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Abstract Detail



Paleobotany

Atkinson, Brian A [1].

An integration of fossils, phylogeny, and disparity: Reconstructing the Cretaceous radiation of Cornales.

The order Cornales (605 species) is the earliest diverging lineage within the most diverse core eudicot clade, the asterids (>80,000 species). Paleobotanical studies and molecular divergence time analyses indicate that the order rapidly radiated into its major clades during the Late Cretaceous (100-66 Ma). This initial rapid radiation has made it difficult for molecular phylogenetic analyses to resolve deep-node relationships within Cornales. However, recent paleobotanical studies have begun to shed light on this phylogenetic radiation. Most Cretaceous cornalean fossils are represented by fruits, which contain numerous systematically informative characters for the delineation of major cornalean clades and families. Therefore, cornalean fruits have great potential for elucidating the early evolution of Cornales. In this study, deep-node phylogenetic relationships and early patterns of morphological diversity (disparity) within Cornales are reconstructed. A cladistic matrix consisting of 77 fruit morphological characters and 58 taxa (35 extant, 23 extinct) was assembled. To infer cornalean phylogenetic relationships, the data matrix was analyzed using parsimony. The impact of fossils on phylogenetic inference was assessed by excluding extinct species in a separate analysis. Strict consensus trees (SCT), from both analyses resulted in a monophyletic Cornales with resolved deep-node relationships. However, resolution in the fossil inclusive SCT is substantially higher, revealing a cornalean basal grade including Loasaceae, Hydrangeaceae, Hydrostachyaceae, Grubbiaceae, a Hironoia-Amersinia clade, and Curtisiaceae, respectively, leading to a 'core' clade. The core group contains a clade comprising a grade of Late Cretaceous taxa leading to a clade of Nyssaceae, Mastixiaceae, and Davidiaceae, which is sister to a Cornaceae-Alangiaceae clade. A time-scaled phylogeny using approximate stratigraphic ranges of terminal fossil taxa indicates that the primary diversification of Cornales occurred before the Coniacian (89.8 Ma). Morphospace occupation and disparity of Cornales through time were analyzed using a modified matrix (drupaceous taxa only). The taxa were organized into three time bins: Late Cretaceous (100-66 Ma), Paleogene (66-23.03 Ma), and Neogene-Recent (<23.03 Ma). Morphospace and disparity analyses are concordant, revealing that Cretaceous taxa occupy a significantly different area of morphospace and have significantly lower disparity values than Cenozoic taxa. By the Paleogene, there was a significant shift and expansion in morphospace occupation. Maximum levels of cornalean disparity were reached by the Paleogene and remained relatively constant throughout the Cenozoic. These changes in morphospace occupation and disparity of cornaleans may be due to a combination of whole genome duplication events and ecological responses to major environmental changes.


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1 - University of Kansas, Department of Ecology and Evolutionary Biology, 2041 Haworth Hall, 1200 Sunnyside Avenue , Lawrence, KS, 66045, USA

Keywords:
phylogenetics
Morphological disparity
Cretaceous
Morphospace
Fossils.

Presentation Type: Oral Paper
Number: 17007
Abstract ID:232
Candidate for Awards:None


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