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The Late Cretaceous of Western North America (Laramidia) supported a diverse dinosaur fauna, with duckbilled dinosaurs (Hadrosauridae) being among the most speciose and abundant members of this assemblage. Historically, collecting and preservational biases have meant that dinosaurs from Mexico and the American Southwest are poorly known compared to those of the northern Great Plains. However, evidence increasingly suggests that distinct species and clades inhabited southern Laramidia. Here, a new kritosaurin hadrosaurid, represented by the anterior part of a skull, is reported from the late Campanian of the Cerro del Pueblo Formation, ~72.5 Ma, in Coahuila, Mexico. The Cerro del Pueblo Formation kritosaur was originally considered to represent the same species as a saurolophine from the Olmos Formation of Sabinas, but the Sabinas hadrosaur is now considered a distinct taxon. More recently, the Cerro del Pueblo Formation kritosaur has been referred to Kritosaurus navajovius. We show it represents a new species related to Gryposaurus. The new species is distinguished by its large size, the shape of the premaxillary nasal process, the strongly downturned dentary, and massive denticles on the premaxilla's palatal surface, supporting recognition of a new taxon, Coahuilasaurus lipani. The dinosaur assemblage of the Cerro del Pueblo Formation shows higher diversity than the contemporaneous fauna of the Horseshoe Canyon Formation in Alberta. Furthermore, Kritosaurini, Lambeosaurini, and Parasaurolophini all persist into the latest Campanian in southern Laramidia after disappearing from northern Laramidia. These patterns suggest declining herbivore diversity seen at high latitudes may be a local, rather than global phenomenon, perhaps driven by cooling at high latitudes in the Late Campanian and Maastrichtian. [ABSTRACT FROM AUTHOR]

Large, actively swimming suspension feeders evolved several times in Earth's history, arising independently from groups as diverse as sharks, rays and stem teleost fishes (1), and in mysticete whales (2). However, animals occupying this niche have not been identified from the early Palaeozoic era. Anomalocarids, a group of stem arthropods that were the largest nektonic animals of the Cambrian and Ordovician periods, are generally thought to have been apex predators (3-5). Here we describe new material from Tamisiocaris borealis (6), an anomalocarid from the Early Cambrian (Series 2) Sirius Passet Fauna of North Greenland, and propose that its frontal appendage is specialized for suspension feeding. The appendage bears long, slender and equally spaced ventral spines furnished with dense rows of long and fine auxiliary spines. This suggests that T. borealiswas a microphagous suspension feeder, using its appendages for sweep-net capture of food items down to 0.5 mm, within the size range of mesozoo-plankton such as copepods. Our observations demonstrate that large, nektonic suspension feeders first evolved during the Cambrian explosion, as part of an adaptive radiation of anomalocarids. The presence of nektonic suspension feeders in the Early Cambrian, together with evidence for a diverse pelagic community containing phytoplankton (7,8) and mesozooplankton (7,9,10), indicate the existence of a complex pelagic ecosystem (11) supported by high primary productivity and nutrient flux (12,13). Cambrian pelagic ecosystems seem to have been more modern than previously believed., T. borealis, from the Early Cambrian Sirius Passet fauna of North Greenland, has been described previously as a possible anomalocarid on the basis of a disarticulated frontal appendage (6). New [...]

Snakes are the most diverse group of lizards (1), but their origins and early evolution remain poorly understood owing to a lack of transitional forms. Several major issues remain outstanding, [...]