Chilantaisaurus

Chilantaisaurus ("Jilantai Salt Lake lizard") is an extinct genus of large theropod dinosaur that lived in present-day China during the Late Cretaceous period. It was described by Chinese paleontologist Hu Show-Yung in 1964. The genus contains a single valid species, C. tashuikouensis, though several other species have been assigned to the genus. C. tashuikouensis is known from a single, incomplete postcranial skeleton, the holotype specimen. This specimen was found by a joint Sino-Soviet expedition to Inner Mongolia in rock layers coming from the Ulansuhai Formation. These rock layers are thought to date to the Santonian or Campanian stages of the Cretaceous period, around 85.7 to 72.2 million years ago. However, the age of the Ulansuhai Formation is debated.

Chilantaisaurus was around 11 metres (36 ft) in length and weighed 2.5–4 metric tons (2.8–4.4 short tons). This makes it among the largest known theropod genera, comparable to Tyrannosaurus. The forelimbs of Chilantaisaurus are only known from a humerus and a manual ungual (hand claw); this humerus is one of the largest humeri known from a theropod dinosaur. It measures 580 millimetres (23 in) in length and has a greatly expanded deltopectoral crest. The ratio between the humerus and femur length is very high, in contrast to those of carcharodontosaurids like Mapusaurus but comparable to those of spinosaurids like Suchomimus. The hindlimbs were long with a robust metatarsus, the largest known of any purported megaraptoran or Neovenator itself.

The classification of Chilantaisaurus has been in flux since its original description. Hu believed it was a member of Carnosauria; later studies have challenged this notion. While some studies suggested it was a member of Spinosauridae, others have proposed that Chilantaisaurus was a coelurosaur, possibly related to Megaraptora, or a carcharodontosaurian related to genera like Neovenator. The Ulansuhai Formation is dominated by red mudstone and siltstone, indicating a floodplain environment defined by meandering rivers. Other dinosaurs known from this site include the ornithomimosaurSinornithomimus and the pachycephalosaurSinocephale.