How Lichen Thrived After an Asteroid Killed the Dinosaurs
“…The earth, that is sufficient, I do not want the constellations any nearer, I know they are very well where they are, I know they suffice for those who belong to them…” — Walt Whitman, Song of the Open Road
66 million years ago, the Earth was struck by great tragedy. An asteroid at least 6 miles long crashed into what is now the Yucatan peninsula causing waves of mass extinctions and leaving behind the Chicxulub crater.
The dinosaurs thought to have been brought down by the asteroid found themselves on the wrong planet at the wrong time in history. Even before the asteroid hit, ancient Earth’s environment was rebelling. Temperatures on the surface varied widely, volcanos erupted regularly, sea levels were changing, and the backbone of meat-eating dinosaurs’ food chain — the herbivorous dinosaurs, was not diverse enough to survive such a big hit.
Had non-avian dinosaurs reigned in a different time period, with different climatic considerations and greater prey diversity, some studies suggest they may have made it. In a press release, Dr. Steve Brusatte, who studies the details of the dinosaurs' demise said, “The dinosaurs were victims of colossal bad luck. Not only did a giant asteroid strike, but it happened at the worst possible time, when their ecosystems were vulnerable.”
This bad luck extended to some mammals, too. Ancient metatherian mammals, the ancestors of marsupial creatures like kangaroos and opossums, almost died out as well (which, humans rejoice, allowed “luckier” mammals to live and multiply).
One of the most devastating effects of the asteroid strike, was the destruction and extinction of many plant species. Some plants were destroyed in the initial strike and others were starved off by ash and smog that prevented the suns rays from reaching their famished leaves. Forests, and the birds that lived in them, were both decimated.
The way plants reacted to the asteroid made scientists at Chicago’s Field Museum wonder about lichen — an incredibly common organism that is composed of both a photosynthesizer and a fungus. While fungus would surely feast on the decay that surrounded them, plant-like photosynthesizers would die and with no sunlight to trigger their carbohydrate forming reactions. So, which side wins?
The answer was found when the Field Museum collaborated with scientists at Academia Sinica, Brigham Young University, and Kasetsart University. In a press release, the published report’s first author, Jen-Pang Huang said that the team initially thought lichens would have had the same fate as plants, but they instead found that lichen, “…seized the chance and diversified rapidly.” Because some lichen can grow structures that resembled plants, they were able to take over their ecological niche.
Fungi are avid decomposers that thrive on dead organic matter, and because they’ve been around for so long, biologists know how often they mutate — which can then be used to determine the common ancestor of two fungal species.
With this knowledge at hand, the researchers took DNA from lichen fossils up to 400 million years old and fed these sequences to an algorithm that creates a phylogenetic tree — a small portion of the tree of life that visualizes when certain species first emerged or how two or more species are related.
They found that 66 million years ago, just after the great dinosaur catastrophe, there was a huge bloom in lichen species, particularly those that formed larger, leafier structures.
Other groups of lichen were completely unphased by the firey chaos surrounding them — they didn’t seem to gain or lose anything. Still, other groups went extinct completely, allowing leafy lichen to take over. According to a press release, scientist and author H. Thorsten Lumbsch was “really happy when I saw that not all the lichens suffered.”
Understanding how life goes on after a catastrophe is as cool as it is predictive. Lumbsch explains that, “If you could go back 40 million years, the most prominent groups in vegetation, birds, fungi — they’d be more similar to what you see now than what you’d see 70 million years ago. Most of what we see around us nowadays in nature originated after the dinosaurs.”
The molecular data the team used to reconstruct lichen’s family tree gives some insight into how the Earth might change in the ongoing, Anthropocene mass extinction. And the lichens living today can be used to measure how our ecosystems are holding up. As first author Jen-Pan Huang said, “Lichens are environmental indicators — by simply doing a biodiversity study, we can infer air quality and pollution levels. Before we lose the world’s biodiversity, we should document it, because we don’t know when we’ll need it.”
Click on the link below to learn how climate change affects the food chain — starting from the bottom up.
