Therizinosaurus

Therizinosaurus meaning 'scythe lizard' was a very large genus of therizinosaurid dinosaurs that lived during the Late Cretaceous period in what is now Asia. It was known from the fossiliferous Nemegt Formation. The first remains of Therizinosaurus were found in 1948 by a Mongolian field expedition in the Gobi Desert and later described by Evgeny Maleev in 1954. This dinosaur stood out because of its very long, stiffened claws on its forelimbs.

Therizinosaurus could grow up to 9–10 m (30–33 ft) long and 4–5 m (13–16 ft) tall, and may have weighed over 5 t (5.5 short tons). It had long neck and a wide body, which would have helped it eat leaves high up in trees. Its forelimbs were very strong and had three fingers with extremely long claws, the longest known of any land animal, reaching above 50 cm (20 in) in length. These claws were likely used for pulling vegetation within reach rather than for attack or defense because they were too fragile for fighting.

Therizinosaurus was one of the last and largest members of its unique group, the Therizinosauria. For many years, scientists were unsure where it fit among dinosaurs, but it is now placed among the Theropoda, specifically as maniraptorans. Its unusual body shape shows how different species can evolve similar traits to adapt to their environment, much like some herbivorous mammals. Despite its imposing claws, Therizinosaurus was probably a peaceful browser, using its arms to reach high foliage and stay safe from predators like tyrannosaurid Tarbosaurus.

History of discovery

In 1948, scientists from the USSR Academy of Sciences explored the Nemegt Formation in the Gobi Desert of Southwestern Mongolia looking for fossils. They found many dinosaur and turtle fossils, including three large claw bones from the hands of a dinosaur. These claws were described in 1954 by a scientist named Evgeny Maleev, who named the dinosaur Therizinosaurus cheloniformis. The name means “scythe lizard” because of its large hand claws, and “cheloniformis” refers to its turtle-like appearance.

Later, more fossils were found, including parts of the arms and legs. These discoveries helped scientists understand that Therizinosaurus was a type of theropod dinosaur, not a turtle. The new fossils showed that it had long, powerful arms with huge claws, and they confirmed it belonged to a group of dinosaurs known as therizinosaurs.

Description

Therizinosaurus was one of the largest therizinosaurid dinosaurs, reaching lengths of 9 to 10 meters (30 to 33 feet). Estimates suggest it weighed between 5 to 10 tons, comparable to an elephant. It had a small skull with a beak-like apparatus on top of a long neck, walked on two legs, and likely had sparse feathers.

The most striking feature of Therizinosaurus were its enormous claws on each hand, which were the longest known from any land animal. Its arms were very long, and its body was built for processing plant material, indicating it was a herbivore. The legs were sturdy, and its feet had four weight-bearing toes, unlike most other theropods which usually had three.

Classification

See also: Timeline of therizinosaur research

Evgeny Maleev first thought Therizinosaurus was a giant marine turtle. Later, scientists began to realize it was actually a type of theropod dinosaur. In 1970, Anatoly Rozhdestvensky suggested that what looked like ribs in the main fossil might have come from another dinosaur. By the 1990s, discoveries like Alxasaurus helped scientists understand that Therizinosaurus and similar dinosaurs were unusual theropods, related to birds. These dinosaurs had long, powerful claws and feathers, showing they were part of the group that includes birds today.

Paleobiology

Scientists have studied how Therizinosaurus might have lived and eaten. In the 1990s, researchers noticed that Therizinosaurus and some ancient mammals had similar body shapes, with strong arms and robust legs. They believed these features evolved separately but served the same purpose. Because animals with such bodies are usually plant-eaters, they thought Therizinosaurus probably ate leaves from trees and shrubs. Its long neck would have helped it reach high branches, and its long arms could have been used to grab food.

More recent studies have looked at the function of Therizinosaurus's famous long claws. When the dinosaur was first discovered in 1954, some scientists thought the claws were for grabbing seaweed. Others suggested they could have been used to open insect nests, dig in soil, or defend against predators. Modern computer simulations show that the claws were likely too weak for heavy digging but might have been good for pulling or grabbing plants. Some scientists even think the claws were mostly for show and not for any specific job, growing larger as the dinosaur got bigger.

Paleoenvironment

The remains of Therizinosaurus were found in the Nemegt Formation in the Gobi Desert. This area had many rivers and forests, with a climate that had wet and dry seasons. The environment supported many different kinds of dinosaurs, including herbivorous ones like Therizinosaurus.

Other dinosaurs that lived in the same area included Deinocheirus, Saurolophus, Nemegtosaurus, and the large predator Tarbosaurus. Because of its great height, Therizinosaurus likely had access to food that other dinosaurs could not reach. Its long claws might have helped it defend itself against predators.