Gobisaurus

''Gobisaurus'' is an extinct genus of herbivorous basal ankylosaurid ankylosaur from the Lower Cretaceous of China (''Nei Mongol Zizhiqu''). The genus is monotypic, containing only the species ''Gobisaurus domoculus''.

Discovery and naming

The Sino-Soviet Expeditions (1959–1960) discovered an ankylosaurian skeleton in the Gobi Desert of Inner Mongolia near Moartu, in the region of the Alashan Desert. The find was largely neglected until fossils were selected for a travelling exhibition touring the globe between 1990 and 1997, in the context of the China-Canada Dinosaur Project. The postcranial skeleton could not be located but the skull was displayed, informally labelled "Gobisaurus", at the time a ''nomen nudum''.

In 2001, Matthew K. Vickaryous, Anthony P. Russell, Philip John Currie and Zhao Xijin named and described the type species ''Gobisaurus domoculus''. The generic name means "Gobi (Desert) lizard," referring to its provenance. The specific name means "hidden from view" in Latin, referring to its being overlooked for three decades.Matthew K. Vickaryous, Anthony P. Russell, Philip J. Currie, and Xi-Jin Zhao. 2001. "A new ankylosaurid (Dinosauria: Ankylosauria) from the Lower Cretaceous of China, with comments on ankylosaurian relationships". ''Canadian Journal of Earth Sciences''/''Revue canadienne des sciences de la Terre'' 38(12): 1767-1780 http://www.nrcresearchpress.com/doi/pdf/10.1139/e01-051

The holotype, IVPP V12563, was found in a layer of the Miaogou Formation (Maortu locality; originally interpreted as the nearby Ulansuhai Formation). Some studies indicate it may date to the Turonian, but others suggest an older date spanning between the Barremian and Albian. It consists of a skull and the as yet undescribed postcranial remains.

In 2014, Victoria Arbour concluded that '' Zhongyuansaurus'', the type specimen of which, HGM 41HIII-0002, includes extensive postcranial remains, was a possible junior synonym of ''Gobisaurus''.Arbour, Victoria Megan, 2014. ''Systematics, evolution, and biogeography of the ankylosaurid dinosaurs''. Ph.D thesis, University of Alberta

Description

''Gobisaurus'' is a large ankylosaurian. The skull measured in length and across.Vickaryous M.K., Maryańska T., Weishampel D.B., 2004, "Ankylosauria". Chapter 17 in: Weishampel D.B., Dodson P., Osmólska H., editors. ''The Dinosauria''. 2nd ed. Berkeley (CA): University of California Press. p. 363–392

''Gobisaurus domoculus'' shares many cranial similarities with '' Shamosaurus scutatus'', including a rounded squamosal, short squamosal horns, low supraorbital bosses, large elliptical orbital fenestrae and external nares (oval eye sockets and nostrils), the cross-section of the eye sockets being about a fifth of skull length, a deltoid dorsal profile with a narrow rostrum (a narrow, kite-shaped, snout in top view), quadratojugal protuberances (cheek horns), and caudolaterally directed paroccipital processes (extensions of the rear skull pointing to behind and sideways). But the two taxa may be distinguished by differences in the length of the maxillary tooth row (26,6% instead of 40% of total skull length with ''Gobisaurus''), an unfused basipterygoid-pterygoid process in ''Gobisaurus'', the front of the pterygoid being in e vertical position, the presence on an elongate vomerine premaxillary process in ''Gobisaurus'', and the presence of cranial sculpting in ''Shamosaurus'', but not in ''Gobisaurus''. This latter difference was denied by Arbour who concluded that the degree of sculpting was roughly the same.

The external nostrils had about 23% of skull length.

HGM 41HIII-0002, the holotype of ''Zhongyuansaurus'', preserves a tail club "handle": the vertebrae toward the end of the tail interlock tightly, making the end stiff. However, this specimen does not appear to have a tail club "knob", the bulbous osteoderms seen in derived ankylosaurids.

Phylogeny

''Gobisaurus'' was placed in the Ankylosauridae in 2001. Vickaryous et al., 2004 found that a clade formed by ''Shamosaurus'' and ''Gobisaurus'' is "nested deep within the ankylosaurid lineage as the first successive outgroup to (the subfamily) Ankylosaurinae".

Other analyses find a more basal position as the sister species of ''Shamosaurus''. Concluding that ''Zhongyuansaurus'' was a probable junior synonym of ''Gobisaurus'', Arbour considered it unnecessary to use the term Shamosaurinae for the clade including just ''Shamosaurus'' and ''Gobisaurus''.

''Gobisaurus'' in a cladogram simplified from Zheng et al. (2018):

In phylogenetic analyses by Xing et al. (2024), ''Gobisaurus'' is recovered as a member of Shamosaurinae or as an ankylosaurid less derived than ''Shamosaurus''. Below are two simplified cladograms from that study:

Topology A: Zheng et al. (2018) dataset + '' Datai'' (14-taxon deletion)

Topology B: Raven et al. (2023) dataset + '' Datai'' (34-taxon deletion)

See also

* Timeline of ankylosaur research

References

{{Taxonbar, from=Q134952

Ankylosauridae
Dinosaur genera
Early Cretaceous dinosaurs
Fossil taxa described in 2001
Taxa named by Philip J. Currie
Dinosaurs of China