Researchers have uncovered a 550-million-year-old sea sponge fossil that provides a missing link in the evolutionary history of Earth's earliest animals, according to ScienceDaily.
The discovery, led by Virginia Tech geobiologist Shuhai Xiao, helps explain a 160-million-year discrepancy between molecular clock data and the physical fossil record.
While genetic evidence suggests sponges evolved around 700 million years ago, convincing fossils only appear around 540 million years ago. The new specimen, found along the Yangtze River in China, falls directly within this period of missing history.
According to the report from ScienceDaily, the team proposes that the earliest sponges lacked the mineralized skeletons that make modern species easy to find.
“If you extrapolate back, then perhaps the researchers found the first ones were soft-bodied creatures with entirely organic skeletons and no minerals at all,” Xiao said, as reported by the outlet.
He noted that such organisms would rarely survive fossilization except under extremely specific, rapid-burial conditions.
A complex find
The fossil features a detailed surface pattern of regular, box-like shapes. Researchers believe this pattern indicates a close relationship to certain species of glass sponges.
Size was another unexpected factor in the find. Alex Liu, a collaborator from the University of Cambridge, noted that the fossil measures approximately 15 inches long.
“When searching for fossils of early sponges I had expected them to be very small,” Liu said, according to the source.
Xiao first encountered the specimen five years ago via a photograph sent by a collaborator. He recognized its significance immediately.
“I had never seen anything like it before,” Xiao said. “Almost immediately, I realized that it was something new.”
The study, published in the journal Nature, suggests that scientists must rethink how they hunt for the origins of animal life, as the earliest ancestors may have been too soft to leave a trace.
