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Tyrannosaurids-the familiar group of carnivorous dinosaurs including Tyrannosaurus and Albertosaurus-were the apex predators in continental ecosystems in Asia and North America during the latest Cretaceous (ca. 80-66 million years ago). Their colossal sizes and keen senses are considered key to their evolutionary and ecological success, but little is known about how these features developed as tyrannosaurids evolved from smaller basal tyrannosauroids that first appeared in the fossil record in the Middle Jurassic (ca. 170 million years ago). This is largely because of a frustrating 20+ millionyear gap in the mid-Cretaceous fossil record, when tyrannosauroids transitioned from small-bodied hunters to gigantic apex predators but from which no diagnostic specimens are known. We describe the first distinct tyrannosauroid species from this gap, based on a highly derived braincase and a variety of other skeletal elements from the Turonian (ca. 90-92 million years ago) of Uzbekistan. This taxon is phylogenetically intermediate between the oldest basal tyrannosauroids and the latest Cretaceous forms. It had yet to develop the giant size and extensive cranial pneumaticity of T. rex and kin but does possess the highly derived brain and inner ear characteristic of the latest Cretaceous species. Tyrannosauroids apparently developed huge size rapidly during the latest Cretaceous, and their success in the top predator role may have been enabled by their brain and keen senses that first evolved at smaller body size.dinosaur | Tyrannosauroidea | Uzbekistan | phylogenetics | evolution

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Sulestes karakshi ( = Deltatheroides kizylkumensis Nessov, 1993 = Marsasia aenigma Nessov, 1997 from the Late Cretaceous (Turonian) Bissekty local fauna, Kyzylkum Desert, Uzbekistan, is revised based on additional material from the type locality. It is characterized by an absence of palatal vacuities, double-rooted P1, an asymmetrical M3 with reduced metastylar lobe, an unreduced M4 and m4, obliquely oriented p1, anterior wall of the upper canine alveolus formed by premaxilla, and Meckelian groove on the dentary. PAUP analyses using a data matrix modified from Rougier et al. (1998, 2004) places Sulestes within Deltatheridiidae in an unresolved trichotomy with the Mongolian Campanian Deltatheridium and Deltatheroides. Oklatheridium from the Early Cretaceous of North America is sister taxon to these Late Cretaceous Asiatic deltatheridiidans. Deltatheridiidae is the sister group to other Metatheria including the crown clade Marsupialia. A Deltatheroides-like taxon from the Maastrichtian at Guriliin Tsav, Mongolia, is not related to the Stagodontidae but is sister taxon to other Boreometatheria. The North American Early Cretaceous Atokatheridium, Pappotherium, and Montanalestes are stem tribosphenic mammals, while Holoclemensia is at the base of the eutherian lineage.