Flowering plants survived the asteroid that killed the dinosaurs, and may outlive us

If you had looked up 66 million years ago, you might have seen, for a split second, a bright light like a mountain-sized asteroid burning through the atmosphere and crashing into Earth. It was springtime and the actual end of the Mesozoic Era.

If you somehow survived the initial impact, you would have witnessed the devastation that followed. Raging firestorms, massive tsunamis, and nuclear winters that last from months to years. The 180-million-year reign of the non-avian dinosaurs ended in the blink of an eye, as did at least 75% of the species that shared the planet with them.

In the wake of this event, known as the Cretaceous-Paleogene (K-Pg) mass extinction, a new dawn came for Earth. The ecosystems had revived again, but the life that inhabited them was different.

Many famous pre-K-Pg types can only be seen in the museum. The massive one Tyrannosaurus rexthe Velociraptorand winged dragons Quetzalcoatlus The race was unable to survive the asteroid and is confined to deep history. But if you take a walk outside and smell the roses, you will be in the presence of ancient lineages that flourished in the ashes of K-Pg.

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Although the living species of roses are not the same as the ones I shared the land with Tyrannosaurus rexTheir lineage (the Rosaceae family) arose tens of millions of years before the asteroid hit.

Roses are not an unusual breed of angiosperms (flowering plants) in this regard. Fossils and genetic analysis indicate that the vast majority of angiosperm families arose before the asteroid.

The ancestors of the ornamental orchid families, the magnolia and passionflower families, the grass and potato families, the medicinal daisy family, and the herbaceous mint family, all shared the land with dinosaurs. In fact, the massive evolution of angiosperms to approximately 290,000 species today may have been facilitated by K-Pg.

Angiosperms seem to have benefited from a fresh start, similar to the first members of our lineage, the mammals.

A purple flower growing from a crack in the sidewalk
The flowers are surprisingly flexible.

However, it is not clear how they did this. Angiosperms, which are extremely fragile compared to dinosaurs, cannot fly or run to escape harsh conditions. They depend on sunlight for their existence, which has been erased.

What do we know?

Fossils found in different areas tell different accounts of the events. There was clearly a rise in angiosperm turnover (loss and reemergence of species) in the Amazon when the asteroid hit, and a decline in plant-eating insects in North America, suggesting a loss of food plants. But other regions, such as Patagonia, show no pattern.

A 2015 study analyzing fossil angiosperms from 257 genera (families typically contain multiple genera) found that K-Pg had little effect on extinction rates. But it is difficult to generalize this result to 13,000 angiosperm genera.

My colleague Santiago Ramirez Barahona, from the National Autonomous University of Mexico, and I took a new approach to resolve this confusion in a study we recently published in the journal Biology Letters. We analyzed large angiosperm family trees, which previous work had drawn through mutations in the DNA sequences of 33,000 to 73,000 species.

This way of tree thinking has laid the foundation for major insights into the evolution of life since Charles Darwin wrote the first family tree.

A diagram with handwritten notes on the sides and bottom
Charles Darwin’s first diagram of an evolutionary tree from 1837.

Although the family trees we analyzed did not include extinct species, their shape contains clues about how extinction rates change over time, through the way the rate of branching ebbs and flows.

The rate of extinction of a lineage, in this case angiosperms, can be estimated using mathematical models. The method we used compared the age of the ancestor with estimates of how many species should appear in the family tree according to what we know about evolution.

It also compared the number of species in a family tree with estimates of how long it takes for a new species to evolve. This gives us the net diversification rate – how quickly new species appear, adjusted for the number of species that have disappeared from the lineage.

The model creates time scales, such as million years, to show how the extinction rate varies over time. The model allowed us to identify time periods that witnessed high extinction rates. It can also indicate times when major shifts in species creation and diversification occurred, as well as when there may have been a mass extinction event. It shows how much DNA evidence supports these findings as well.

We found that extinction rates appear to be remarkably constant over the past 140-240 million years. This discovery highlights how resilient angiosperms have been over hundreds of millions of years.

We cannot ignore fossil evidence showing that many angiosperm species have already disappeared around K-Pg, with some sites being more damaged than others. But as our study confirms, the lineages (families and orders) to which species belong persisted undisturbed, creating life on Earth as we know it.

This is different from the case of non-avian dinosaurs, which disappeared completely: their branch was completely pruned.

Scientists believe that the resilience of angiosperms in the face of the K-Pg mass extinction (why only the leaves and branches of the angiosperm tree were pruned) can be explained by their ability to adapt. For example, their development of new mechanisms for seed dispersal and pollination.

They can also replicate the entire genome (all the DNA instructions in an organism) providing a second copy of each gene on which selection can act, potentially leading to new forms and greater diversity.

The sixth mass extinction event we are currently facing may follow a similar path. An alarming number of angiosperm species are already threatened with extinction, and their demise will likely spell the end of life as we know it.

It is true that angiosperms may flourish again from a diverse group of survivors – and may outlive us.

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