May 24, 2022 1:03 am

The oldest sponges in the world found in Ciudad Real, Spain

Francis Martin Leon 5 min
Mollusk remains. (a, c) Axial and oblique sections of Anabarella sp., a putative monoplacophore mollusc (Fon61, 35). (b) Vertical section of Anabarella sp. (Fon4), (d) Oblique section of an ornate Anabarella type (Fon35). See texts and figure in the final reference. Cambridge University Press.

An international and multidisciplinary investigation that has the participation of the Complutense University of Madrid (UCM) concludes with the discovery of the mineralized fossil remains of the oldest sponges in the world -530 million years- in the phosphate deposits of Fontanarejo (Ciudad Real).

These deposits were first described about 50 years ago, but had not been studied in detail until now. Spicules were discovered among the fossil remains -silicon units that make up the skeleton- of two types of sponges: hexactinillida Y demosponges.

It should be noted that some of the spicules are structured, that is, connected with others, retaining practically the same position as the original organism.”, highlights Pablo Suárez, researcher at the UCM Department of Geodynamics, Stratigraphy and Paleontology, and one of the authors of the study published in Geological Magazine.

Fontanarejo, Ciudad Real, on the Iberian Peninsula. Wikipedia

Sponges can have two types of skeleton: mineralized (as in the case of sponges in Castilla-La Mancha), composed of structured spicules, or non-mineralized (formed by organic molecules that degrade).

The sponge spicules in these phosphates are the oldest found to date, along with other specimens in China, with the difference that the latter are not structured, so the spicules in Fontanarejo would be the oldest in such good condition. conservation”, clarifies Suarez.

A publication from a few months ago shows fossils dating back about 890 million years, which were proposed as the remains of unmineralized sponges. The Fontanarejo spicules would thus be direct and unequivocal remains of the oldest sponges in the world.

Sponges are considered to be the first animals to evolve, so this discovery offers new information on the evolution of living beings.

Apart from the UCM, the University of Göttingen, the University of Tubingen (both in Germany) and the Nanjing Institute of Geology (China) also participated in the research.

To carry out the study, the researchers carried out fieldwork in Fontanarejo in 2019, where they carried out geological mapping and took more than 200 samples. Of these, 120 thin slices (small pieces of rock about 30 microns thick) were cut and studied using different techniques, both microscopic and chemical analysis.

Another of the main conclusions of the work is the dating of the deposits. It was already known that, compared to other equivalents in nearby areas, the Fontanarejo deposits belonged to the early Cambrian period (between 500 and 540 million years ago).

The discovery of the remains of Anabarella, a type of mollusk, helped pin the age down to about 530 million years, at the end of an age within the Cambrian period known to geologists as the Fortunian.”, indicates Suarez.

Microbes in phosphates

Phosphates are minerals used mainly in the agri-food industry, since phosphate can be extracted from them, which is a key element in many fertilizers.

The Fontanarejo phosphates on which the sponges have fossilized preserve a large amount of evidence of an origin associated with microbial communities, including the preservation of stranded forms of some of the original microbial deposits.

Phosphate deposits form very quickly after the death of sponges, which would probably live in association with microbial communities. This would explain the fact that sponge fossils are well preserved.”, concludes Suarez.

The Fontanarejo sponges lived on a sea shelf, along with those microbes and other organisms. The tides and storms transported all their remains to deeper waters, where they were buried under other layers of sediment, thus favoring their conservation. Millions of years later, the Variscan orogeny (which formed Pangea) raised these deposits, forming mountains, whose erosion has ended up showing all these fossils on the surface of the center of the Iberian Peninsula.


Revisiting the phosphorite deposit of Fontanarejo (central Spain): new window into the early Cambrian evolution of sponges and the microbial origin of phosphorites. Joachim Reitner, Cui Luo, Pablo Suarez-Gonzalez and Jan-Peter Duda
Cambridge University Press, Geological Magazine

This entry was posted in Reports on 05 Feb 2022 by Francisco Martín León

Comments (0)

Leave a Reply

Your email address will not be published.