Abstract

Maelestes gobiensis Wible et al., 2007 is the second new eutherian mammal to be discovered at the rich Mongolian Late Cretaceous locality of Ukhaa Tolgod, Ukhaatherium nessovi Novacek et al., 1997, being the first. Maelestes is only the seventh Late Cretaceous eutherian known from the skull and the upper and lower dentitions, and the fifth known from some postcranial elements. The type and only known specimen, PSS-MAE 607, is described and illustrated in detail. The type is amended to include: an incomplete skull, left mandible, atlas, axis, last cervical and first 11 thoracic vertebrae, 11 partial ribs, incomplete scapula, clavicle, humerus, and proximal radius and ulna. An astragalus on a separate block was referred to Maelestes by Wible et al. (2007), but is too large to belong to this taxon and is removed from the isotype.
Several corrections and updates are made to the phylogenetic analysis of Wible et al. (2007). This analysis included 408 morphological characters (127 dental, 212 cranial, and 69 postcranial) in Maelestes along with 68 other taxa (four stem therians, three metatherians, 31 Cretaceous eutherians, 20 extinct Tertiary placentals, and 11 extant placentals). Maelestes is identified as a member of Cimolestidae sensu Kielan-Jaworowska et al. (2004) along with the slightly younger and poorer known North American taxa Batodon Marsh, 1892, and Cimolestes Marsh, 1889. Cimolestidae, in turn, is grouped with Asioryctitheria sensu Archibald and Averianov (2006), which is comprised of monophyletic Mongolian and Uzbekistani clades. The other principal Late Cretaceous clades are: a laurasian Zhelestidae; Paranyctoides Fox, 1979 (North American and Uzbekistan) + Eozhelestes Nessov, 1997 (Uzbekistan); and an Asian Zalambdalestidae. In contrast to several previous analyses, but in common with Wible et al. (2007), no Cretaceous eutherians are identified as members of any placental group.