Evolutionary Link

Paleontologists have described the first three-dimensional preservation of soft tissue in Namacalathus hermanastes, a skeletal metazoan (multicellular animal) that lived some 547 million years ago (Ediacaran period) in what is now Namibia, and established a strong evolutionary link between Ediacaran and early Cambrian metazoans.

Namacalathus (individuals numbered). Centimeter scale. Image credit: Shore et al., doi: 10.1126/sciadv.abf2933.

Until recently, little was known about the origins of animals that evolved during the Cambrian explosion event because of a lack of well-preserved fossil evidence.

The mysterious origins of animals that evolved at this time baffled 19th century naturalist Charles Darwin. It is often referred to as Darwin’s dilemma.

Prior to the new study, it had proven difficult to trace links with earlier animals because their soft tissues — which provide vital clues about the animals’ ancestry — almost always break down over time.

During fieldwork in Namibia, University of Edinburgh’s Professor Rachel Wood and colleagues unearthed the well-preserved fossilized remains of Namacalathus hermanastes.

Using an X-ray imaging technique, they found some of the animals’ soft tissues immaculately preserved inside the fossils by a metallic mineral called pyrite.

Until now, paleontologists had only ever identified skeletal remains of Namacalathus hermanastes.

Reconstruction of the living Namacalathus: 1 – stem; 2 – parental cup; 3 – daughter cups; 4 – hollow ciliated tentacles; 5 – spines; 6 – lateral lumen; 7 – central opening; 8 – inner skeletal layer, foliated with columnar microlamellar inflections; 9 – internal (middle) skeletal later, organic rich; 10 – external outer skeletal layer, foliated with columnar skeletal inflections. Image credit: J. Sibbick.

Professor Wood and co-authors then examined the soft tissues of the Ediacaran animal and compared them with those in animals that evolved later.

They found that Namacalathus hermanastes was an early ancestor of species that appeared during the Cambrian explosion. Among them are types of prehistoric worms and mollusks.

“These are exceptional fossils, which give us a glimpse into the biological affinity of some of the oldest animals,” Professor Wood said.

“They help us trace the roots of the Cambrian explosion and the origin of modern animal groups.”

“Such preservation opens up many new avenues of research into the history of life which was previously not possible.”

The study was published in the journal Science Advances.

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A.J. Shore et al. 2021. Ediacaran metazoan reveals lophotrochozoan affinity and deepens root of Cambrian Explosion. Science Advances 7 (1): eabf2933; doi: 10.1126/sciadv.abf2933