The earth is warmer 34 million years ago-and even stranger. The Pangu supercontinent split. Dinosaurs no longer exist. But Antarctica contains non-glacial forests. Other continents look like squashed and smeared versions of their current selves. Mammals are everywhere-especially primates and rodents. “From New York to Los Angeles, to Canada, there are trees bouncing around,” said Seifert of North American primates. “But when this climate event happened 34 million years ago, they all disappeared.”
Some scientists believe that the level of carbon dioxide in the atmosphere drops below a critical threshold, causing the average temperature to drop and Antarctica to freeze. More sunlight is reflected by more ice, causing the temperature to drop further. The transition from the Eocene to the Oligocene is described as the transition from “greenhouse” to “igloo”.
Then, in Africa, the situation got worse. About 31 million years ago, a volcano near the equator, in today’s Ethiopia, erupted with devastating toxic smoke and relentless floods of molten basalt.
In the 11 million years before and after these events, the fossil record of North America, Europe, and Asia has been quite perfect. Scientists can calculate the fossils of which animals existed before the climate became cold, and which animals existed afterwards, and find out what was missing. However, Seifert said, “In this period, the fossil record in Africa is actually very incomplete.” This discrepancy bothers him, so his team tries to resolve the relationship between any fossil records they have.
In their research, Seiffert and de Vries focused on genealogy dating back 76 million years, when primates and rodents diverged. Specifically, they studied the teeth of two suborders of rodents (hystricognath and anomaluroid) and two suborders of primates (streptococcus and apes). These clades gave birth to existing species such as capybara, scaly flying squirrels, lemurs and us.
The researchers decided to reconstruct the family tree of the phylogenetic or evolutionary relationships of these groups from 56 million to 15 million years ago. Using teeth as a guide for “who is who”, they mapped the branches of lineages from fossils discovered in the late Eocene to descendants that survived to the Miocene about 20 million years ago. When they were finished, a clear gap appeared: the Miocene lineage came from a small part of early mammals. Researchers found that 63% of the lineages that existed in the late Eocene never passed the next epoch. They concluded that about 30 million years ago, due to environmental changes, these species must have disappeared. “There really is no other explanation,” Seifert said. “They must be extinct.”
The pedigree diversity allows the team to be aware of how many species have disappeared due to climate change, rather than how much these species may be different from each other-in other words, how many are different Anatomical Diversity is also extinct. For example, De Vries said, imagine a scenario where two species of birds become extinct. The two species may be very similar, or they may be completely different in size, genetics, or niche. “If you have a hummingbird and a flamingo, it is very different from if you have a dove and a dove,” she said.