Paleontologists have described the first three-dimensional preservation of soft tissue in Namacalathus hermanastes, a skeletal metazoan (multicellular animal) that lived about 547 million years ago (Ediacaran period) in present-day Namibia, and established a strong evolutionary link between Ediacaran and early Cambrian metasoans.
Namacalathus (individual numbers). Centimeter scale. Image Credit: Shore et al., doi: 10.1126 / sciadv.abf2933.
Until recently, little was known about the origin of animals that evolved during the Cambrian explosion event due to a lack of preserved fossil evidence.
The mysterious origins of animals that evolved during this time amazed 19th-century naturalist Charles Darwin. This is often called Darwin’s dilemma.
Prior to the new study, it was difficult to detect ties with earlier animals because their soft tissues – which provide important clues about the descent of the animals – almost always break down over time.
During fieldwork in Namibia, Professor Rachel Wood of the University of Edinburgh and colleagues discovered the well-preserved fossils of Namacalathus hermanastes.
Using an X-ray imaging technique, they found that some of the soft tissues of the animals were immaculately preserved within the fossils by a metal mineral called pyrite.
Until now, paleontologists have only skeletal remains of Namacalathus hermanastes.
Reconstruction of the living Namacalathus: 1 – strain; 2 – parent cup; 3 – daughter cups; 4 – hollow silica tentacles; 5 – spines; 6 – lateral lumen; 7 – central opening; 8 – inner skeletal layer, stained with columnar microlamellar bends; 9 – inner (middle) skeleton later, organically rich; 10 – outer outer skeletal layer, filled with columnar skeletal deflections. Image Credit: J. Sibbick.
Professor Wood and co-authors then examined the soft tissues of the Ediacaran animal and compared them to those of animals that developed later.
They found it Namacalathus hermanastes was an early ancestor of species that appeared during the Cambrian explosion. Among them are species of prehistoric worms and molluscs.
“These are extraordinary fossils that give us a glimpse into the biological relationship of some of the oldest animals,” Professor Wood said.
“They help us trace the roots of the Cambrian explosion and the origins of modern animal groups.”
“Such preservation offers many new possibilities for research into the life history that was not possible before.”
The study was published in the journal Scientific progress.
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AJ Shore et al. 2021. Ediacaran metazoan reveals lophotrochozoan affinity and deepens root of Cambrian explosion. Scientific progress 7 (1): eabf2933; doi: 10.1126 / sciadv.abf2933