ARTICLE Species composition of the Late Cretaceous eutherian mammal Paranyctoides Fox Marisol Montellano-Ballesteros, Richard C. Fox, and Craig S. Scott Abstract: Although the known record of Mesozoic eutherian mammals has been significantly enriched in recent years, early eutherian evolution is still not well understood. Among the more controversial of Mesozoic eutherians is Paranyctoides Fox, which was described in 1979 from the Judithian Dinosaur Park Formation, Alberta, Canada. It is a rare taxon and therefore has been identified in only a few other North American Late Cretaceous local faunas since. Within the past decade, dental and gnathic remains discovered in Central Asia have also been referred to Paranyctoides, thereby expanding the geographic range of the genus substantially and making it the only Late Cretaceous eutherian ostensibly occurring in both continents. As a result of our detailed study of Paranyctoides, however, we find that the Central Asian species lack the diagnostic characters of Paranyctoides and must be referred to other taxa. We conclude that this genus was limited to North America, ranging from Aquilan to Lancian time, and accordingly we recognize as valid only the following species: Paranyctoides sternbergi (Judithian, Alberta), P. maleficus (Aquilan, Alberta), Paranyctoides Wahweap sp. A and sp. B (Judithian, Utah), Paranyctoides Kaiparowits sp. A and sp. B (Judithian, Utah). Another purported species of Paranyctoides, P. megakeros, from the Lancian of Wyoming, is a junior synonym of Alostera saskatchewanensis. Résumé : Bien que le registre connu des mammifères euthériens du Mésozoïque se soit enrichi considérablement au cours des dernières années, l'évolution précoce des euthériens n'en demeure pas moins mal comprise. L'un des euthériens mésozoïques les plus controversés est Paranyctoides Fox, décrit en 1979 de la Formation d'âge judithien de Dinosaur Park, en Alberta (Canada). Il s'agit d'un taxon rare qui, depuis, n'a été identifié que dans quelques autres assemblages locaux du Crétacé tardif de l'Amérique du Nord. Au cours de la dernière décennie, des restes dentaires et gnathiques découverts en Asie centrale ont également été affectés a ` Paranyctoides, élargissant ainsi considérablement la répartition géographique du genre et en faisant les seuls euthériens du Crétacé tardif possiblement présents sur les deux continents. Il découle toutefois de notre étude détaillée des Paranyctoides que les espèces d'Asie centrale ne présentent pas les caractères diagnostiques de Paranyctoides et doivent donc être affectées a ` d'autres taxons. Nous concluons que ce genre se limitait a ` l'Amérique du Nord, de l'Aquilien au Lancien, et, conséquemment, nous ne reconnaissons que les espèces suivantes comme étant valides : Paranyctoides sternbergi (Judithien, Alberta), P. maleficus (Aquilien, Alberta), Paranyctoides Wahweap sp. A et sp. B (Judithien, Utah), Paranyctoides Kaiparowits sp. A et sp. B (Judithien, Utah). Une autre espèce présumée de Paranyctoides, P. megakeros, du Lancien du Wyoming, est en fait un synonyme junior d'Alostera saskatchewanensis. [Traduit par la Rédaction] Introduction The past few decades have witnessed a significant increase in new information concerning Mesozoic eutherian mammals, based on newly discovered specimens from North America and Eurasia. Although detailed descriptions and hypotheses of rela- tionships of many of these new taxa have been published (e.g., Wible et al. 2009), the early evolution of eutherians is still not well understood. Among these problematic early eutherians is the ge- nus Paranyctoides Fox (1979), initially described from the Judithian NALMA Dinosaur Park Formation (= Oldman Formation of earlier authors; see Eberth 2005 and references therein), Alberta, Canada. It is considered an important taxon for understanding early eutherian evolution because it is one of the oldest unequivo- cally identified member of this group from North America (Kielan-Jaworowska et al. 2004), and its relationships and taxo- nomic position within Eutheria, especially to Cenozoic Eulipo- typhla (McKenna and Bell 1997), are still in dispute. Since its first recognition, several Aquilan, Judithian, and Lancian North American species of Paranyctoides have been described (e.g., Fox 1984; Lillegraven and McKenna 1986; Cifelli 1990). More surprising is the purported recognition of Paranyctoides in the late Turonian–Coniacian faunas of Uzbekistan, Central Asia (e.g., Nessov 1993; Archibald and Averianov 2001; Averianov and Archibald 2003, 2013), making it the only genus of Mesozoic eutherians to occur in both North America and Eurasia. Indeed, the only family level taxon of Cretaceous tribotherians otherwise known to occur in both North American and Eurasia is the Deltatheridiidae (Fox 1974), animals that may be stem Metatheria (Rougier et al. 1998). The unique geographical distribution of Paranyctoides among all eutherians has led us to review critically the material that has been identified as or referred to Paranyctoides to understand better the fundamental aspects of its evolutionary history. Institutional abbreviations AMNH American Museum of Natural History, New York; CCMGE, Chernyshev=s Central Museum of Geological Exploration, Saint Petersburg; MNA, Museum of Northern Arizona, Flagstaff; OMNH, Oklahoma Museum of Natural History, Norman; TMP, Received 10 December 2012. Accepted 12 March 2013. Paper handled by Associate Editor Hans Sues. M. Montellano-Ballesteros. Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Cd Universitaria, Delegación Coyoacán, México, D.F. 04510, Mexico. R.C. Fox. Laboratory for Vertebrate Paleontology, Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada. C.S. Scott. Royal Tyrrell Museum of Palaeontology, P.O. Box 7500, Drumheller, AB T0J 0Y0, Canada. Corresponding author: Marisol Montellano-Ballesteros (e-mail: marmont@unam.mx). 693 Can. J. Earth Sci. 50: 693–700 (2013) dx.doi.org/10.1139/cjes-2012-0184 Published at www.nrcresearchpress.com/cjes on 19 March 2013. 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