New stem-lineage representatives of Zatheria (Mammalia) from the Late Jurassic of Portugal

Abstract

ABSTRACT Nanolestes drescherae, new genus and species, a stem-lineage representative of Zatheria, is represented by 48 isolated teeth, a dentary with p2 only, and an anterior dentary fragment with p3–p5 from the Kimmeridgian of the Guimarota coal mine, Portugal. Lower molars of N. drescherae have an enlarged, unicuspid talonid and a small additional cuspule on the cristid obliqua not referable to any of the standard talonid cusps. No trace of an incipient talonid basin is present. Tooth formula is I?/4, C?/1, P?/5, M?/5; all lower teeth except for incisors and m5 are double-rooted. The dentary has a well developed angular process, an internal groove extending beyond m3, and a mandibular foramen in an anterior position. Upper molars have a comparatively large stylocone; cusp “C” is present, stylar cusps are well developed, and additional cusps on the paracrista are present. The former attribution of these specimens to the peramurids cannot be corroborated. The “Porto Pinheiro Molar” from the latest Jurassic/earliest Cretaceous of Porto Pinheiro (or Dinheiro) is referred to Nanolestes as N. krusati, new species. There are no autapomorphies for Arguimuridae Dashzeveg, 1994. The teeth preserved in the holotype of Arguitherium cromptoni Daszheveg, 1994 are p3–p5 and not p4–m1 as assumed in the original description. The teeth described as upper molars of the symmetrodont Thereuodon Sigogneau-Russell, 1989 are posterior upper deciduous premolars (DP?3–5) of holotherians (probably zatherians).