Billion-year-old fossil, a missing link in the evolution of animals?

[Astronuc]

https://phys.org/news/2021-04-billion-year-old-fossil-reveals-link-evolution.html

A billion year old fossil, which provides a new link in the evolution of animals, has been discovered in the Scottish Highlands.

A team of scientists, led by the University of Sheffield in the UK and Boston College in the U.S., has found a microfossil which contains two distinct cell types and could be the earliest multicellular animal ever recorded.

The fossil reveals new insight into the transition of single celled organisms to complex multicellular animals.
. . .
The fossil has been described and formally named Bicellum Brasieri in a new research paper published in Current Biology.

I used to have some literature on ancient single cell organisms, but I haven't seen it in decades.

https://www.cell.com/current-biology/fulltext/S0960-9822(21)00424-3
Sediments of the Torridonian sequence of the Northwest Scottish Highlands contain a wide array of microfossils, documenting life in a non-marine setting a billion years ago (1 Ga). Phosphate nodules from the Diabaig Formation at Loch Torridon preserve microorganisms with cellular-level fidelity, allowing for partial reconstruction of the developmental stages of a new organism, Bicellum brasieri gen. et sp. nov.

 

[BillTre]

These fossils are really well preserved, and very early!
More sophisticated embryos from something like 5-600 million years ago have also been found as Phosphatic fossils. Some look quite like embryos of invertebrate lineages that are still around today.

Evolutionary relations of the earliest metazoans are not all that clear.
There are some obscure groups (like Placozoa) that are not that advanced over a flattened bag of cells (with a outer layer of a different kind of cells), and could be hypothesised to be related in some way to these guys, making any connects between living animals and fossils can be difficult.