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Probactrosaurus (meaning "before Bactrosaurus") is an early herbivorous hadrosauroid iguanodont dinosaur. It lived in China during the Early Cretaceous period.
Discovery and species

Mounted fossil.

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]
Size Comparison
Life reconstruction

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]

Probactrosaurus was originally assigned by Rozhdestvenky to the Iguanodontidae.[1] Today it is seen as a basal member of the Hadrosauroidea, relatively closely related to the Hadrosauromorpha.[7]
See also
Wikimedia Commons has media related to Probactrosaurus.

Timeline of hadrosaur research


A.K. Rozhdestvensky (1966). "Novyye iguanodonty iz Tsentral'noy Azii. Filogeneticheskiye i taksonomicheskiye v zaimootnosheniya pozdnikh Iguanodontidae i rannikh Hadrosauridae. [New iguanodonts from Central Asia. Phylogenetic and taxonomic interrelationships of late Iguanodontidae and early Hadrosauridae]". Paleontologicheskii Zhurnal. 3: 103–116.
David Norman (2002). "On Asian ornithopods (Dinosauria: Ornithischia). 4. Probactrosaurus Rozhdestvensky, 1966". Zoological Journal of the Linnean Society. 136 (1): 113–144. doi:10.1046/j.1096-3642.2002.00027.x.
J. Lü (1997). "A new Iguanodontidae (Probactrosaurus mazongshanensis sp. nov.) from Mazongshan area, Gansu Province, China". Sino-Japanese Silk Road Dinosaur Expedition. China Ocean Press, Beijing: 27–47.
You, H.-I.; Li, D.-Q.; Dodson, P. (2014). "Gongpoquansaurus mazongshanensis (Lü, 1997) comb. nov. (Ornithischia: Hadrosauroidea) from the Early Cretaceous of Gansu Province, Northwestern China". In Eberth, David A.; Evans, David C. (eds.). Hadrosaurs. Indiana University Press. pp. 73–76. ISBN 978-0-253-01390-3.
Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 292
Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 145. ISBN 978-1-84028-152-1.
Norman, D.B. (2014). "On the history, osteology, and systematic position of the Wealden (Hastings group) dinosaur Hypselospinus fittoni (Iguanodontia: Styracosterna)". Zoological Journal of the Linnean Society. 2014: 1–98. doi:10.1111/zoj.12193.


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