Fossils are integral tools used to describe not only extinct species, but the evolutionary history of the species that live today. Already, we have learned so much about Earth’s biology from the fossil record. A few examples include the evolution of modern birds from small, feathered dinosaurs that scurried along the forest floor nearly 65 million years ago, and the development of vascular plant tissues during the Devonian, which vastly altered the climate of this planet. The ability to date the origin of rock formations is one of the best qualities fossil evidence has to offer, because not only can we study the fine morphological details of past organisms, but we can understand when they showed up along Earth’s ancient history.
Unfortunately for us, there are biases in the fossil record. So, not all of Earth’s past species are represented equally. In a perfect world, the 99% of species that have gone extinct before us would show up in pristine condition throughout the fossil record. We would be able to build extensive phylogenetic relationships by simply looking at rocks. It would be incredible, but you and I both know, we don’t live in a perfect world. We live in a world in which some organic structures are more easily fossilized while some rapidly deteriorate before sediments can settle and encase the deceased organism.
Here are some of the main biases:
- Size-Larger biological structures are more easily found than smaller ones. Also, humans are generally more interested in the organisms that can fill up a large space within a museum, than a tiny fossil that needs to be appreciated with a microscope.
- Time-Older structures are rarer than more recent ones. The older a fossil is, the more likely it is to be destroyed through large scale geological processes.
- Organismal structure-It’s hard to imagine a time before calcium carbonite skeletons and shells, but these organisms are pretty new to Earth’s scene, with the first large shell forming animals, the trilobites, initially appearing around 520 million years ago. These shell and later bone forming organisms are widely represented throughout the fossil record while soft bodied organisms are nearly absent.
- Habitat-Some areas have better conditions for possible fossilization. This is why bottom dwelling marine species, fresh water stream organisms, and plants living on the banks of such streams have a more pronounced occurrence in the fossil record.
There is more bias within the fossil record, but I would say these factors are the main players. With this, you can understand why so few fungi are represented within the fossil record. Mushrooms are small, soft, and they rapidly decompose. When we do find a fungal fossil, the mycological world electrifies, hoping to learn more about our ancestral forest floor. A little more than a year ago, this is exactly what happened when Sam Heads and his team uncovered and described a fungal fossil from Northeast Brazil. Before this, the only ancient fungi we’ve come across were preserved in amber. We have known that fungi have been interacting with Earth’s first terrestrial ecosystems, but the fossil found here, named Gondwanagaricites magnificus is an exciting find to say the least.
Its genus name, Gondwanagaricites combines the place where the fossil was found-the ancient supercontinent called Gondwana, and the Greek word for mushroom, agarikon. The species name, magnificus is the Latin adjective for magnificent, referring to its immaculate fine details preserved over 113–120 million years. Normally, you just don’t find this type of detail in most soft bodied organisms, so yeah, it is magnificent. Just how did an organism like this, that breaks down so rapidly become preserved so pristinely?
You can thank the type of mineral deposition called Lagerstätten for the preservation of this soft bodied beauty. In some rare cases, like when this fungus first fell into the shallow, inland sea, present in Northeast Brazil at the time, many conditions were just right. The Crato Formation where this mushroom was found represents the Goldilocks principle in the fossil realm. When this mushroom found its final resting place, it was buried rapidly. This along with the present water conditions reduced decomposition with low levels of oxygen, nearing anoxia. Without oxygen, most bacteria can’t carry out their metabolic processes, so this mushroom remained in an unperturbed state, allowing fossilization to occur.
This fungus was then encased in layers of limestone. Overtime, the limestone exchanged minerals with the fungus, essentially turning the fruiting body into rock. By looking at its morphology, Gondwanagaricites magnificus looks like a fungus within the family Strophariaceae. Other taxonomic candidates include the Agaricaceae, Tricholomataceae, and Bolbitiaceae. We can’t confirm this claim with DNA evidence, because its genetic makeup is long gone, but we can still take comfort knowing for a fact, that gilled mushrooms played multiple roles 113–120 million years ago. Gondwanagaricites magnificus could be an extinct lineage of fungi, but its appearance intrigues the mycological community, resembling extant species we see today. Could this fossil be the ancestor of such living families? I sure think so.