Archaeoceratops

MAKOVICKY, PETER J & NORELL, MARK A, 2006, Yamaceratops dorngobiensis, a New Primitive Ceratopsian (Dinosauria: Ornithischia) from the Cretaceous of Mongolia, American Museum Novitates 3530 (1), pp. 1-44 : 1-2

In spite of an implied ghost lineage for most of the Early and early Late Cretaceous, unquestionable neoceratopsian fossils were unknown for this period until the recent discovery of Archaeoceratops from the Late

Albian of China ( Dong and Azuma, 1997). Since then, several new Early Cretaceous neoceratopsian specimens have been reported, including the basal form Liaoceratops (Xu et al., 2002) and an enigmatic basal taxon

1 Department of Geology, The Field Museum, 1400 S. Lake Shore Drive, Chicago IL 60605 (pmakovicky@ fieldmuseum.org).

2 Division of Paleontology, American Museum of Natural History ([e-mail]).

Chaoyangsaurus (Zhao et al., 1999) based on a holotype that was found several decades ago, but remained undescribed until recently. Cladistic analyses by Sereno (1999, 2000), You and Dodson (2003), and Chinnery (2004) found Chaoyangsaurus to be a neoceratopsian, but the systematic position of this taxon has been contested, and Makovicky (2001) and Xu et al. (2002) posited this taxon to lie outside of the neoceratopsian–psittacosaurid clade. The age of Chaoyangsaurus has also been the subject of debate. Whereas Zhao et al. (1999) attributed a Middle to Late Jurassic age for the Tuchengzhi Formation from which the holotype derives, more recent radiometric dates from near the top of that formation yielded a date of 139 MYA ( Swisher et al., 2002), demonstrating that this formation extends into the earliest Cretaceous. In sum, only two taxa, Liaoceratops and Archaeoceratops , are widely recognized as Early Cretaceous neoceratopsians, in contrast to the 36 or so valid taxa known from the last two stages of the Cretaceous. This disparity belies a still unsampled diversity of taxa at the base of Neoceratopsia .

The 1991 American Museum of Natural History–Mongolian Academy of Sciences (hereafter AMNH-MAS) expedition explored Cretaceous fossil localities in the eastern part of the Gobi Desert, Dorngobi Aimag, Mongolia. A small ceratopsian skull was collected from reddish, poorly consolidated sandstones at the Khugenetslavkant locality. In 2002 and 2003, members of the AMNH- MAS expeditions returned to this locality and collected more ceratopsian material, including a specimen comprising associated skull and skeletal elements. These materials represent a new basal neoceratopsian taxon, which is described here. Where applicable, spelling of Mongolian place names follows Benton (2000) with variant spellings provided in parentheses.

INSTITUTIONAL ABBREVIATIONS

AMNH, American Museum of Natural History, New York; BMNH, The Natural History Museum, London; IGCAGS, Institute of Geology Chinese Academy of Geosciences, Beijing; IGM, Institute of Geology Mongolia, Ulanbaatar; IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing; MOR, Museum of the Rockies, Bozeman; CMN, Canadian Museum of Nature, Ottawa; PIN, Paleontological Institute, Moscow; TsNIGRI, Chernyshev’s Central Museum of Geological Exploration, St. Petersburg; TMP, Royal Tyrrell Museum of Palaeontology, Drumheller; USNM, United States National Museum, Washington DC; ZPAL, Institute of Paleobiology, Polish Academy of Sciences, Warsaw.