Conodonta: Overview (3)

Cambrian Cousins from Kunming

But what's this? Could it be some previously unpublished early conodont with extraordinary preservation which we have likewise defaced with our idiosyncratic (or simply idiotic) concept of the conodont cranium?  Actually, no. What you behold is the cranium of the Cambrian Haikouichthys, as interpreted by an all-star cast, including Degan Shu, Simon Conway Morris, and Phillipe Janvier. Shu et al. (2003). To our eyes (which may lack the acuity of a Crawling Eye conodont) it differs only in detail from a conodont. It has only anterior "plates" instead of the hypertrophied pulley system of the later conodonts. The conodont element on the left side is obvious if you are looking for it. It curves around the outside of the "plate," and is present only as a curved section of ?bone with a small, anteromedially directed tooth. The right-hand element is broken, but the curved region and tooth are still evident. The elements may also continue posteriorly, although that may well be an artifact of taphonomy or preparation. The eyes are where they belong, as are the other structures. The otic capsule looks exactly like the same structure in the conodont we labelled on the previous page. The arcualia (better illustrated by other images in the paper) are quite similar. We are forced to concede only the presence of a branchial apparatus. In fact, there is little, and perhaps nothing at all, which distinguishes Haikouichthys from a conodont.

We have now gone so far out on a limb of the tree of life, that our position could scarcely be more insecure. But, at the same time, nothing is likely to make us look any more foolish than we already do.  Given these parameters, we unhesitatingly add the obvious from Shu et al. (1999): the structure we call a conodont element in Haikouichthys also appears to be homologous to the branchial bars, as shown in the image of the holotype of Haikouichthys.

If this goes on, we will be forced to take ourselves seriously or abandon the enterprise completely.

ATW051015 

Peering or Pouting?

Ultimately, our Paleozoic friend looks a bit more like the figure on the left. Much less cute than the Crawling Eye, but more functional. We have shown the S-elements as if they protruded from the mouth, which is quite unnecessary. The conodont may have, instead, been capable of an enormous pout, with elastic tissue connecting the rami of the S-elements like a gigantic lower lip. This would create a scooping action which might, or might not, have been useful, depending on diet and substrate. However that may be, it clearly makes more sense for the organism to have a big mouth in front, than to peer endlessly off to the side. ATW020727.

Web Annotations

In spite of our expectations in 2002, conodont phylogeny remains undeveloped. The most recent tree we know of is reflected in the cladograms at Mikko's Phylogeny Conodonta.  Hidden World of the Conodonta has a good introduction to conodont paleontology -- particularly its practical side.

There are a number of nice on-line collections, including Conodont Collection, James Davison and a small collection of really big images at Geological collections- IMAGES OF FOSSILS AND ROCKS.