Research 30 (2009) 239–252

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Cretaceous Research

journal homepage: www.elsevier.com/locate/CretRes

Albertonykus borealis, a new alvarezsaur (Dinosauria: ) from the Early Maastrichtian of Alberta, Canada: implications for the systematics and ecology of the

Nicholas R. Longrich a,*, Philip J. Currie b a Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada b Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada article info abstract

Article history: A new alvarezsaur, Albertonykus borealis, is described from the Lower Maastrichtian of the Horseshoe Received 16 February 2008 Canyon Formation, Alberta, Canada. Forelimb and hindlimb elements from at least two individuals were Accepted in revised form 7 July 2008 recovered from the Albertosaurus bonebed at Dry Island Provincial Park, along with pedal phalanges from Available online 16 July 2008 nearby localities. Phylogenetic analysis shows that Albertonykus is the sister taxon of the Asian clade Mononykinae, consistent with the hypothesis that the alvarezsaurs originated in , and Keywords: then dispersed to Asia via . The discovery of Albertonykus provides important insights into Alvarezsauridae the biology of the Alvarezsauridae. As in other alvarezsaurs, the forelimbs of Albertonykus are specialized Horseshoe Canyon Formation Edmontonian for digging, but they are too short to permit burrowing; they were most likely used to dig into insect Maastrichtian nests. Potential prey items are evaluated in light of the fossil record of social insects. Ants were a minor Isoptera part of the ecosystem during the Cretaceous, and mound-building do not appear until the Alberta Eocene. This leaves the possibility that Albertonykus preyed on wood-nesting termites. We tested this hypothesis by examining silicified wood from the Horseshoe Canyon Formation. It was found that this wood frequently contains borings, which resemble the galleries of dampwood termites (Termopsidae). Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction that these similarities are homoplastic. The basal alvarezsaur , for instance, has a facet on the calcaneum to receive The Alvarezsauridae are small, highly derived theropods known the distal end of the fibula (Novas, 1997), and the basal Con- from the of South America and Laurasia. Alvar- fuciusornis lacks a sternal keel (Chiappe et al., 1999). The Alvar- ezsaurs are characterized by short forelimbs bearing a massive ezsauridae have also been linked to the Ornithomimidae (Martin thumb claw, by elongate hind limbs, and by lightly built skulls with and Rinaldi, 1994; Sereno, 2001) but there is little support for this reduced dentition. This seemingly chimeric morphology has led to hypothesis (Suzuki et al., 2002). Instead, recent phylogenetic a great deal of debate concerning the systematics and ecology of analyses suggest that the alvarezsaurs are basal maniraptorans these strange . (Clark et al., 2002; Novas and Pol, 2002; Turner et al., 2007). At present, there are many hypotheses concerning the origins of The biology of the Alvarezsauridae is no less puzzling. The long, the Alvarezsauridae, but little consensus (Perle et al., 1993, 1994; slender hind limbs of alvarezsaurs indicate that they were highly Wellnhofer, 1994; Zhou, 1995; Novas, 1996, 1997; Sereno, 2001; cursorial. However, the forelimbs are short, robust, and exhibit Clark et al., 2002; Suzuki et al., 2002; Chiappe and Coria, 2003). features typically found in fossorial mammals (Perle et al., 1993), Perle and colleagues (1993, 1994) argued that repre- including a hypertrophied olecranon process, and a robust humerus sented a flightless bird, on the basis of derived characters such as with a distally placed deltopectoral crest. The manus is functionally a distally reduced fibula and a keeled sternum, which are shared monodactylous: the first digit is enlarged and bears a massive claw, with some . A number of phylogenetic analyses supported this whereas the lateral digits are highly reduced (Perle et al., 1993, hypothesis (Novas, 1996, 1997; Forster et al., 1998; Holtz, 1998), but 1994; Suzuki et al., 2002). These features suggest that the hand was the discovery of basal alvarezsaurs and basal avialans has shown designed to tear through a resistant substrate. Alvarezsaur morphology is, therefore, something of a paradox: the morphology of the forelimbs suggests a fossorial lifestyle, but the arms are too * Corresponding author. short, and the hindlimbs too long, for alvarezsaurs to have bur- E-mail address: [email protected] (N.R. Longrich). rowed using the forelimbs (Perle et al., 1994; Novas, 1996). A more

