1,101 research outputs found
Biometry of Upper Cretaceous (Cenomanian-Maastrichtian) coccoliths - a record of long-term stability and interspecies size shifts
Biometric measurements of Mesozoic coccoliths (coccolith length and width) have been used in short-term biostratigraphic, taxonomic and palaeoecologic studies, but until now, not over longer time scales. Here, we present a long time-series study (⌠30 million years) for the Upper Cretaceous, which aims to identify broad trends in coccolith size and to understand the factors governing coccolith size change over long time scales. We have generated biometric data for the dominant Upper Cretaceous coccolith groups, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa and Watznaueria, from 36 CenomanianâMaastrichtian (100.5â66 Ma) samples from Goban Spur in the northeast Atlantic (DSDP Site 549). These data show that the coccolith sizes within Prediscosphaera, Retecapsa and Watznaueria were relatively stable through the Late Cretaceous, with mean size variation less than 0.7 ÎŒm. Within the Broinsonia/Arkhangelskiella group there was more pronounced variation, with a mean size increase from ⌠6 ÎŒm in the Cenomanian to ⌠10 ÎŒm in the Campanian. This significant change in mean size was largely driven by evolutionary turnover (species origination and extinctions), and, in particular, the appearance of larger species/subspecies (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) in the early Campanian, replacing smaller species, such as Broinsonia signata and Broinsonia enormis. Shorter-term size fluctuations within Broinsonia/Arkhangelskiella, observed across the Late CenomanianâTuronian and Late CampanianâMaastrichtian intervals, may, however, reflect changing palaeoenvironmental conditions, such as sea surface temperature and nutrient availability. / Les dimensions des coccolithes du MĂ©sozoĂŻque (longueur et largeur) ont Ă©tĂ© utilisĂ©es dans des Ă©tudes biostratigraphiques, taxonomiques et palĂ©oĂ©cologiques sur le court-terme mais jusquâĂ prĂ©sent, jamais sur le long-terme. Ici, nous prĂ©sentons lâĂ©tude dâune sĂ©rie chronologique Ă Ă©chelle de temps longue (⌠30 millions dâannĂ©es) du CrĂ©tacĂ© supĂ©rieur, visant Ă identifier les tendances gĂ©nĂ©rales de leur taille et de comprendre les facteurs gouvernant les changements de taille des coccolithes sur une Ă©chelle de temps longue. Nous avons gĂ©nĂ©rĂ© des donnĂ©es biomĂ©triques pour les groupes de coccolithes dominants au CrĂ©tacĂ© supĂ©rieur, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa et Watznaueria, sur 36 Ă©chantillons du CĂ©nomanienâMaastrichtien (100,5â66 Ma) provenant du Goban Spur dans lâAtlantique Nord-Est (DSDP Site 549). Ces donnĂ©es montrent que la taille des coccolithes appartenant aux groupes Prediscosphaera, Retecapsa et Watznaueria fut relativement stable durant tout le CrĂ©tacĂ© supĂ©rieur, avec une variation de la taille moyenne infĂ©rieure Ă 0,7 ÎŒm. Au sein du groupe Broinsonia/Arkhangelskiella, les variations furent plus prononcĂ©es, avec une augmentation de la taille moyenne de ⌠6 ÎŒm au CĂ©nomanien jusquâĂ âŒ 10 ÎŒm au Campanien. Ce changement significatif de la taille moyenne fut largement dĂ» aux processus Ă©volutifs (spĂ©ciations et extinctions), et en particulier Ă lâapparition dâespĂšces/sous-espĂšces plus larges (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) au Campanien infĂ©rieur, remplaçant des espĂšces plus petites, telles que Broinsonia signata et Broinsonia enormis. Cependant, les fluctuations Ă court-terme au sein du groupe Broinsonia/Arkhangelskiella, observĂ©es aux transitions CĂ©nomanienâTuronien et CampanienâMaastrichtien, pourraient reflĂ©ter un changement des conditions palĂ©oenvironnementales, telles que la tempĂ©rature superficielle des eaux ocĂ©aniques et la disponibilitĂ© en nutriment
Identifying prognostic structural features in tissue sections of colon cancer patients using point pattern analysis
Diagnosis and prognosis of cancer is informed by the architecture inherent in cancer patient tissue sections. This architecture is typically identified by pathologists, yet advances in computational image analysis facilitate quantitative assessment of this structure. In this article we develop a spatial point process approach in order to describe patterns in cell distribution within tissue samples taken from colorectal cancer (CRC) patients. In particular, our approach is centered on the Palm intensity function. This leads to taking an approximate-likelihood technique in fitting point processes models. We consider two Neyman-Scott point processes and a void process, fitting these point process models to the CRC patient data. We find that the parameter estimates of these models may be used to quantify the spatial arrangement of cells. Importantly, we observe characteristic differences in the spatial arrangement of cells between patients who died from CRC and those alive at follow-up
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