1�� School of Environment��Earth and Ecosystem Sciences��Open University��Milton Keynes��MK7 6AA��UK; 2�� Geological Institute����ussian Academy of Sciences��119017 Moscow����ussia; 3�� Claude Bernard University of Lyon 1 and High Normal School of Lyon��Dubois��69622 Villeurbanne Cedex��France; 4�� State Key Laboratory of Systematic and Evolutionary Botany��Institute of Botany��Chinese Academy of Sciences��Beijing 100093��China

The Arctic hosts an extraordinary wealth of terrestrial fossil biotas of Late Cretaceous age representing a diverse and highly productive near-polar ecosystem that has no modern analogue�� Compared to the rest of the Late Cretaceous Maastrichtian plant diversity was at its lowest and the temperature regime the coolest��yet the semi-open forests supported a rich dinosaur fauna made up of a wide range of body sizes and feeding strategies�� The combination of mild winter temperatures and continuous darkness lasting several months imposed severe constraints on primary productivity�� Plant survival strategies involved almost universal winter loss of foliage�� which in turn limited food supply for non-migratory overwintering herbivorous animals�� A combination of leaf form and tree ring studies has been used to quantify year round variations in temperature and determine the tim- ing of spring bud-break and autumnal leaf fall�� While Maastrichtian winter temperatures were cold enough (down to �� 10�� for brief intervals) for frequent frosts and snowfall��summer temperatures were cool but highly variable and at �� 83°N along the north Alaskan coast frequently fell below + 10�� �� Theropod egg shell frag- ments at �� 76°N in the Maastrichtian of Northeastern ��ussia may indicate that dinosaur reproduction took place in the Arctic ecosystem��as distinct from taking place at lower latitude breeding grounds reached by migration�� This raises the question of nest management and specifically the maintenance of incubation temperatures��and the duration of incubation�� Of critical importance to year-round residency is the timing of hatching and juvenile care before winter darkness set in��temperatures fell to near freezing and food resources became limited��