The Conulariid Interior

Today we check in with one of the more unusual members of Paleozoic seafloor communities: Conulariida. The "four-sided herringboned ice cream cones" still hold many mysteries (including the mystery of the whereabouts of George Sinclair's collection; I'd still be interested in knowing more about that!). One of the major mysteries has been what exactly the soft parts of the animal looked like; if we knew that, we'd know a lot more about how conulariids are related to other animals, how they fed, how they looked, etc. It's generally assumed they are some kind of cnidarian (along with corals, jellyfish, sea anemones, and so on). Wikipedia has them potentially aligned with Staurozoa, which today is represented by stalked jellyfish (worth looking up if you've never heard of stalked jellyfish).

A cnidarian identity would imply stinging tentacles, but these have never been firmly identified. Soft parts in general are not particularly well-known for conulariids, which makes sense because preserving the soft parts of cnidarians is not something that just happens as a matter of course. (We could use a late Paleozoic amber-producing coastal forest that was flooded by a storm that dredged up all kinds of marine organisms.) There were some potential finds in the 1980s, as discussed in Babcock and Feldman (1986a) and Sendino et al. (2023) (see Figure 30 in Babcock and Feldman 1986b for internal casts and x-ray image of a conulariid's putative guts). Recently, Sendino et al. (2023) have applied X-ray micro-Computed Tomography (μCT) to a collection of well-preserved Pennsylvanian-age conulariids from the Wewoka Formation of Oklahoma and the Finis Shale Member of the Grand Formation of Texas.

What can μCT see in a conulariid? First off, it can see the concealed end of one conulariid partially within another conulariid. This is a good sign as a sanity check because we can confirm it can discern something that obviously should be there. With that encouraging information in mind, what else is there?

Figure 4 in Sendino et al. (2023); it's always good to see what you *ought* to see. CC BY 4.0.

Sendino et al. (2023) found "longitudinal bundles" in many of their specimens, i.e., oriented apex–aperture. The authors interpreted these as muscles for closing the flaps of the aperture. (This tells us a few things about the muscular and nervous systems of conulariids.) In some examples there was also an internal structure they interpreted as a possible gastric cavity. In other specimens, the internal sediment was clearly replaced, for example by sand, or contained other fossil material such as forams or a tiny drilled brachiopod. The internal sediment of some specimens appears to have been disrupted by later burrowing. A number of the conulariids also show scars from external attacks (conulariids seem to have been easy targets). The article, which is freely available, is heavily illustrated with μCT images, followed up by a series of supplementary files of large images.

And this is their basic interpretation (Figure 13). CC BY 4.0.

In other business: I'll be giving a talk for the Geological Society of Minnesota on Monday, May 8: "Snorkeling at Shadow Falls: Fossils of Minnesota". Non-members are welcome!

References

Babcock, L. E., and R. M. Feldmann. 1986a. Devonian and Mississippian conulariids of North America. part A. General description and Conularia. Annals of the Carnegie Museum 55:349–410.

Babcock, L. E., and R. M. Feldmann. 1986b. Devonian and Mississippian conulariids of North America. part B. Paraconularia, Reticulaconularia, new genus, and organisms rejected from Conulariida. Annals of the Carnegie Museum 55:411–479.

Sendino, C., B. Clark, A. C. Morandini, T. Salge, M. Lowe, and W. Rushlau. 2023. Internal conulariid structures unveiled using µCT. PalZ (2023). doi:https://doi.org/10.1007/s12542-023-00649-7.