Earth has seen great changes since the close of Eocene 33 million years ago. Temperatures dropped slowly and glaciers moved towards the equator in a slow reverse of what we see today.
It was a devastating loss of life on the Asian continent. The colossal changes to Asia were devastating for Africa's biodiversity. However, Africa was protected by the warmth of its tropics and seemed to be unaffected. Or so we thought.
A team of US researchers published a study that found we were not looking at the fossil record in the right way.
Research suggests that mammals across Africa and the Arabian Peninsula suffered significant declines due to the cold climate. Nearly two-thirds of their peak diversity disappeared 30 million years ago.
It's not clear what caused each loss, but there are plenty of possibilities due to the high temperature fluctuations and intense volcanic activity in the area.
The ecological niches that were left by the extinction event didn't disappear for very long, regardless of what caused it.
Steven Heritage, a Duke University biologist, says that it is clear that there was an extinction event and then a recovery period.
Many of the information we have about the changing climate during the transition from Eocene into the Oligocene comes from studies of oxygen isotope changes in sediment cores taken from the ocean floor.
These clues, along with evidence of glacier growth and fluctuating sea levels, give us a broad picture of how the planet was changing.
However, signs at more local levels can look a bit patchy. This is because they rely more on modeling and close inspection of fossils that appear sporadically.
Recordings taken on dry ground can give mixed results, so it's not surprising that there has been much debate about the effects of global cooling on the masses around the Equator.
One hand, evidence suggests that animals like the ancestral relatives of modern Lemurs have disappeared from Africa's north east. Other studies show that Africa has experienced very few environmental changes or none at all.
Because fossil records are often patchworked, they can be difficult to interpret. Researchers can still extract a wealth of information from a few bones, even though not all species have their remains preserved in a neat and tidy location.
The fossils of five mammal groups were collected by the team, which included rodent and squirrel-like anomalures as well as two primate groups. One was occupied by our ancestors.
The researchers created a family tree from these samples that represented the dates of losses and appearances for each. The scientists could use statistical tools to determine when losses occurred in certain areas and link them with global events.
Researchers could examine the similarities within similar groups to see how species have diversified to fill the gaps left by the animals that died.
Consider the teeth of an animal. It is possible to see how species quickly adapted to new food sources by the subtle differences in the shapes of their teeth over time.
Dorien de Vries from the University of Salford, leads author, "We see a large loss in tooth variety, and then there is a recovery period with dental shapes and adaptations."
Our primate ancestors are among the most affected. The diversity of anthropoid teeth dropped to almost nothing 30 million years ago. This was so severe that only one type of dental morphology survived, restricting the foods that their descendants could consume.
These bottlenecks are common in the evolutionary record. Given the pressure we are putting on so many ecosystems all over the world today, it could be crucial to understand how these bottlenecks affect species.
We survived because of that tooth design. Our species may never have seen the light if it wasn't for that tooth design.
De Vries says, "It was really a reset button."
This research was published by Communications Biology.
