Wednesday, October 29, 2014

[Paleontology • 2014] Zaraapelta nomadis • The Ankylosaurid Dinosaurs of the Upper Cretaceous Baruungoyot and Nemegt formations of Mongolia

Life restoration of Zaraapelta nomadis
Illustration: Danielle Dufault | DOI: 10.1111/zoj.12185

The discovery of a new ankylosaurid skull with some unusual features from the Baruungoyot Formation of Mongolia prompted a systematic review of ankylosaurid specimens from the Baruungoyot and Nemegt formations. Dyoplosaurus giganteus was found to possess no diagnostic features and is regarded as a nomen dubium. The holotype of Tarchia kielanae (previously synonymized with Tarchia gigantea) has one autapomorphy, an accessory postorbital ossification with surrounding furrow, and Tar. kielanae is here considered a valid species, making the combination Tar. gigantea unnecessary. An accessory postorbital ossification is also found in the holotype of Minotaurasaurus ramachandrani, and this species is here considered a junior synonym of Tar. kielanae. The newly described skull from the Baruungoyot Formation forms the holotype of a new genus and species, Zaraapelta nomadis gen. et sp. nov., diagnosed by unusual bilayered ornamentation on the squamosal horn and extensive postocular ornamentation. Two distinct tail club handle morphotypes are present in the Nemegt Formation and probably represent two different species. However, it is impossible to assign either tail club morphotype to the single valid species from the formation, Saichania chulsanensis, because of a lack of overlapping material. A revised phylogenetic analysis including newly identified characters found Zaraapelta nomadis to be most closely related to Tar. kielanae.  

Keywords: Ankylosauria; Ankylosauridae; Campanian; Dinosauria; Gobi Desert; Maastrichtian

skull of Zaraapelta nomadis.
photo: Jessica Tansey

Zaraapelta nomadis gen. et sp. nov.
Holotype: MPC D100/1338, a partial skull missing the rostrum.

Etymology: Zaraapelta nomadisзараа (Mongolian) hedgehog, in reference to the spiky appearance of the skull, and pelta (Latin), a small shield, in reference to the osteoderms found on all ankylosaurs; nomadis, from nomas (Latin), nomad, in reference to Mongolian travel company Nomadic Expeditions, which has facilitated many years of palaeontological fieldwork in the Gobi Desert.

Holotype locality and horizon: 43°28.345′N, 99°51.032′E (WGS 84), Hermiin Tsav, Gobi Desert, Mongolia; Baruungoyot Formation (Mid−Upper Campanian, Jerzykiewicz, 2000).

Diagnosis: Ankylosaurine ankylosaurid with bulbous cranial ornamentation. Unlike other ankylosaurs, squamosal horn has unique smooth-textured keel offset from the rest of the squamosal horn by a distinct and abrupt change to a granular texture; elaborate pattern of postocular caputegulae covering entire postocular region between squamosal and quadratojugal horns, with more postocular caputegulae than Ano. lambei, Sa. chulsanensis, or Tar. kielanae.

Victoria M. Arbour, Philip J. Currie and Demchig Badamgarav. 2014. The Ankylosaurid Dinosaurs of the Upper Cretaceous Baruungoyot and Nemegt formations of Mongolia. Zoological Journal of the Linnean Society. 

 Mongolian armoured dinosaur with spiky helmet shows Gobi Desert was hotspot for ankylosaur diversity.