Earliest record of transfer cells in Lower Devonian plants

Area of Science:

• Paleobotany
• Early Terrestrial Ecosystems
• Plant Evolution

Background:

• Early terrestrial ecosystems are reconstructed from fossilized plants and organic encrustations.
• Previous interpretations classified these encrustations as biofilms, biological soil crusts, or lichens.
• A hypothesis suggested some encrustations might represent thalloid gametophytes of embryophytes.

Purpose of the Study:

• To investigate the nature of organic encrustations from early terrestrial ecosystems.
• To test the hypothesis that some encrustations are fossilized thalloid gametophytes of embryophytes.
• To identify the earliest geological evidence of transfer cells (TCs).

Main Methods:

• Extraction of fossils preserved in charcoal from Devonian sediments (Shropshire, UK).
• Scanning electron microscopy (SEM) of fossil specimens.
• Comparison of fossil SEMs with SEMs of extant bryophytes and tracheophytes.
• Transmission electron microscopy (TEM) of a selected fossil specimen.

Main Results:

• Fossils exhibited thalloid and axial morphologies.
• Cells with labyrinthine ingrowths, identified as transfer cells (TCs), were prevalent in the fossils.
• These TCs represent the earliest geological evidence of their kind.
• The findings suggest some organic encrustations are fossilized thalloid land plants, possibly eophytes.

Conclusions:

• The study provides the oldest geological evidence of transfer cells (TCs).
• Organic encrustations can be the remains of thalloid land plants, specifically embryophytes.
• These findings contribute to understanding early plant life and the evolution of terrestrial ecosystems.