Description of the first definitive Corythosaurus (Dinosauria, Hadrosauridae) specimens from the Judith River Formation in Montana, USA and their paleobiogeographical significance.

Despite the long history of research in the late Campanian Judith River Formation in northern Montana, most of the vertebrate fossils are represented by fragmentary remains, making precise taxonomic identifications difficult. Contrary to this, the partially contemporaneous Dinosaur Park Formation, Alberta, Canada is known for its tremendous fossil preservation, permitting rigorous studies of dinosaur diversity, evolution, and biostratigraphy. Hadrosaurids comprise one of the most abundant dinosaur clades in the Dinosaur Park Formation, but taxonomic affinities of hadrosaurid specimens remain poorly understood in the Judith River Formation. Corythosaurus is the most common hadrosaurid in the Dinosaur Park Formation and, to date, has been restricted to this formation. This study reports the first definitive Corythosaurus specimens from the Judith River Formation, which were discovered on two private ranches in northern Montana. The attribution of the most complete skeleton to Corythosaurus is indicated by: wide crest-snout angle, presence of premaxilla-nasal fontanelle, dorsoventrally expanded nasal, laterally exposed ophthalmic canal of the laterosphenoid, and tall neural spines. A second specimen preserves a large ilium that can be positively identified as Corythosaurus based on its associated skull, which is now in private hands. The specimens were recovered from the Coal Ridge Member of the Judith River Formation, which is approximately time equivalent to the Dinosaur Park Formation. Thus, the discovery of Corythosaurus in the Judith River Formation extends the biogeographic range of this genus and establishes a framework for future interformational biostratigraphic studies of Late Cretaceous dinosaur faunas in North America.

Scythes, sickles and other blades: defining the diversity of pectoral fin morphotypes in Pachycormiformes.

The traditional terminology of 'scythe' or 'sickle' shaped is observed to be flawed as an effective descriptor for pectoral fin shape in pachycormids. The diversity of pachycormid pectoral fin shapes is assessed across the 14 recognised genera that preserve complete pectoral fins, and improved terms are defined to more effectively describe their form, supported by anatomical observation and aspect ratio analysis of individual fins, and corroborated by landmark analysis. Three clear and distinct pectoral fin structural morphotypes emerge (falceform, gladiform, falcataform), reflecting a diversity of pachycormid lifestyles throughout the Mesozoic, from agile pursuit predator to slow-cruising suspension feeder.

The real Bigfoot: a pes from Wyoming, USA is the largest sauropod pes ever reported and the northern-most occurrence of brachiosaurids in the Upper Jurassic Morrison Formation.

A set of associated left pedal elements of a sauropod dinosaur from the Upper Jurassic Morrison Formation in Weston County, Wyoming, is described here. Several camarasaurids, a nearly complete small brachiosaur, and a small diplodocid have been found at this locality, but none match the exceptionally large size of the pedal elements. Next to the associated pedal elements, an isolated astragalus, phalanx and ungual were found, which match the large metatarsals in size. The elements cannot be ascribed to diplodocids due to the lack of a ventral process of metatarsal I. Moreover, the morphology of metatarsal V has a broad proximal end, with a long and narrow distal shaft, which differs from Camarasaurus. The size of the material and a medially beveled distal articular surface of metatarsal IV imply an identification as a brachiosaurid. This is the largest pes ever reported from a sauropod dinosaur and represents the first confirmed pedal brachiosaur elements from the Late Jurassic of North America. Furthermore, this brachiosaur material (the pes and the small nearly complete specimen) is the northernmost occurrence of brachiosaurids in the Morrison Formation.

100-million-year dynasty of giant planktivorous bony fishes in the Mesozoic seas.

Large-bodied suspension feeders (planktivores), which include the most massive animals to have ever lived, are conspicuously absent from Mesozoic marine environments. The only clear representatives of this trophic guild in the Mesozoic have been an enigmatic and apparently short-lived Jurassic group of extinct pachycormid fishes. Here, we report several new examples of these giant bony fishes from Asia, Europe, and North America. These fossils provide the first detailed anatomical information on this poorly understood clade and extend its range from the lower Middle Jurassic to the end of the Cretaceous, showing that this group persisted for more than 100 million years. Modern large-bodied, planktivorous vertebrates diversified after the extinction of pachycormids at the Cretaceous-Paleogene boundary, which is consistent with an opportunistic refilling of vacated ecospace.