Decoding the dynamics of dental distributions: insights from shark demography and dispersal.

Shark teeth are one of the most abundant vertebrate fossils, and because tooth size generally correlates with body size, their accumulations document the size structure of populations. Understanding how ecological and environmental processes influence size structure, and how this extends to influence these dental distributions, may offer a window into the ecological and environmental dynamics of past and present shark populations. Here, we examine the dental distributions of sand tigers, including extant and extinct , to reconstruct the size structure for a contemporary locality and four Eocene localities.

Nesting at extreme polar latitudes by non-avian dinosaurs.

The unexpected discovery of non-avian dinosaurs from Arctic and Antarctic settings has generated considerable debate about whether they had the capacity to reproduce at high latitudes-especially the larger-bodied, hypothetically migratory taxa. Evidence for dinosaurian polar reproduction remains very rare, particularly for species that lived at the highest paleolatitudes (>75°). Here we report the discovery of perinatal and very young dinosaurs from the highest known paleolatitude for the clade-the Cretaceous Prince Creek Formation (PCF) of northern Alaska.

Using tooth enamel microstructure to identify mammalian fossils at an Eocene Arctic forest.

Lower Eocene (Wasatchian-aged) sediments of the Margaret Formation on Ellesmere Island in Canada's High Arctic preserve evidence of a rainforest inhabited by alligators, turtles, and a diverse mammalian fauna. The mammalian fossils are fragmentary and often poorly preserved. Here, we offer an alternative method for their identification.

The palaeobiology of high latitude birds from the early Eocene greenhouse of Ellesmere Island, Arctic Canada.

Fossils attributable to the extinct waterfowl clade Presbyornithidae and the large flightless Gastornithidae from the early Eocene (~52-53 Ma) of Ellesmere Island, in northernmost Canada are the oldest Cenozoic avian fossils from the Arctic. Except for its slightly larger size, the Arctic presbyornithid humerus is not distinguishable from fossils of Presbyornis pervetus from the western United States, and the Gastornis phalanx is within the known size range of mid-latitude individuals. The occurrence of Presbyornis above the Arctic Circle in the Eocene could be the result of annual migration like that of its living duck and geese relatives, or it may have been a year-round resident similar to some Eocene mammals on Ellesmere and some extant species of sea ducks.

First record of eocene bony fishes and crocodyliforms from Canada's Western Arctic.

Background: Discovery of Eocene non-marine vertebrates, including crocodylians, turtles, bony fishes, and mammals in Canada's High Arctic was a critical paleontological contribution of the last century because it indicated that this region of the Arctic had been mild, temperate, and ice-free during the early - middle Eocene (∼53-50 Ma), despite being well above the Arctic Circle. To date, these discoveries have been restricted to Canada's easternmost Arctic - Ellesmere and Axel Heiberg Islands (Nunavut). Although temporally correlative strata crop out over 1,000 km west, on Canada's westernmost Arctic Island - Banks Island, Northwest Territories - they have been interpreted as predominantly marine.