KUNMING -- Chinese scientists have discovered well-preserved multicellular animal fossils in Ediacaran strata of eastern Yunnan, indicating that complex animal communities existed in oceans long before the Cambrian explosion.

The study, carried out by researchers from Yunnan University and the University of Oxford, was recently published online in the journal Science.

Using advanced imaging techniques, the team identified diverse early life forms from numerous soft-bodied fossils, and most importantly, they found large numbers of simple worm-like creatures that are among the first animals with symmetrical bodies.

These creatures had basic body parts like a head and a gut and could move freely. The discovery fills a major gap in the fossil record of how these early animals evolved.

The researchers also found abundant advanced early animal fossils belonging to deuterostomes -- the broad group that later gave rise to chordates, the major group that includes vertebrates (animals with backbones).

These fossils look very similar to those found in famous Cambrian sites, suggesting these key animal groups already existed in the Precambrian Ediacaran. The discovery further implies that chordates -- the lineage that includes humans and all other vertebrates -- may have also appeared by this time, offering new clues about their early evolution.

The findings are believed to be significant for resolving one of evolutionary biology's longstanding puzzles, known as "Darwin's Dilemma."

In On the Origin of Species, Charles Darwin viewed the lack of Precambrian animal fossils as a major challenge to his theory of gradual evolution, as complex animals appear abruptly in early Cambrian strata with no clear ancestral forms. In particular, actual body fossils of bilaterian animals (animals with symmetrical left and right sides), which make up roughly 98 percent of all animal species, are extremely rare from geological periods before the Cambrian.

For more than a century, searching for early bilaterian fossils has been a key scientific goal to address this paradox.

According to Cong Peiyun, a researcher at the Institute of Palaeontology, Yunnan University, the new fossils found in eastern Yunnan confirm Darwin's century-old conjecture that the sudden appearance of animals in the Cambrian is an illusion caused by an incomplete fossil record.

Cong noted that eastern Yunnan is a global hotspot for geological and fossil research across the Ediacaran-Cambrian transition, with unusually complete records and exquisitely preserved fossils that show how life evolved.

Chinese scientists have conducted fieldwork in the region since 2017, unearthing multiple new fossil-bearing sections and large numbers of specimens.

"Kunming and Yuxi in Yunnan province, in particular, are key regions for studying the origin and early evolution of animals, with extraordinary scientific significance," he added.