According to a team of paleontologists at the University of Edinburgh, UK, the first complex animals lived millions of years earlier than previously thought.
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.
The team, led by Prof. Rachel Wood of the University of Edinburgh’s School of GeoSciences, studied well-preserved fossils of Namacalathus hermanastes – an extinct species of marine animal that lived during the Ediacaran period, approximately 550 million years ago – from limestones of the Nama Group, Namibia.
The fossils reveal that Namacalathus hermanastes possessed a rigid skeleton made of calcium carbonate.
“Namacalathus hermanastes had an accretionary growth skeletal wall composed of a calcareous foliated ultrastructure together with columnar microlamellar inflections,” Prof. Wood and co-authors said.
“N. hermanastes additionally displays an internal organic-rich wall layer similar to that found in brachiopods and an internal budding being expressed in a symmetrical, bilateral pattern.”
Until now, the oldest evidence of complex animals – which succeeded more primitive creatures that often resembled sponges or coral – came from the Cambrian Period, which began around 541 million years ago.
Paleontologists had long suspected that complex animals had existed before then but, until now, they had no proof.
“This fossil has been known for a long time, and was assumed to have been a primitive animal, such as a sponge or coral,” Prof. Wood said.
“This study suggests that it was, in fact, more advanced,” he added.
“We have suspected that these complex animals were present in the Ediacaran, but this study provides the first proof.”
Genetic family tree data suggested that complex animals – known as bilaterians – evolved prior to the Cambrian period. The new findings suggest that they may have lived as early as 550 million years ago, during the late Ediacaran period.
The results were published online November 4 in the journal Proceedings of the Royal Society B.
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A.Yu. Zhuravlev et al. Ediacaran skeletal metazoan interpreted as a lophophorate. Proceedings of the Royal Society B, published online November 04, 2015; doi: 10.1098/rspb.2015.1860
