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Title: Influence of paleogeography, climate and evolution on Cretaceous vegetation biomes
Author: Peralta-Medina, Emiliano
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2013
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The Cretaceous Period was a time of extreme greenhouse warmth and a time of major global events. Hence, the Cretaceous represents an interesting geologic time to study a biota that lived under a very different evolutionary context and climate dynamics compared to the present. This thesis examines the geographic patterns of plant biomes based on a global quantitative analysis of palaeobotanical evidence. The distribution, ecology, and composition of Cretaceous floras are assessed through the analysis of databases built from information found in museums, collections, electronic resources and literature published since the 1800s. Biogeographic analyses of Cretaceous woods reveal that araucarioid and podocarpoid conifers were globally codominant in equatorial regions during Early Cretaceous times while cupressoid conifers were most common in midlatitude. The analysis of pinoid wood reveals these conifers were mainly distributed at high latitudes and exclusively restricted to the Northern Hemisphere since the Cretaceous. Spatial analysis suggests that the loss of conifer forests was linked to the rise of co-occurring angiosperms, which spread and dominated high latitudes until the Late Cretaceous, somewhat latter than indicated by palynological studies. Biogeographic analyses of Cheirolepid conifers show a significant spatial correlation between the distribution of arid climate-sensitive sediments (evaporites and calcrete) and cheirolepid occurrences during the Early Cretaceous. In contrast, Late Cretaceous cheirolepids show a stronger correlation with sediments that indicate humid tropical environments (coal, kaolinite, and bauxite). This finding adds evidence to the fact that the presence of cheirolepid fossil does not exclusively indicate arid environments as previously thought. Biogeographic analyses of Cretaceous plants improve the knowledge of Cretaceous vegetation biomes and allow to investigate possible macroevolutionary patterns over extended spatiotemporal scales, offering a valuable quantitative comparison to integrate with computer climate models proposed for the Cretaceous. Furthermore, two putative Cretaceous woods were examined to clarify their age, provenance and affinity. Results show the valuable use of biogeography, taphonomy, wood anatomy and morphometrics as an essential tool for taxonomic revision of Cretaceous fossil material. An extensive taxonomic re-examination of problematic fossil samples is recommended in order to improve data quality to develop more accurate biome reconstructions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Cretaceous ; Fossil wood ; Biogeography ; Palaeontology