Ronald S Tykoski

Perot Museum of Nature and Science · Paleontology

As a key tool for understanding how animals lived in the past, paleopathology informs us about the lives and deaths of fossil animals. We identify paleopathologies within an assemblage of bones of the pachyrostran centrosaurine Pachyrhinosaurus perotorum, an Arctic ceratopsian. More than 1,000 bones of this dinosaur were collected from the Prince C...

Compared to the osteological record of herbivorous dinosaurs from the Late Cretaceous Prince Creek Formation of northern Alaska, there are relatively fewer remains of theropods. The theropod record from this unit is mostly comprised of isolated teeth, and the only non-dental remains known can be attributed to the troodontid cf. Troodon and the tyra...

Hadrosaurid fossils from the Liscomb Bonebed (Prince Creek Formation, North Slope, Alaska) were the first dinosaur bones discovered from the Arctic. While the Prince Creek Formation hadrosaurids were long identified as Edmontosaurus, a member of the sub-clade Hadrosaurinae, they were recently assigned to a newly-erected taxon, Ugrunaaluk kuukpikens...

While there are now numerous records of dinosaurs from Cretaceous rocks around the state of Alaska, very few fossil records of terrestrial vertebrates are known from the Mesozoic rocks of the southwestern part of the state. Here we report the new discovery of extensive occurrences of dinosaur tracks from Aniakchak National Monument of the Alaska Pe...

The Prince Creek Formation of Alaska, a rock unit that represents lower coastal plain and delta deposits, is one of the most important formations in the world for understanding vertebrate ecology in the Arctic during the Cretaceous. Here we report on an isolated cranial material, supraoccipital, of a lambeosaurine hadrosaurid from the Liscomb Boneb...

The pachyrostran centrosaurine dinosaur Pachyrhinosaurus perotorum is the geologically youngest (Maastrichtian, 70–68.5 Ma) centrosaurine, and latitudinally highest distributed ceratopsid yet known. Continued preparation of material collected from the type locality, the Kikak-Tegoseak Quarry, has produced more examples of cranial material from mult...

We report details of a unique association of hadrosaur and therizinosaur tracks found in the Late Cretaceous lower Cantwell Formation, Denali National Park, central Alaska Range, Alaska. This rock unit is now well-documented as a source of thousands of fossil footprints of vertebrates such as fishes, pterosaurs, and avialan and non-avialan dinosaur...

We report on a paired set of manus and pes tracks from the lower part of the Upper Cretaceous Cantwell Formation in Denali National Park, Alaska, USA. The tridactyl track is bi-lobed in the 'heel' and the morphology allows attribution to a hadrosaurid. While adult hadrosaurs typically reached body lengths of 1200 cm, the length of this Alaskan pes...

The sauropod dinosaur Alamosaurus sanjuanensis Gilmore, 1922 has been known from Maastrichtian deposits of south-western North America for nearly a century. Alamosaurus is the youngest sauropod taxon known in North America. Originally described from an isolated scapula and ischium from New Mexico, more of Alamosaurus was revealed by an incomplete s...

Tyrannosaurid theropods were dominant terrestrial predators in Asia and western North America during the last of the Cretaceous. The known diversity of the group has dramatically increased in recent years with new finds, but overall understanding of tyrannosaurid ecology and evolution is based almost entirely on fossils from latitudes at or below s...

A new specimen attributable to an immature individual of Pachyrhinosaurus perotorum (Dinosauria, Ceratopsidae) from the Kikak-Tegoseak Quarry in northern Alaska preserves a mix of features that provides refinement to the sequence of ontogenetic stages and transformations inferred for the development of the nasal boss in Pachyrhinosaurus. The new sp...

2012. A new Maastrichtian species of the centrosaurine ceratopsid Pachyrhinosaurus from the North Slope of Alaska. Acta Palaeontologica Polonica 57 (3): 561–573. The Cretaceous rocks of the Prince Creek Formation contain the richest record of polar dinosaurs found anywhere in the world. Here we describe a new species of horned dinosaur, Pachyrhinos...

The centrosaurine ceratopsid taxon Pachyrhinosaurus is the most speciose of centrosaurines, being represented by at least three species (P. canadensis, P. lakustai, and the recently described P. perotorum) from the late Campanian and early Maastrichtian of North America. The species are readily distinguished from one another by details of easily vi...

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Two partial theropod braincases recovered from the Upper Cretaceous Prince Creek Formation confirm the presence of Troodon formosus in Alaska. Characters that distinguish one specimen as Troodon formosus include; a very strongly developed sagittal crest on fused parietals, details of pneumatic spaces within the skull bones, and the size and locatio...

We report the occurrence of a furcula (fused clavicles) in both species of the Early Jurassic coelophysid theropod dinosaur Syntarsus (Coelophysidae sensu Holtz, 1994; Coelo-physis and Syntarsus and all descendants of their most recent common ancestor). The furcula is a median pectoral element formed by ontogenetic fusion of the left and right clav...

The fossil record of abelisauroid carnivorous dinosaurs was previously restricted to Cretaceous sediments of Gondwana and probably Europe. The discovery of an incomplete specimen of a new basal abelisauroid, Berberosaurus liassicus, gen. et sp. nov., is reported from the late Early Jurassic of Moroccan High Atlas Mountains. Phylogenetic analysis re...

The fossil record of abelisauroid carnivorous dinosaurs was previously restricted to Cretaceous sediments of Gondwana and probably Europe. The discovery of an incomplete specimen of a new basal abelisauroid, Berberosaurus liassicus, gen. et sp. nov., is reported from the late Early Jurassic of Moroccan High Atlas Mountains. Phylogenetic analysis re...

Not available Geological Sciences

Ceratosauria represents the first widespread and diverse radiation of theropod dinosaurs comprising two main sister clades, Neoceratosauria and Coelophysoidea. This chapter discusses the diagnostic features, phylogenetic placement, and paleobiology of ceratosaurians. The fossil record for Ceratosauria spans a minimum of 155 million years, from the...

We describe a new fossil crocodyliform archosaur from the Early Jurassic Kayenta Formation of the Navajo Nation that is surprisingly derived for so ancient a specimen. High-resolution X-ray CT analysis reveals that its long snout houses an extensive system of pneumatic paranasal cavities. These are among the most distinctive features of modern croc...

Thesis (M.A.)--University of Texas at Austin, 1998. Includes bibliographical references.