Ordovician Receptaculite specimen: Sponge or Algae?

[ntloux]

I am attaching two images of an Odovician receptaculite fossil from Scott City, VA.  As it was considered to be a sponge when I acquired it I was thrilled because I had only previously seen disarticulated sponge spicules.  There appears to be a more recent debate suggesting that receptaculites are algae.  If one accepts the first image as the top of the fossil then the structure is consistent with sponge diagrams I saw in a high school Biology class.  So how about some opinions on whether or not it is a sponge or fossil algae.

 

 

So,is this the top?

 

 

Or is this the top?

 

[piranha]

The genus Receptaculites is restricted to the Devonian.  All the receptaculitids from the Ordovician are now classified as one genus: Fisherites

 

"The best-known receptaculitids are the Ordovician to Carboniferous family Receptaculitidae, which in the Ordovician consists of a single genus, Fisherites, with nine species ranging from TS.2c through 6b.  They are the largest receptaculitids known and are widely distributed in limestones and dolomites.  Their wide geographic distribution is comparable to that of soanitids, except that the concentration of their distribution is in central North America.  They are also found in the Canadian Arctic, Greenland, Baltoscandia, Burma, North Korea, Thailand, and the Argentine Precordillera but have not been reported from China."

 

Nitecki, M.H., Webby, B.D., Spjeldnaes, N., Yong-Yi, Z. 2004

Receptaculitids and Algae. 

In: The Great Ordovician Biodiversification Event.

Columbia University Press, 484 pp.

 

 

The classification of receptaculitids is not algae or sponge, it is still unresolved Problematica.

 

"We know that we have succeeded only in showing that receptaculitids were neither sponges, archaeocyathids, nor dasyclads, because the cumulative receptaculitid characters are not those of sponges or of algae. It is surely premature to ask what they were we must still wait to know that. We are far from providing final answers, but we hope that others will be stimulated to ask new questions, and to accept receptaculitids as more than the sum of their characters. The preponderant lesson from our morphological analyses has shown us that complete understanding of the nature of the receptaculitids is not yet possible; therefore, in order to build a strong case on the nature of receptaculitids we either had to endlessly speculate, or admit our ignorance. The German idioms and expressions have changed since Rauff wrote (1892a:648), and the current rendition of his conclusions as shown in our Dedication (p. v) may now be rephrased. We now believe that we do not know enough to be definitive, and have been left no choice but to follow Rauff in retaining receptaculitids in the Problematica."

 

(Translation of Rauff 1892a:648)

"My investigation on the true nature of receptaculitids has had the painful result of again evicting these interesting fossils from their taxonomic position, and setting them adrift once more. Perhaps my observations on their most extraordinary structures will help some luckier, more informed person discover their true affinities. It is this hope which has caused me to publish this work even without its most important conclusion; at least it may serve as a basis for further analysis. Receptaculitids are again removed from their taxonomic position, without resolving their systematics, and it is hoped that the present paper will form the bases for future phylogenetic analyses." 

 

Nitecki, M.H., Mutvei, H. Nitecki, D.V. 1999

Receptaculitids: A Phylogenetic Debate on a Problematic Fossil Taxon.

Springer Scientific Publishing, 241 pp.

[Kato]

That spiral in the 'top' is amazing as are the shapes of the plates

[JBkansas]

These are one of the coolest "common" fossils that I'd never heard of before joining the group.

[Kato]

22 minutes ago, JBkansas said:

These are one of the coolest "common" fossils that I'd never heard of before joining the group.

 

I wish they were common here in southern New Mexico where we have Ordovician formations approaching 300 ft thick overall from oldest to youngest. Now that I've seen this example it gives me something specific to look for.

[JBkansas]

6 minutes ago, Kato said:

 

I wish they were common here in southern New Mexico where we have Ordovician formations approaching 300 ft thick overall from oldest to youngest. Now that I've seen this example it gives me something specific to look for.

Our rocks are all Permian/Carboniferous but auction sites have them by the boxful so they must be very common somewhere.

[ntloux]

I wish to sincerely thank Pirahna for the in depth information on the subject.

[doushantuo]

shape variability:

Edited March 12 by doushantuo
from Guembel's extensive study of Receptaculitids