A 3D model of a 400-million-year-old fossil has shed light on an enduring
mystery about how some of Earth's first plants evolved and helped make the
planet liveable.
The model reveals how one of the earliest form of roots developed during the
Early Devonian period, a key era when plants began to spread across land.
The evolution of plants from simple stems to more complex forms with roots
had a dramatic impact on the planet, experts say. Plant roots reduced
atmospheric CO2 levels, stabilized the soil and revolutionized water
circulation across the surfaces of continents.
Digital reconstruction
An international team led by the University of Edinburgh used digital
techniques to produce the first complete 3D reconstruction of Asteroxylon
mackiei, an early ancestor of clubmosses—evergreen herbs with needle-like
leaves that are a key feature of Scottish flora today.
The model allowed scientists to visualize the structure and understand the
root development of this ancient plant, whose fossil was found in the Rhynie
chert—a sedimentary deposit near the Aberdeenshire village of Rhynie, that
holds some of the oldest and best-preserved plant fossils in the world.
Root development
The findings show that the roots of Asteroxylon developed in a fundamentally
different way from contemporary plants.
It grew by a process known as dichotomous branching—where the tip of a leafy
shoot splits to produce two new branches, one a shoot, the other developing
into a root.
In today's plants new roots arise from within growing shoots or roots.
Evolutionary stage
Experts say this discovery shows a hitherto unseen evolutionary stage
between the earliest plants that lacked roots and living clubmosses that
possess them.
The research is published in the journal eLife.
Dr. Sandy Hetherington says that "how plants evolved from simple stems to
complex forms with roots and leafy shoots remains one of the key questions
in plant evolution. First discovered a century ago, the Rhynie chert
continues to provide fossils that change our view of land plant evolution.
Our 3D model of Asteroxylon demonstrates the value of evidence-based
reconstructions for understanding the development and evolution of the first
complex plants on Earth."
"100 years after the discovery of the fossils in Rhynie, our reconstruction
demonstrates what these enigmatic plants really looked like," explains
Professor Liam Dolan. "These are the oldest known structures that resemble
modern roots and now we know how they formed."
"It is remarkable how modern technology has allowed us to visualize the
structure and understand the development of a plant that is more than 400
million years old," concludes Siobhán Bridson of the University of Oxford.
Reference:
Alexander J Hetherington et al, An evidence-based 3D reconstruction of
Asteroxylon mackiei, the most complex plant preserved from the Rhynie chert,
eLife (2021).
DOI: 10.7554/eLife.69447