A mysterious fossil discovered in India in the 1970s has been identified as part of the Boswellia family, hinting at a southern hemisphere origin and reshaping our understanding of plant evolution. A paleontologist working on the outskirts of a village in India discovered small bead-like fossils embedded in the gray limestone that dotted the surrounding fields.

Paleontologists have determined that the mystery fruit, first discovered in the 1970s, is the oldest known fossil of the frankincense family. Source: Steven Manchester

The site became famous in archaeological circles for the discovery of unidentifiable plant fossils, including the fruit of an extinct species, which was named "Enigmocarpon". The new fossils proved equally frustratingly difficult to identify; over the next few decades, more such fossils were discovered in India, but scientists were almost never sure which plant they belonged to.

Breakthrough in fossil identification

Now, researchers say they have solved the mystery. Steven Manchester, curator of paleobotany at the Florida Museum of Natural History, used CT scanning technology to create a three-dimensional reconstruction of the original fossil specimen and other fossil specimens collected since then. He showed these specimens to his colleagues, who noticed something strange about the five triangular seeds inside.

Before CT scanning technology was widely used in paleontology, small fossils like these, less than 10 millimeters in diameter, were particularly difficult to study and identify. Photo credit: Steven Manchester

When shown the 3D images, "These are not seeds," Manchester recalled of his conversation with Walter Judd, curator of botany at the Florida Museum.

Pyrene is the woody spreading pod that gives the seeds an extra layer of protection. For example, hard rocks on the pits of cherries, peaches, dates, and pistachios can prevent the seeds from being digested along with the rest of the fruit.

Distinguishing seeds from pits, especially when they are the size of snowflakes, requires careful observation. The traditional paleobotanical method of gradually dissolving fossils in acid and then observing each new layer under a microscope has proven insufficient.

"If our specimens broke at just the right plane, I would be able to identify them, but with the material we have, I can't," Manchester said.

Although they look like seeds, these woody structures are actually pyrene, similar to the parts found in peaches and dates. Source: Steven Manchester

Frankincense Family Connection

Only a few plant groups produce pyrene, and even fewer have fruits that contain five seeds arranged in a five-pointed star. Through a process of elimination, Manchester and Judd determined that the fossils belonged to an extinct species of the genus Burseraceae.

Fossils of wood, leaves, fruits and flowers from this family are found elsewhere in India, often sandwiched between thick slabs of basalt formed by one of the largest volcanic eruptions in Earth's history.

CT scans allow paleontologists to quickly screen fossils without removing them from the rock matrix in which they are embedded. Source: Steven Manchester

Geological background and significance

At that time, India was an island off the southeast coast of Africa. India's continental plate is slowly moving toward Europe and Asia, breaking through the thin layer of Earth's crust as it drifts past Madagascar. Rivers of liquid rock cascaded down, creating a terrain the size of California and Texas combined. The eruptions continued on and off for nearly a million years, and they continued to kill any vegetation that grew during the intermittent periods.

"The fossils are preserved during lulls between eruptions," Manchester said. "Ponds and lakes formed on relatively fresh lava flows, and vegetation, including wood and seeds, was washed into them and covered with sediment."

The shield volcanoes that wreaked havoc were active both before and after the asteroid impact that kicked off the Cretaceous Period, and both impacts are thought to have contributed to subsequent extinctions.

So far, most fossils of the genus Boswellia have been found in rocks following asteroid impacts. The original fruit fossil discovered in the 1970s preceded that event. This makes them the oldest Boswellia fossils ever discovered, with important implications for the origins of the family. Scientists have a good idea of ​​when plants in this family first evolved, but they still don't know where they came from.

The fossils used in this study were collected over decades and will continue to be housed in natural history museums, allowing future researchers to learn more about their past. Image source: Florida Museum photo by Gerald Penson

Climate change and distribution shifts

Ancient Boswellia is a common component of fossil beds in southern England, the Czech Republic and parts of North America. However, starting about 50 million years ago, Earth's climate began a lengthy cooling process that ultimately led to the most recent ice age. As temperatures drop, species in the frankincense family appear to reverse their hemispheric preferences. Today, there are more than 700 species of Boswellia, most of which grow south of the equator.

The ancestors of modern frankincense are thought to have first appeared somewhere in the north. Alternatively, some early species may have been distributed across the globe but became isolated as continents drifted.

The fossils analyzed in this study are thought to be closely related to the species from which the frankincense resin comes. Image source: Illustration from Köhler's "Medizinal-Pflanzen" Volume 2

Influence on the origin of the frankincense family

Fossils from India suggest that the southern hemisphere may be the true birthplace of the frankincense family.

"It could be that we don't have rocks of the right age in Europe to show that they were there, but it shows that we can't deny the southern hemisphere as the origin," Manchester said.

The authors published their research report in the International Journal of Plant Sciences.

Compiled source: ScitechDaily