MEANING: Alxa lizard
PERIOD: Early Cretaceous
CONTINENT: Asia
Alxasaurus is a therizinosauroid theropod dinosaur from the Early Cretaceous of China. Several specimens are known and they vary in size, but its maximum adult length is estimated up to 4 m and mass up to 400 kg. Alxasaurus is among the earliest known members of the Therizinosauroidea, but it already possessed the body shape, including the long neck, short tail, and relatively large claws, of later therizinosauroids. Like other members of this group, it was a bipedal herbivore with a large gut to process plant material.
Alxasaurus is from the Cretaceous. The Cretaceous is a geological period that lasted from about 145 to 66 million years ago. It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of the entire Phanerozoic. The name is derived from the Latin creta, "chalk", which is abundant in the latter half of the period.
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct flora and fauna, while dinosaurs continued to dominate on land. The world was ice free, and forests extended to the poles. During this time, new groups of mammals and birds appeared. During the Early Cretaceous, flowering plants appeared and began to rapidly diversify, becoming the dominant group of plants across the Earth by the end of the Cretaceous, coincident with the decline and extinction of previously widespread gymnosperm groups.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction that lies between the Mesozoic and Cenozoic Eras.
Alxasaurus is a therizinosaur. Therizinosauria is a family of large herbivorous theropod dinosaurs from the Middle Jurassic to Late Cretaceous deposits of Europe, Asia, and North America. They spanned a large range of sizes, from the Jianchangosaurus at about 2 m in length, to the 10 m long Therizinosaurus.
Therizinosaurs had a very distinctive set of characteristics. Their long necks, wide torsos, and hind four-toed feet resembled those of basal sauropodomorph dinosaurs. Among the most striking characteristics of therizinosaurs are the enormous claws on their hands, which reached lengths of around one meter in Therizinosaurus. The wide range of motion in the forelimbs also supports the idea that they were mainly herbivorous. They may have used their long reach and strongly curved claws to grasp and shear leafy branches. Skin impressions from Beipiaosaurus indicate that therizinosaurs were covered with a coat of primitive, down-like feathers, as well as longer, simpler, quill-like feathers that may have been used in display.