Conical Problematica

Scattered throughout the fossil record are little mysteries, organisms whose remains have been preserved but which are not obviously relatable to any more familiar group. Either their remains are too simple to preserve much evidence of their affinities (as with the 'tubular problematica' I've discussed before), or they are too distinct from other organisms for their affinities to be clear, or both, or some other reason. Unless they are particularly common or otherwise significant, most of these problematica are probably doomed to remain so. Case in point:



The figures above show Asymmetroconus splendidus, described by Korde in 1975 from the Albian (early Cretaceous) of the Crimea. The photos are of thin sections of the fossils; the complete skeleton would have probably been shaped rather like a wine goblet. The largest specimens of Asymmetroconus were just under 8 mm in height. In the same paper, Korde described a number of similar fossils aged from the Albian to the Danian (earliest Palaeocene), assigning them all to the new order Asymmetroconida. Korde attributed the asymmetroconidans to the Hydroconozoa, a group of similar fossils he had himself described previously from the early Cambrian. Hydroconozoa have generally been assigned to the Cnidaria, though their exact position therein remains obscure. Asymmetroconida resembled hydroconozoans in being small and goblet-shaped, with a conical interior to the cup and a basal globular hollow below the point of the cone. However, they differed from Cambrian hydroconozoans in their skeletal microstructure and in the asymmetry of the cup, with one side much thicker than the other. Rozanov & Zhuravlev (1992) later dismissed the idea of Mesozoic hydroconozoans, stating simply that structures described as such had 'little in common with this group'. No alternative identification of the Asymmetroconida has ever been proposed, and they do not appear to have been properly studied since Korde's original description.


Reconstruction of the hydroconozoan Hydroconus mirabilis, from Rozanov & Zhuravlev (1992). Whether actually related or not, the Asymmetroconida would have probably looked superficially similar.

REFERENCES

Korde, K. B. 1975. [Hydroconozoa from Cretaceous and Palaeocene deposits of the Crimea]. In: Shimansky, V. N., & A. N. Soloviev (eds) Razvitie i smena organičeskogo mira na rubeže Mezozoâ i Kajnozoâ. Novye dankye o razvitii fauny pp. 32-38. Nauka: Moscow. [in Russian]

Rozanov, A. Yu., & A. Yu. Zhuravlev. 1992. The lower Cambrian fossil record of the Soviet Union. In: Lipps, J. H., & P. W. Signor (eds) Origin and Early Evolution of the Metazoa pp. 205-282. Plenum Press: New York.