Rangeomorphs, the earliest animals on Earth, may have been shape-shifters

They lived in the ocean more than half a billion years ago and looked a lot like plants, but rangeomorphs are believed to be one of the earliest large animals on Earth.

Scientists from the University of Cambridge now believe these organisms may have been shape-shifters, with some growing up to two metres and changing their form (phenotype) to extract nutrients from their surrounding environment – a phenomenon described as ecophenotypic plasticity.

This ability allowed the rangeomorphs to dominate their environment for 30 million years, at a time when most other forms of life were microscopic in size, until the Cambrian Explosion 541 million years ago – a relatively brief period during which most of the major forms of life on Earth appeared.

“It’s probably too early to conclude exactly which geochemical changes in the Ediacaran oceans were responsible for the shift to large body sizes,” said Dr Jennifer Hoyal Cuthill of Cambridge University. “But there are strong contenders, especially increased oxygen, which animals need for respiration.”

Rangeomorphs looked a lot like modern ferns, with branching “fronds” forming geometric shapes known as fractals. These shapes are seen today in living tissue such as lungs and ferns and inanimate objects like snowflakes.

“What we wanted to know is why these large organisms appeared at this particular point in Earth’s history,” said Dr Hoyal Cuthill.

“They show up in the fossil record with a bang, at very large size. We wondered, was this simply a coincidence or a direct result of changes in ocean chemistry?”

The researchers say that while rangeomorphs were suited to their Ediacaran environment, when the conditions changed, they were doomed – and nothing quite like them exists today.

The results are reported in the journal Nature Ecology and Evolution.