Sandwiched between thick slabs of basalt in India, created by one of the largest volcanic eruptions in Earth’s history, palaeontologists found fossilized plants which they were unable to identify. That was in the 1970s and now researchers have been able to identify what they are. The fossils belonged to an extinct species in the Frankincense family of plants.

At the time, India was an island off the southeast coast of Africa. India’s continental plate was slowly inching toward Europe and Asia, and as it rafted past Madagascar, it broke the seal on a thin layer of Earth’s crust. Rivers of liquid rock poured onto a large area of the landscape. The eruptions occurred intermittently for nearly a million years, and they repeatedly killed any vegetation that grew during the interludes.

Using CT scanning technology, Steven Manchester, curator of paleobotany at the Florida Museum of Natural History, created 3D reconstructions of the original fossil specimens and others collected since. He showed these to a colleague, curator of botany at the Florida Museum, Walter Judd, who noticed something odd about the five triangular seeds inside.

They were identified as pyrenes, woody dispersal pods that give seeds an extra layer of protection. Examples include the hard stones at the cores of cherries, peaches, dates and pistachios, which prevent the seeds from being digested along with the rest of the fruit.

There are only a few plant groups that produce pyrenes, fewer still with fruits that contain five seeds arranged in a pentagram. Through a process of elimination, Manchester and Judd determined the fossils belonged to an extinct species in Burseraceae, the Frankincense family.

The volcanic activity that repeatedly devastated the landscape was active just before and after the asteroid impact that brought about the end of the Cretaceous period, and both are thought to have contributed to the extinctions that followed.

Most fossils from the Frankincense family have, up until now, been recovered from rocks that postdate the asteroid impact. The original fruits discovered in the 1970s were fossilized before that event. This makes them the oldest Burseraceae fossils discovered to date, which has important implications for the family’s origin. Scientists have a good idea of when plants in the group initially evolved, but it’s still unclear where they came from.

Ancient species of Burseraceae are a common component of fossil beds in southern England, the Czech Republic and parts of North America. Beginning roughly 50 million years ago, however, Earth’s climate began a long cooling process that ultimately resulted in the most recent Ice Ages. As temperatures fell, species in the Frankincense family seemed to reverse their preference for hemispheres. Today, there are more than 700 Burseraceae species, and most of them grow south of the equator.

The ancestors of modern Burseraceae species are thought to have first appeared somewhere in the north. Alternatively, a few early species may have had a global distribution but became isolated as continents drifted apart.

The fossils from India suggest the southern hemisphere may have been the real birthplace of the family.

Steven Manchester explained:

“It could be that we just don’t have rocks of the right age in Europe to indicate that they were there, but this shows that we can’t dismiss the southern hemisphere as a point of origin.”

BURSERACEAE IN THE LATEST CRETACEOUS OF INDIA: SAHNIOCARPON CHITALEY & PATIL is published in the International Journal of Plant Sciences