The earliest known eukaryotic fossils date back to around 2.1 billion years ago and provide evidence of a remarkable level of diversity and complexity, challenging previous assumptions about the simplicity of early eukaryotic life. Here are some examples:

Grypania spiralis:

Discovered in 1990, Grypania spiralis is a 1.9-billion-year-old microfossil that exhibits the hallmarks of eukaryotic complexity. It has a spiral structure, intricate cellular compartments, a possible nucleus, and the potential for locomotion using flagella.

Bangiomorpha pubescens:

Found in rocks approximately 1.2 billion years old, Bangiomorpha pubescens showcases the traits of multicellularity. It consists of branched filaments made up of individual cells, with specialized reproductive structures indicating a capacity for sexual reproduction.

Horodyskia moniliformis:

Dating back to around 1.6 billion years ago, Horodyskia moniliformis reveals a highly organized and complex anatomy. This unicellular organism exhibits distinct internal structures within its cells, including compartmentalized compartments containing photosynthetic pigments.

Ediacaran Fossils:

The Ediacaran Period (635 million to 541 million years ago) marks a remarkable diversification of complex multicellular organisms. Although lacking direct evidence of eukaryotic affinities, the intricate forms and large size of Ediacaran biota, such as Dickinsonia and Spriggina, are suggestive of advanced organizational complexity and specialization.

The presence of such diverse and complex eukaryotes in the early fossil record highlights the underestimated richness of life that existed long before the advent of advanced animals and plants. It underscores the notion that eukaryotic life underwent significant evolutionary innovation and diversification very early in Earth's history.