Was Europe covered with forests or savannahs eight million years ago?

An article authored by researchers of the University of Helsinki published in a scientific journal has given rise to criticism. According to palaeontologist Mikael Fortelius, the critics have misunderstood the article.

In March 2019, a minor storm brewed up within the sphere of palaeontology. The swell was raised by an article entitled The rise and fall of the Old World savannah fauna and the origins of the African savannah biome  published in the Nature Ecology & Evolution series and the subsequent debate.

“We’ve received a lot of confused queries from our international colleagues, many of them wanting to know what the controversy is about,” explains Mikael Fortelius, professor of evolutionary palaeontology at the Department of Geosciences and Geography.

The article, an international collaboration led by the Helsinki team, dealt with the origins of the African savannah. According to the researchers, the savannah fauna is a remnant of a savannah-like environment dating back 5–13 million years, also known as a palaeobiome, extending from southern Africa through Europe all the way to China.

“The environment was grasslands speckled with trees here and there. In an area as extensive as this, the fauna and flora of course varied.  However, animals and plants from the same groups of species were found all over,” Fortelius says.

Some 15 million years ago, similarities between the fauna and flora of Africa and Eurasia began to increase, as the African continent collided with Europe, forming a landbridge. Animals in particular started migrating between the continents. From Africa, Europe gained primates and the Proboscidea, while Eurasia gave Africa relatives of the pig and the rhinoceros.

“This was our main message, which has not yet been questioned. The controversy started over a side issue,” Fortelius says.

Pollen versus teeth

Susanne Renner, a German botanist, seized on the savannah-like environment described by the researchers that extended from Africa to China, claiming in a blog entry entitled When mammalian tooth heights predict a savanna, but plant fossils don’t published on the Nature website that they were mistaken. The blog refers to an article entitled Plant fossils reveal major biomes occupied by the late Miocene Old-World Pikermian fauna  published in the Nature Ecology & Evolution series. According to Renner and the other authors of the article, there was no uniform environment in the area.

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As grounds for their argument, the authors stated that conifer pollen has been discovered around the region described by the University of Helsinki scholars as a savannah in the broad sense. According to Renner, this finding indicates that the location was covered by forests.

“They have misread our article. We don’t posit that the region’s fauna and flora were entirely uniform. Of course there was regional variance, which also comes out in the illustrations of our original article. Nor do we claim that the region was treeless. However, the idea of a forest environment is erroneous, as large mammals would not have survived in forests. And yet, their remnants have been found in the region,” Fortelius states.

Renner also criticised the dataset and methodology used by the University of Helsinki researchers as too inaccurate. As a source, the authors of the original article used teeth of large mammals. Renner believes their dental analysis conflicts with the pollen findings.

“By examining the teeth of large herbivorous mammals, it’s entirely possible to determine the environment they inhabited, since the teeth of the species that populate a given region mirror the nature of nutrition available there. Herbivores that graze on grassland or shrubland and trees have different teeth. We calculated the average features of teeth in mammalian communities and related them to environment and climate,” says Assistant Professor Indrė Žliobaitė from the Department of Computer Science.

“Furthermore, we don’t claim that coniferous trees didn’t grow in the region. It’s just that their effect is not seen in teeth, as it's a rare species that uses them as food,” Fortelius points out.

Debate is good

Fortelius and Žliobaitė emphasise that they are not annoyed by the debate.

“It’s good that people are talking about it. That’s how things get attention,” Žliobaitė says.

“This is what science is: arguments and counter-arguments. We of course have to defend our findings and methods,” Fortelius chuckles.

What about the African savannah?

Gradually, the climate became increasingly arid. Already roughly six million years ago there were deserts in northern Africa and the Middle East, preventing animals and plants from dispersing between Africa and Eurasia.

In Europe, forests started covering increasingly large swathes of the region, with forest fauna becoming more prevalent. Then again, environmental changes in sub-Saharan Africa were less pronounced. The region remained a sparsely wooded savannah, also retaining a savannah-like fauna.

Mikael Fortelius: Behind the paper: The painting on the wall: what’s the matter with dental ecometrics? Mar 18, 2019, Ecology and Evolution.