Probactrosaurus
Probactrosaurus (meaning "before Bactrosaurus") is an early herbivorous hadrosauroid iguanodont dinosaur. It lived in China during the Late Cretaceous period.
In 1959 and 1960 a Soviet-Chinese expedition uncovered the remains of a euornithopod in Inner Mongolia near Maortu. The type species is Probactrosaurus gobiensis, described and named by A. K. Rozhdestvensky in 1966.[1] The generic name refers to Rozhdestvensky's hypothesis that Probactrosaurus would be the direct ancestor of Bactrosaurus, a notion now discarded.
The specific name refers to the Gobi desert. The holotype specimen, PIN 2232/1, a partial skeleton with skull, was found in layers of the Dashuigou Formation. Another partial skeleton, PIN 2232-10, was found along with numerous other fragments.[1]
In 1966 Rozhdestvensky also named a second species, Probactrosaurus alashanicus, based on fragmentary material. Its specific name refers to the Alxa League. In 2002 David B. Norman published a revision of the genus, in which he reported the holotype specimen of P. alshanicus, the back of a skull, had been lost after being dispatched from Moscow to Beijing. He concluded that the species was a synonym of P. gobiensis.[2]
In 1997 Lü Junchang named a third species, Probactrosaurus mazongshanensis, based on holotype IVPP V.11333 found in 1992. The specific name refers to the Mazong Shan region.[3] Today, this form is seen as more closely related to Equijubus and Altirhinus rather than to P. gobiensis and is therefore commonly referred to as "Probactrosaurus" mazongshanensis.[2] It was moved to the new genus Gongpoquansaurus in 2014.[4]
Probactrosaurus was a herbivorous dinosaur. In 2010 Gregory S. Paul estimated its length at 5.5 metres (18 feet) and its weight at one tonne.[5] Probactrosauurus was lightly built, with relatively long and slender arms and hands and only a small thumb spike. It had a narrow snout, an elongated lower jaw and tooth batteries, each consisting of a superimposed double row of flattened cheek teeth; a third row of replacement teeth was incipient. Probably predominantly quadrupedal, it shared some common features with the later duck-billed dinosaurs.[6]
