Scleritome Week: A Mystery Ending

Welcome to the last post for Scleritome Week. I hope you've enjoyed reading it as much as I've enjoyed writing and researching it, and that it's brought a few surprises (it has for me - I actually expected chancelloriids to be a lot more like sponges, and if you look closely you might notice that I actually referred to them as such in the machaeridian post). This week I've brought you mystery fish, armoured worms, and an animal that one researcher reconstructed looking like one of the Ophanim*. Most of the animals I've covered have become well-known throught the fortunate discoveries of articulated specimens, but I thought I'd end with a little reminder of just what made the scleritome animals so fascinating - the fact that for so many of them we don't yet know what the animal looked like.

*Third choir, comes after the Seraphim and Cherubim.



Eurytholia was described in 2001 (Sutton et al., 2001) for small sclerites the authors described as "hat-like" found from scattered locations in Europe and North America. Eurytholia sclerites are more or less oblong in shape, with a central ridge running parallel with the shorter sides. The figure above from Sutton et al. (2001) shows an assortment of specimens from different angles.

As yet, no articulated specimens showing what the rest of the animal looked like have been found, but the authors were able to make some inferences about it. The sclerites were exterior rather than interior - their microstructure indicates that they were secreted from the underside only, and some specimens show evidence of having been damaged while the animal was alive. They were unlikely to have functioned as teeth due to their unsuitable morphology. They also don't appear properly shaped to have overlapped each other. Due to the relative abundances of sclerites of different sizes, Sutton et al. suggest an "armoured slug" appearance rather like that known for Wiwaxia (reconstruction also from Sutton et al., 2001):



Personally, I can't help thinking it looks like a headless, limbless, tail-less ankylosaurian. But the wonderful thing is that we just don't know if Sutton et al. got it right. Their reconstruction seems plausible enough, but until we find an articulated specimen, who knows what kind of tentacled monstrosity Eurytholia might actually turn out to have been?

REFERENCES

Sutton, M. D., L. E. Holmer & L. Cherns. 2001. Small problematic phosphatic sclerites from the Ordovician of Iapetus. Journal of Paleontology 75 (1): 1-8.