Structural Fingerprints of Development at the Intersection of Evo-Devo and the Fossil Record

Abstract

The plant body preserves diagnostic structural features that develop as the result of specific regulatory genes and growth regulators. When recognized in extinct species, those features serve as structural fingerprints for the regulatory programs by which they were produced.We review the contributions of the fossil record to understanding the evolution of plant development in a temporal (geologic time) and a structural perspective (morphology, anatomy), and we highlight major topics in plant evolution in which integration of data from fossil and living plants has yielded significant resolution. Up to the present, the most ubiquitous growth regulator, auxin, has been documented as essential to the regulation of secondary growth and wood formation not only in seed plants, but also in several other major groups in which living species are no longer characterized by secondary growth. Additional fingerprints of growth regulation reveal the occurrence of gravitropic responses in fossils that extend back in time 400 million years and explain the evolution of equisetacean reproductive morphologies, living and extinct, by the interaction of modular regulatory programs. Still other fingerprints document parallel evolution of stem/leaf organography in several clades of living plants (e.g., ferns, Equisetum, and seed plants) and of substantial rooting systems that facilitated evolution of giant trees in extinct lycophytes and seed plants. Future application of techniques for identifying and interpreting the significance of structural fingerprints to a much broader spectrum of developmental processes holds tremendous potential for the paleontological record to substantially illumi- nate and enhance understanding of systematics and evolution within the context of plant development. Keywords