Photo: UHH/Ernst

Living bryozoan Electra pilosa, Baltic Sea.

Many animal groups trace their origins to the so-called “Cambrian”—the geological period about 500 million years ago when the diversity of life in the oceans began to expand rapidly. At that time, numerous innovations in the animal kingdom emerged relatively suddenly, such as hard body parts that have survived as fossils. These shells and skeletons now provide researchers with insights into the evolution of life on Earth.

A team from China, Sweden, Australia, and Germany has now been able to study exceptionally well-preserved fossils of so-called bryozoans. These invertebrates still exist today, although not exactly in their original form. A defining characteristic is their colonial lifestyle: many individual microscopic organisms form a shared, complex structure, often composed of calcium carbonate.

The fossils studied come from the Xiannüdong Formation, a rock layer formed during the Cambrian period in China’s Shaanxi Province. Within this formation, the research team discovered new specimens of the previously known bryozoan species Protomelission gatehousei and identified a previously unknown species, Dayingomelission hexaclitia. Both organisms lived around 520 million years ago. Until now, there had been no evidence of these animals from that period.

“The results of our work show that bryozoans appeared earlier and were more widespread in the Cambrian period than previously thought,” says Dr. Andrej Ernst, a co-author of the study from the Department of Earth System Sciences at the University of Hamburg. In addition, the research provides new insights into a key evolutionary innovation: the coexistence of individuals in complex colonies with a distinct division of labor among members.

In addition to skeletal structures, the fossils even contained parts of the internal soft tissue, as this had been mineralized by phosphate. Modern imaging techniques made it possible to identify fine anatomical details, including membrane-like structures, characteristic spines, and individual muscle fibers. At the same time, the fossils reveal the modular skeletons typical of bryozoans.

“The results of our work show that bryozoans underwent a significant evolution during the Cambrian period that had remained undiscovered until recently,” says Dr. Ernst. “Further discoveries from this period will shed even more light on the evolution of life on Earth in the future.”

 Link zur Originalpublikation (englisch). 

(This content was translated automatically)