Explosive fossil fruits discovered buried under ancient Indian lava flows

Just before the final scenes of the Cretaceous period, India was a rogue subcontinent on a collision course with Asia. Before the two landmasses merged, however, India hovered over a “hot spot” in Earth’s crust, triggering one of the largest volcanic eruptions in Earth’s history, which likely contributed to the extinction. dinosaurs.

In a recent study, scientists excavating fossilized remains of plant material stuck between layers of volcanic rock describe a new plant species based on the presence of distinctive fruit capsules that likely exploded to disperse their seeds. The fossils may be the oldest fruit discovered to date from the euphorbia family (Euphorbiaceae), a group of plants with more than 7,000 species, with well-known representatives that include poinsettia, castor bean, rubber trees and crotons.

The fossilized fruits were discovered near the village of Mohgaon Kalan in central India, where remnants of the once widespread volcanic rock lie just below the surface in an intricate mosaic.

“You can walk around these hills and find pieces of chert that have just weathered through the topsoil,” said lead author Steven Manchester, curator of paleobotany at the Florida Museum of Natural History. “Some of the best collections are when farmers have plowed the fields and moved the pieces aside. For a paleobotanist, it’s like finding little Christmas presents all along the fields.”

Although there is some uncertainty as to the timing, the volcanic eruptions are thought to have lasted for up to 1 million years, occurring in prolonged pulses that covered the surrounding landscape with thick layers of lava up to 1 mile deep. Today, the basalt rocks left behind by eruptions, known as the Deccan Traps, cover an area larger than the state of California.

The most violent of volcanic events, which occurred at the end of the Cretaceous, may have been triggered by the impact of an asteroid on the other side of the world.

“The impact in the Yucatan may have caused seismic disturbances that actually disrupted the regime on the other side of the planet, causing lava to erupt,” Manchester said.

New species have grown in stunted forests

Sandwiched between basalt, paleontologists found shales, chert, limestone and clays piled up in a giant layer cake of alternating bands, most of which are rich in fossilized remains of plants and animals. These fossils provide insight into what appear to have been relatively quiet periods of stability between massive lava flows.

The newly described species were likely shrubs or small trees that grew near hot springs created by the interaction of groundwater with naturally heated rock below the surface, similar to present-day environments in Yellowstone National Park. At the time of their preservation, India was making its way through the equatorial zone of the Earth, creating warm and humid conditions that supported a number of tropical species, including bananas, water ferns, mallows and relatives of modern crape myrtles.

Petrified wood is a common find in Deccan traps, but most of them have small diameters, suggesting a lack of large trees whose conspicuous absence has prevented scientists from trying to piece together history. environment of the region.

“India was positioned at a low latitude, so we were expecting to find big forest giants. But that’s not what we’re seeing,” Manchester said.

It is unclear why the trees could not achieve greater stature, but Manchester suspects that the underlying basalt may have limited root growth. Alternatively, he said, the plants could have been part of young forests growing in volcanically active regions, which would have wiped out the surrounding vegetation before it had a chance to mature. “You’re more likely to get preserved fossils from recent eruptions, which create lots of volcanic ash that can bury and preserve plants,” he said.

Scientists peel off layers of mysterious fruit

The fruits of the new species were found perfectly preserved in a chert matrix by co-author Dashrath Kapgate. But with only the fruits to go on, figuring out which plants they belonged to required a significant amount of extensive research.

“It didn’t really match any known plant group,” said lead author Rachel Reback, who studied the fossils while working as an undergraduate researcher at the Florida Museum. “We ended up having to take a lot of CT scans of not only the fossils we had, but also the fruits of living species so we could compare them directly.”

The researchers ultimately determined that the fossils belonged to the euphorbia family by studying similar fruit specimens provided by the Smithsonian Institution. However, one of the fossils was so different from anything they had seen that they determined it represented an entirely new species within the fossil genus. Euphorbiotheque.

The orientation of the fibers inside the fruit indicated that they were probably explosive, a common means of seed dispersal in other spurges, including cassava, rubber trees, crown of thorns, and castor bean. Once the fruits of these species have ripened, they begin to dry out, losing up to 64% of their original weight, which creates tension in the stiff outer layers. Once enough water has evaporated, “you hear this loud pop, and seeds and pieces of fruit fly everywhere,” Manchester said, describing the process in rubber trees. “We think this is also the case for these two fossil species, because we see the same anatomy, where the fibers of the inner and outer layers of the fruit wall are oriented in opposite directions, which helps to create a couple .”

India an incubation chamber for new groups and species

Fossils like these offer tantalizing clues to paleontologists about the origin and movement of species. About 140 million years ago, conjoined India and Madagascar began to drift away from the supercontinent Gondwana in the southern hemisphere, taking with them plants and animals that evolved in isolation throughout the Cretaceous.

By the time India finally crashed into Eurasia, 10 million years after the extinction of the dinosaurs, it had given rise to an incredible diversity of life found nowhere else. They are probably the first grapes that evolved in India, just like the ancestors of whales. As the Himalayas took shape above the sutured landmasses, new groups of insect-eating pitcher plants, flightless birds, lizards, freshwater crabs, scorpions and praying mantises all took shape. left India to enter new environments in Europe and Asia.

Manchester hopes these fossils and others like them emerging from the traps of the Deccan will help shed light on the distribution of species at a critical time in Earth’s history. “What were the environments like in India at a time when it was not yet connected to Eurasia and how did they compare with other regions at that time? he said. “It’s like filling in the pieces of a puzzle.”

The team published their results in the International Journal of Plant Science.