0195-6671/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.cretres.2008.07.005 240 N.R. Longrich, P.J. Currie / Cretaceous Research 30 (2009) 239–252 likely possibility is that alvarezsaurs used their specialized fore- limbs to tear open insect nests (Longrich, 2000; Senter, 2005). The earliest and most primitive alvarezsaurs come from the Late Cretaceous of Patagonia, Argentina; these are calvoi (Bonaparte, 1991), Achillesaurus manazzonei (Martinelli and Vera, 2007) and Patagonykus puertai (Novas, 1996, 1997). The most derived forms are from the Late Cretaceous of Mongolia. These include Mononykus olecranus (Perle et al., 1993, 1994) from the , Parvicursor remotus (Karhu and Rautian, 1996) from the , and deserti (Chiappe et al., 1998, 2002) from the Djadokhta Formation. Although an isolated fibula from the Late Cretaceous of Iren Dabasu, Inner Mongolia, was referred to the Alvarezsauridae by Chiappe et al. Fig. 1. Right: localities of North American alvarezsaur fossils. 1, Albertonykus borealis, Lower Maastrichtian Horseshoe Canyon Formation, Dry Island Provincial Park, Alberta; (2002) it more closely resembles the fibula of Avimimidae, which 2, UCMP 154584, Upper Maastrichtian Hell Creek Formation, Montana; 3, YPM 1049, are common at this locality (N.R.L., pers. obs.). Another putative Upper Maastrichtian Lance Formation, Wyoming. Left: Location of Dry Island Buffalo alvarezsaur is andrewsi, named on the basis of Jump, Alberta. a partial tibiotarsus from the Maastrichtian of Romania (Naish and Dyke, 2004); however, it is not certain that this specimen represents an alvarezsaur, and it could conceivably come from an Gauthier, 1986 oviraptorosaur. Holtz et al. (2004) suggested that Rapator ornitho- lestoides may represent an alvarezsaur, but there is little evidence to Alvarezsauridae Bonaparte, 1991 support such an identification. Until now, only isolated alvarezsaur bones have been described Albertonykus new genus from North America. These include YPM 1049, a third metatarsal from the Upper Maastrichtian Lance Formation of Wyoming (Holtz, Type . Albertonykus borealis new species 1994), and UCMP 154584, a pubis from the coeval Hell Creek Formation of Montana (Hutchinson and Chiappe, 1998). Here, we Derivation of name. The genus name derives from Alberta report on an alvarezsaur from the Lower Maastrichtian of the (province of origin), and onyx (Greek), claw. Horseshoe Canyon Formation of Alberta. It is the earliest known North American alvarezsaur, and its discovery provides important Diagnosis. Small alvarezsaur with the following combination of insights into the systematics and ecology of the Alvarezsauridae. characters: ulna extremely broad (35% as wide as long), bearing

2. Geological setting

Albertonykus was found in south-central Alberta (Fig. 1), in the upper beds of the Horseshoe Canyon Formation. The Horseshoe Canyon Formation consists of sandstones, mudstones, and coals laid down in fluvial and estuarine settings (Lerbekmo and Braman, 2002; Brinkman, 2003; Wu et al., 2007) during Late to Early Maastrichtian times (Edmontonian Land Mammal Age) (Fig. 2). At this time, the area was at roughly 60 North latitude, and bordered the Western Interior Seaway. A moderately diverse assemblage is found in the Horseshoe Canyon Formation (Ryan et al., 1998; Ryan and Russell, 2001) but ectotherms exhibit low diversity in the formation, particularly in the upper half of the formation where Albertonykus was found. The paleoenvironment is thought to have been relatively cool and wet during the Late Campanian, and colder during the Early Maastrichtian, as indicated by the near absence of turtles at this time (Brinkman, 2003).

3. Systematic paleontology

Institutional Abbreviations. MPC, Paleontological Center of the Mongolian Academy of Sciences, Ulaan Baatar; PVPH, Paleontologı´a de Vertebrados, Museo Municipal ‘‘Carmen Funes’’, Plaza Huincul; TMP, Royal Tyrrell Museum of Palaeontology, Drumheller; UALVP, University of Alberta Laboratory for Vertebrate Palaeontology, Edmonton; UCMP, University of California Museum of Paleontology, Berkeley; YPM, Yale Peabody Museum, New Haven.

Dinosauria Owen, 1842

Saurischia Seeley, 1888 Fig. 2. Stratigraphic chart of southern Alberta, showing the stratigraphic position of Theropoda Marsh, 1881 Albertonykus borealis. Stratigraphy after Williamson and Carr (2002). Download English Version: https://daneshyari.com/en/article/4747626

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