An unsolved mystery puzzling the world of paleobotany since the 1970s has been solved.
Researchers determined that the fossilised fruits of an unknown extinct plant species come from the earliest known fossil of the family Burseraceae. It’s the plants in this family that produce Frankincense and Myrr.
First uncovered in India in the early 1970s, the small, bead-like fossils were embedded in a site notorious for turning up difficult-to-identify plant fossils.
Further fossils were discovered throughout India over the subsequent decades, with the extinct species fittingly given the name “Enigmocarpon”. Until now, scientists have had no success concluding what type of plant they belonged to.
More recently, Steven Manchester, curator of paleobotany at the Florida Museum of Natural History in the US, created 3D reconstructions of the fossil specimens using CT scans. But it wasn’t until he showed these to a colleague that the true breakthrough was made – his colleague noticed something odd about the 5 triangular seeds inside.
“When I showed him the 3D images, he said ‘those aren’t seeds, those are pyrenes,’” Manchester recalls of his colleague Walter Judd, courtesy curator of botany at the Florida Museum.
Pyrenes, commonly known as a pits or stones, are the woody dispersal pods found in fruits called drupes or drupelets. Their function is to protect the seeds by preventing them from being digested when eaten.
Well-known examples include the hard stones at the cores of cherries, peaches, dates, and raspberries. In this case, however, it had been extremely difficult to tell the difference between a seed and a pyrene due to their size: only about that of a snowflake.
“If we had specimens that fractured at just the right plane, I would have been able to recognise them, but with the material we had on hand, I couldn’t tell,” Manchester says.
Once it was determined that these fossils contained pyrenes, the rest was simply a process of elimination. There are only a few plant groups that produce pyrenes, and even fewer that produce fruits that contain five seeds arranged in a pentagram.
Therefore, the fossils must belong to an extinct species in the family Burseraceae.
This the family also contains trees from the genus Boswellia, which produce the aromatic resin known as Frankincense, and Commiphora, which produce the resin known as Myrr. Both are used in incense and perfumes.
They are also the oldest fossils of this family discovered to date. Most have been recovered from rocks that postdate the asteroid impact that wiped out the dinosaurs 66 million years ago, but these fruits were fossilised before that event.
The finding suggests that the ancestors of modern Burseraceae species may have first appeared in the southern hemisphere, which is where the Indian Plate was located at the time.
“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,” says Manchester.
The new study is published in the International Journal of Plant Sciences.
