The Cunoniaceae are a family of woody plants. They’re generally located in the southern hemisphere, with the centre of diversity around Australia, New Guinea and New Calendonia. However, they’re found around in Africa and South America. Their distribution suggests species formed by vicariance. Vicariance is when physical barriers separate populations. For the Cunoniaceae, the break-up of Gondwana caused the plants to diverge. There are only four members of the family in South America today but, in a study in Annals of Botany, Nathan Jud and Maria Gandolfo examine fossils that help explain how these distant species developed.
They describe the flowers of Cunoniantha bicarpellata gen. et sp. nov. identified in fossils from the Salamanca formation in Chubut, Argentina. The discovery is the second member of the Cunoniaceae to be found in the Salamance formation, joining Lacinipetalum spectabilum.
“The discovery of Cunoniantha and Lacinipetalum from the early Palaeocene of Argentine Patagonia provides strong evidence that the diversification of crown-group Cunoniaceae was under way by 64 Mya.” write the authors. “…these fossils also indicate that the family was widespread across Gondwana by the Palaeocene, when warm climates permitted floristic exchange between South America and Australia via Antarctica.”
For a while, A land bridge still connected South America to the Antarctic peninsula. As this land bridge fell, the climate cooled, meaning that the Antarctic was no longer a suitable habitat. Jud and Gandolfo also believed the same problem came to Chubut. “During the late Palaeogene and Neogene, much of Patagonia also became increasingly moisture-limited… Suitable habitat for Cunoniaceae in South America retreated northward with the montane forests of the rising Andes. This dramatic reduction in available habitat area could explain the loss of some Cunoniaceae from South America, whereas Lamanonia, Weinmannia, Eucryphia and Caldcluvia survive.”