If you had looked up 66 million years ago, you might have seen a bright light for a split second as a mountain-sized asteroid burned through the atmosphere and slammed into Earth. It was spring and the literal end of an era, the Mesozoic.
If you had somehow survived the initial impact, you would have witnessed the devastation that followed. Raging firestorms, megatsunamis and a nuclear winter that lasts months to years. The 180 million year reign of non-avian dinosaurs was over in an instant, as was that of at least 75% of the species that shared the planet with them.
After this event, known as the Cretaceous-Paleogene mass extinction (K-Pg), a new dawn dawned for Earth. Ecosystems recovered, but life within them was different.
Many iconic pre-K-Pg species can only be seen in a museum. The terrible Tyrannosaurus rexThe Velociraptorand the winged dragons Quetzalcoatlus The genus was unable to survive the asteroid and is limited to a long history. But when you walk outside and smell the roses, you will find yourself in the presence of ancient lineages that bloomed in the ashes of K-Pg.
Although the living species of roses are not the same ones with which the earth was shared Tyrannosaurus rexTheir lineage (family Rosaceae) originated tens of millions of years before the asteroid impact.
And in this respect roses are a not unusual lineage of angiosperms (flowering plants). Fossils and genetic analyzes suggest that the vast majority of angiosperm families arose before the asteroid.
The ancestors of the ornamental orchid, magnolia and passionflower plants, the grass and potato plants, the medicinal daisy plants and the herbaceous mint plants all shared the earth with the dinosaurs. In fact, the explosive evolution of angiosperms into today’s approximately 290,000 species may have been facilitated by K-Pg.
Angiosperms appeared to have taken advantage of the new beginning, much like the early members of our own lineage, the mammals.
However, it is not clear how they did this. Angiosperms, so fragile compared to dinosaurs, cannot fly or run to escape harsh conditions. They rely on sunlight for their existence, but that has been extinguished.
What do we know?
Fossils in different regions tell different versions of events. It is clear that there was high angiosperm turnover (loss and resurgence of species) in the Amazon at the time of the asteroid impact, and there was a decline in herbivorous insects in North America, suggesting a loss of food plants. But other regions, such as Patagonia, show no pattern.
A 2015 study that analyzed angiosperm fossils from 257 genera (families typically contain multiple genera) found that K-Pg had little effect on extinction rates. However, this result is difficult to generalize to the 13,000 angiosperm genera.
My colleague Santiago Ramírez-Barahona from the Universidad Nacional Autónoma de México and I took a new approach to solving this confusion in a recently published study Biology letters. We analyzed large angiosperm family trees mapped in previous work based on mutations in DNA sequences from 33,000 to 73,000 species.
This type of tree thinking has laid the foundation for important insights into the evolution of life since the first family tree was drawn by Charles Darwin.
Although the family trees we analyzed did not contain extinct species, their shape contains clues about how extinction rates have changed over time, through the way branching rates ebb and flow.
The extinction rate of a lineage, in this case angiosperms, can be estimated using mathematical models. The method we used compared ancestral ages with estimates of how many species should appear in a family tree, based on what we know about the evolutionary process.
Additionally, the number of species in a family tree was compared with estimates of how long it takes for a new species to evolve. This gives us a net diversification rate – how quickly new species appear, adjusted for the number of species that have disappeared from the lineage.
The model generates time periods, such as a million years, to show how the extinction rate changes over time. And the model allows us to identify periods of high extinction rates. It may also indicate times when major changes in the emergence and diversification of species occurred, and when mass extinctions may have occurred. It shows how well the DNA evidence supports these findings too.
We found that extinction rates appear to have remained remarkably consistent over the past 140 to 240 million years. This finding highlights how resilient angiosperms have been over hundreds of millions of years.
We cannot ignore the fossil evidence showing that many angiosperm species have disappeared around K-Pg, with some locations more affected than others. However, our study appears to confirm that the lineages (families and orders) to which the species belonged continued undisturbed and created life on Earth as we know it.
This is different from non-avian dinosaurs, which disappeared in their entirety: their entire branch was pruned.
Scientists believe that the resistance of angiosperms to the K-Pg mass extinction (why only leaves and branches of the angiosperm tree were pruned) can be explained by their adaptability. For example, their development of new seed dispersal and pollination mechanisms.
They can also duplicate their entire genome (all the DNA instructions in an organism), creating a second copy of every single gene that selection can act on, potentially leading to new forms and greater diversity.
The sixth mass extinction we are currently facing could follow a similar path. A worrying number of angiosperm species are already at risk of extinction, and their demise will likely spell the end of life as we know it.
It’s true that angiosperms can thrive again from a diverse collection of survivors – and they could outlive us.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Image source: Avis Yang / Unsplash