament (2015), Liberia’s Deadest Ends (2012), Bardot’s Comet (2011), Kashmir on a Knife-Edge (2010) and The Sudan Curse (2009).
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