Two Fruit Fossils, Millions Of Years Old, Discovered In Washington. Know Why It Is Surprising

Recently, a team of researchers analysed the fossil plant specimens. The research details two fossil winged fruits from the genus Ceratopetalum.

Exposed rock showing top-down view of fruit with an annular nectary, one entire wing, a partial wing, and three abraded wings (arrows). (Credit: Tang, et al./University of Kansas)

New Delhi: The discovery of two well-preserved ancient fossil plant specimens in Washington, United States of America, is prompting paleobotanists to rethink how plants might have been dispersed during the Late Cretaceous, between 66 million and 100 million years ago. 

Recently, a team of researchers analysed the fossil plant specimens. The study, conducted by researchers at the University of Kansas (KU), US, was published in the journal, New Phytologist.

The research details two fossil winged fruits from the genus Ceratopetalum. This genus was previously described to be limited in range to the Southern Hemisphere during the Cretaceous. 

Why Is The Discovery Surprising?

Yet, the new fossils were found on Sucia Island in Washington, which is in the Northern Hemisphere. Due to the surprising discovery, paleobotanists are reconsidering how extended their range may have truly been and how it may have occurred, according to the study. 

Keana Tang, the lead author of the study, said that in the paper, the researchers were looking at two fossils they had assigned to the genus Ceratopetalum, which is the flowering-plant family Cunoniaceae, according to a statement issued by KU. Tang, who is a doctoral student in ecology and evolutionary biology at KU and the KU Biodiversity Institute and Natural History Museum in Kansas, US, further said that both the family Cunoniaceae and the genus Ceratopetalum still have living members today. She said that what is interesting is that the genus Ceratopetalum is now only found in Australia. 

The entire family is restricted to the Southern Hemisphere, so it is weird to find this fossil all the way up here in the Northern Hemisphere, she explained. The researchers thought, "Whoa, how did this get here?"

Since the two new fossil species were found in Sucia Island, the researchers dubbed the new fossil species Ceratopetalum suciensis, according to the study. 

Where Are Modern Versions Of Genus  Ceratopetalum Found Today?

Modern versions of the genus Ceratopetalum are found in the wet tropical rainforests of Australia. In these rainforests, the modern versions of the genus Ceratopetalum play an important role in ecosystems, the study said.

Tang said that one will find forests that are just dominated by these species. 

The Plants Are Thought To Have Originated In Ancient Gondwana

According to the statement, the researcher said that the findings are made more significant because Ceratopetalum and the larger family Cunoniaceae are part of "Paleo-Antarctic Lineages", or PARLs. These are plants thought to have originated in the ancient Gondwana landmass before spreading northward. Gondwana was an ancient supercontinent that split up into a number of landmasses 180 million years ago. These land masses are, Africa, South America, Australia, Antarctica, the Indian subcontinent, and the Arabian Peninsula. 

Therefore, a better understanding of how Ceratopetalum extended its range could better inform scientists how an important larger group of plants widened its range through geologic time, according to the study. 

Quoting Tang, the statement said that PARLs have a joint history where they were likely around Antarctica and spread northward as time progressed and tectonic plates changed, causing the climate to change. She explained that as Antarctica is getting colder, these plants are moving up to South America, South Africa, and Australia. 

Tang further said that is interesting because the Paleo-Antarctic Lineages are all expected to have a southern origin. The discovery of the fruit species in the Northern Hemisphere brings up new questions, she said. 

Some of the questions include whether the family Cunoniaceae was cosmopolitan (found everywhere), or was this kind of a lucky exchange, Tang said. 

What Do The Findings Suggest?

The findings highlight new possibilities for a biotic exchange between North America and South America-Antarctica that may have occurred during the Late Cretaceous, according to Brian Atkinson, a co-author of the study.

He said that in some ways, this is like finding a penguin in North America.

The Fossils Were Collected By Two Fossil Hunters

Fossil hunters David Starr and Jim Goedert had collected the Ceratopetalum suciensis fossils on Sucia Island, according to the statement. Then, Selena Smith, another co-author of the study, performed a Micro-CT scan of the fossils at the University of Michigan. 

Analysing The Fossils Through The Cellulose Acetate Peeling Technique

Using a painstaking process called the cellulose acetate peeling technique, Tang analysed the fossils layer by layer. 

Tang said that she started peeling the rock, according to the statement. She explained how she performed a series of steps to polish the face of the fossil. 

The fossil was dipped into five per cent hydrochloric acid for a couple of seconds. After that, the rock was rinsed off with water, according to Tang. 

Then, the rock was rinsed with acetone, and the plastic sheet, which is the cellulose acetate sheet, was obtained. After that, the fossil face was sprayed with acetone again, and the sheet was layed down. As a result of the entire process, a very, very thin section of the rock, measuring a few micrometres, is obtained. Tang said that is nice because one can go through the entire fossil and pick up different structures hiding in the rock matrix which one might miss in a Micro-CT scan. 

The research suggests that the Pacific Northwest, where Ceratopetalum suciensis was discovered, is a promising region for further work by paleobotanists. Tang said there is just so much to look into, especially in the Western coast of North America, according to the statement. She further said that she thinks a lot of the world of paleobotany has been situated along the East Coast or the Western interior.