Digital replica of old microscopic green algae.
WASHINGTON:
Scientists have discovered the oldest fossils of a green plant ever found in rocks from northern China, tiny algae that were carpeted about a billion years ago and were part of an original revolution in life on Earth.
Researchers said Monday that the plant, called Proterocladus antiquus, was about the size of a grain of rice and had numerous thin branches that thrived in shallow water while attached to the sea floor with a root-like structure.
It may seem small, but Proterocladus – a form of green algae – was one of the largest organisms of its time and mainly shared the oceans with bacteria and other microbes. It deals with photosynthesis, converts energy from sunlight into chemical energy and produces oxygen.
"Proterocladus antiquus is a close relative of the ancestor of all green plants living today," said Qing Tang, a post-doctoral researcher at Virginia Tech in paleobiology who discovered the rock fossils excavated in Liaoning province near the city of Dalian and was the lead author in the journal Nature Ecology & Evolution published study.
The Earth's biosphere depends heavily on plants to receive food and oxygen. The first land plants believed to be descendants of green algae appeared around 450 million years ago.
Maybe 2 billion years ago there was an evolutionary shift on Earth from simple bacteria-like cells to the first members of a group called eukaryotes, which includes fungi, plants, and animals. The first plants were unicellular organisms. The transition to multicellular plants such as Proterocladus was a pivotal development that paved the way for the turmoil of the plants that inhabited the world, from ferns to redwood trees to the Venus flytrap.
Proterocladus is 200 million years older than the earliest known green kelp. One of its modern relatives is a type of edible seaweed called sea lettuce.
Proterocladus is the oldest unique green plant fossil. Fossils of possible older unicellular green plants are still controversial.
Plants were not the first to practice photosynthesis. They had an ancestor who apparently acquired the photosynthetic cell apparatus from a type of bacteria called cyanobacteria.
This ancestor of all green plants produced two main branches, one of which includes some aquatic plants and all land plants, while the other – the group to which Proterocladus belongs – consists entirely of aquatic plants.
"Proterocladus antiquus," said Virginia Tech's paleobiologist and co-author Shuhai Xiao, "is the sister of the evolutionary great-grandmother of all green plants living today."
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