No abstract

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 crocodylians, yet the evolutionary history of this unique system has been obscured by the inaccessibility of internal structures in most fossil crania. Preliminary phylogenetic analysis indicates that the new species is the oldest known member of a monophyletic Goniopholididae, and within this lineage to be the sister taxon of Eutretauranosu-chus, from the Late Jurassic Morrison formation of Colorado. Goniopholididae became extinct at the end of the Cretaceous, but it is more closely related to living crocodylians than are several lineages known only from Cretaceous and younger fossils. The new taxon nearly doubles the known length of goniopholid history and implies a deep, as yet undiscovered, Mesozoic history for several crocodyliform lineages that were once thought to have relatively complete fossil records.

The fossil recorcl of abelisauroiclcarnivorousclinosaurs was previously restricted to Cretaceous secliments of and probably Europe.The of an incompletespecimen of a new basal gen. et sp. nov.. is reported from the late Early Jurassic of Moroccan Atlas Mountains. Phylogenetic analysis recovers Ceratosauroiclea ancl Coelophysoidea as sister lineages within Ceratosauria. and as a basal abelisauroicl. is the oldest known abelisauroiclancl extends the first appearance datum of this lineage by about 50 million years. The temporal. morphological. and phylogenetic gaps that have hitherto separated Triassic to Early Jurassic coelophysoids from Late Jurassic through Cretaceous The discovery of an African abelisauroicl in the Early Jurassic confirms at least a distribution of this group long before the Cretaceous.

No abstract

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 southern Canada and central Asia. Remains of a new, relatively small tyrannosaurine were recovered from the earliest Late Maastrichtian (70-69Ma) of the Prince Creek Formation on Alaska's North Slope. Cladistic analyses show the material represents a new tyrannosaurine species closely related to the highly derived Tarbosaurus+Tyrannosaurus clade. The new taxon inhabited a seasonally extreme high-latitude continental environment on the northernmost edge of Cretaceous North America. The discovery of the new form provides new insights into tyrannosaurid adaptability, and evolution in an ancient greenhouse Arctic.