Eocene Stromatolites from Green River Formation

This unique stromatolite comes from a famous fossil Laggerstat, the Green River Formation in Colorado. While Phanerzoic stromatolites such as this are far less common than in the Proterozoic, they are nontheless distributed worldwide; recently a 12 foot tall, living stromatolite dome was discovered in a freshwater, hypersaline lake in Africa. However, as we move forward in time through the Paleozoic, Mesozoic into the Cenozoic, stromatolitic reefs decrease in prevalence.

Interestingly, this Cryptozoon type stromatolite was very likely to have been built by plant-like green or red, algae (Chlorophycophyta), as opposed to cyanobacteria (that are Eubacteria). It is hypothesized that red and green algae appeared some 800 million years ago having acquired chloroplasts from eukaryotes through endosymbiosis to carry out photosynthetic metabolism using sunlight for their energy needs.

This specimen has been cut along one vertical plane and highly polished on one side to show the intricate detail of colonial growth that that appears more tube-like than laminar laminar layers and domes often seen in Pre-Cambrian stromatolites.

Of interest from a scientific perspective is the very young age. This Eocene stromatolite was formed long, long after Eubacterial-based stromatolite-building organisms like cyanobacteria had to begin to compete with other life forms, and hence had become very uncommon on earth, similar to modern times. The plant-like algae would have been a primary competitor with the Eubacteria during the Eocene.