Fossils over 500 million years old reveal the oldest hard-skeletoned bryozoans

(ORDO NEWS) — Paleontologists have examined fossils from 514 to 509 million years old found in the United States and concluded that they may be mineralized bryozoan skeletons.

In an article published in the journal Science Advances, the scientists note that in this case, this finding pushes back the appearance of a solid skeleton in bryozoans by 30 million years.

Fossils over 500 million years old reveal the oldest hard skeletoned bryozoans 2
Fossils over 500 million years old reveal the oldest hard-shelled bryozoans

At the beginning of the Cambrian – about 540 million years ago – representatives of the main types of animals appear sharply in the fossil record, many of which had mineralized structures.

However, among the participants in this explosive radiation, which was called the Cambrian explosion, there were no bryozoans (Bryozoa) – colonial filter-feeders resembling corals – although the mineralized exoskeleton is also characteristic of this group.

Fossils over 500 million years old reveal the oldest hard skeletoned bryozoans 3
Variety of modern bryozoans

The generally recognized oldest hard skeletons of bryozoans were until recently found in deposits of the Tremadocian stage of the Ordovician (485.4–477.7 million years ago), but paleontologists suspected that bryozoans must have appeared much earlier.

In 2021, scientists introduced the world to Protomelission gatehousei, a bryozoan whose fossils have been found in Cambrian deposits of southern China dating from 521 to 514 million years old and in slightly younger deposits in Australia. However, the skeleton of this bryozoan was not mineralized.

American paleontologists led by Sara B. Pruss of Smith College studied the fossils of the Cambrian Harkless Formation in the western United States, which ranges in age from 514 to 509 million years (stage 4).

The attention of researchers was attracted by fossils in the form of thin branching tubes filled with rock, up to three millimeters long.

The scientists made petrographic sections of sediments with fossils and examined them under a microscope. The researchers concluded that these fossils are very similar to hard-skeletoned bryozoan fossils from Ordovician deposits. In addition, scientists noted similarities with P. gatehousei.

Pruss and her colleagues did not describe the taxonomic identity of the fossils and limited themselves to the assumption that these were mineralized bryozoan skeletons.

The authors note that further studies of the Harkless Formation will make it possible to more accurately determine the identity of these fossils, especially if fossil remains of ancestrula, the first zooid that gives rise to a colony, are found.

If these are indeed bryozoans, then this finding would delay the appearance of a mineralized skeleton in this group by about 30 million years.

The Cambrian origin of bryozoans was also confirmed by the recent work of biologists from 17 countries, who compiled the most complete phylogenetic tree of this group.

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