December 3. Recovery from extinction

To begin today I want to mention a new podcast I’ve just found out about, called Evolution Talk. It just began in August 2014 and as the title suggests, it’s all about evolution, including Darwin and other scientists that formulated the theory. It’s produced by Rick Coste on a weekly schedule, and I recommend it to you. It’s on iTunes, and I have a link on my blog to it as well. You can find information at EvolutionTalk.

Today’s topic is the recovery from the extinction at the end of the Cretaceous. Some of the great extinctions in earth history clearly impacted the planet for a long time. The Permian extinction in particular, together with the single-continent nature of Pangaea, seems to have resulted in an early Triassic that was pretty antagonistic for life for a few million years, at least. 

Life seems to have recovered from the end-Cretaceous event relatively quickly, which intuitively could be seen to support the idea of a very specific event, the asteroid impact, as the primary cause. 

One study led by researchers at MIT even suggests that the recovery of oceanic algae and cyanobacteria was underway as soon as just 100 years after the impact. Since those microorganisms are the base of the food chain, their recovery would have paved the way for the expansion of other life as well, but if you look at the recovery in other ways, it may have taken more time, even much more, a typical million years or so. 

The argument has been made that survivors were animals that could forage on dead plant or animal matter – which was presumably in abundance – rather than those that fed on living plants. A study of the interlinked recovery of plants and insects, led by researchers at Penn State, found that plant diversity was very low for 800,000 years after the extinction event, and for 8 million years, generally, plants and insects remained relatively low in diversity. But there were some exceptions where plants and bugs thrived, quite early in the Paleocene, the epoch immediately after the extinction. That kind of makes sense to me, that there might have been refuges, or locations where the devastation was not so intense, that could maintain or re-develop their diversity relatively quickly.

However long the recovery took, it certainly did happen. As the phytoplankton in the oceans recovered, so did the surviving bony fishes. On land in the course of the 10 million years after the extinction, the Paleocene epoch, mammals and birds both diversified and became larger than their Cretaceous ancestors. It would appear that being small was no longer such an advantage, with the big predatory dinosaurs gone. By the end of the Paleocene, 56 million years ago, and into the following Eocene Epoch, some flightless birds were growing to six feet in height. Mammals mostly were still small compared to later in the Cenozoic, but there were several different mammals that reached a meter or more in length. I think it is clear that they were getting bigger, and we’ll talk about some of the mammals and birds of the Cenozoic later this month.

I have links below to reports on the nature of the recovery from the end-Cretaceous extinction.

—Richard I. Gibson

LINKS:
Chaotic recovery?

Fish diversify
Rapid recovery? 
Recovery intervals
Recovery dynamics 
Paleocene mammals