Abstract Detail



Paleobotany

Crepet, William [1], Niklas, Karl [2].

The Evolution of Early Vascular Plant Complexity.

The concept of biological complexity is deeply embedded in evolutionary theory and empirical enquiry. Yet, it is largely used intuitively and rarely quantified. Here, using an updated version of our previous phylogenetic analysis of 36 early Paleozoic tracheophytes and the extant genus Equisetum, we discuss the character states of the consensus tree topology and the first appearance of derived character states in a preliminary attempt to quantify the tempo and mode of complexity during a critical evolutionary period in land plant history. Thirty-seven of the best preserved fossil taxa were selected (predominantly from the Silurian–Devonian time interval) to provide as many characters as possible to reduce the negative effects of missing characters in phylogenetic analyses and to most accurately represent phenotypic diversity. In addition, one extant taxon (Equisetum) was added to evaluate its phylogenetic position and effect on the consensus trees. Based on the best preserved taxa representative of their respective lineages, the consensus tree juxtaposed with the first recorded appearance of the fossil taxa showed that anatomical, morphological, and reproductive complexity increased throughout the time interval and that this trend was attended by increasing size within a well-defined zosterophyllophyte-lycophyte clade and a well-defined trimerophyte-euphyllophyte clade. The data indicate that (1) the taxa sampled segregate into two major tracheophyte “superclades” (i.e., a trimerophyte-euphyllophyte clade and a zosterophyllophyte-lycophyte clade), (2) complexity (computed on the basis of emergent character states) and body size increased within each of the two clades, albeit at different tempi, and (3) substantial convergence occurred (e.g., leaves, vascular cambia, roots, and aggregated reproductive structures).


1 - Cornell University, Plant Biology Section, 408 Mann Library, Ithaca, NY, 14853, United States
2 - School Of Integrative Plant Biology, Cornell University, Plant Biology Section, 412 Mann Library, Ithaca, NY, 14853, United States

Keywords:
evolution of complexity
Siolurian-Devonian
vascular plants.

Presentation Type: Oral Paper
Number: 0006
Abstract ID:871
Candidate for Awards:None


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