The Oldest Mineralised Bryozoan?

By | April 21st, 2022|Adobe CS5, Dinosaur and Prehistoric Animal News Stories, Main Page, Palaeontological articles, Photos/Pictures of Fossils|0 Comments

Scientists from John Hopkins University (Baltimore, Maryland), Smith College (Northampton, Massachusetts) along with bryozoan expert Paul Taylor of the London Natural History Museum and another collaborator have published a paper in “Science Advances” reporting a possible earliest occurrence of palaeostomate bryozoans.

Cut slabs of bryomorph fossils from the Harkless Formation
Cut slabs of bryomorph fossils from the Harkless Formation (Gold Point, Nevada). Cross-sectional view showing round individual tubes (A). Longitudinal cut through organism showing growth form (B). Note scale equals 1,000 microns. Picture credit: Pruss et al.

Fossils from the Harkless Formation (Nevada)

Recently, Everything Dinosaur published a blog post about a scientific paper that came out late last year (October 2021), the study reported upon the identification a soft-bodied bryozoan Protomelission gatehousei from Early Cambrian strata: Early Cambrian Origin for the Bryozoa. The oldest previously accepted skeletal bryozoans occur in Lower Ordovician deposits, however, these researchers suggest that fossils found in strata from the Harkless Formation (Nevada, USA) are also bryozoans. The fossils show a radiating form preserved in limestone deposited during the Cambrian. If these fossils also represent bryozoans, they have a hard, mineralised skeleton.

Thin section images of a single bryomorph organism from the Harkless Formation (Nevada).
Thin section images of a single bryomorph organism from the Harkless Formation (Nevada). General fossil view (A). Sketches of the branching of daughter tubes from parent tubes (B). Note the formation of distinct skeletal walls from the parent during budding. Note scale bar equals 1 mm. Picture credit: Pruss et al.

All Skeletal Marine Invertebrate Phyla Appeared During the Cambrian Explosion

Previously, it had been thought that all skeletal marine invertebrate phyla appeared during the Cambrian explosion, except for Bryozoa with mineralised skeletons which were known from fossils dating from the Early Ordovician. If the small fossils identified in thin cross sections of Harkless Formation limestone are examples of bryozoans with a hard skeleton, then this evidence, in addition to the recent paper on the soft-bodied Cambrian bryozoan Protomelission (P. gatehousei), suggests an Early Cambrian origin for the Bryozoa and provides evidence to support the hypothesis that all types of skeletal marine invertebrate phyla evolved during the Cambrian.

If the Nevada fossils are confirmed as bryozoans, the appearance of a mineralised skeleton in this phylum would be pushed back by some 30 million years.

The scientific paper: “The oldest mineralized bryozoan? A possible palaeostomate in the lower Cambrian of Nevada, USA” by Sara B. Pruss, Lexie Leeser, Emily F. Smith, Andrey Yu. Zhuravlev and Paul D. Taylor published in Science Advances.